Kit review – High Accuracy LC Meter

Hello readers

Time for another kit review. Lately one of my goals has been to make life easier and in doing so having some decent test equipment. One challenge of meeting that goal is (naturally) keeping the cost of things down to a reasonable level. Unfortunately my eyesight is not the best so I cannot read small capacitor markings – which makes a capacitance meter necessary. Although I have that function within my multimeter, it is often required to read resistors in the same work session.

Thus the reason for this kit review. A day trip to Altronics saw me return with (amongst other things) their High Precision LC Meter kit. The details were originally published in the May 2008 issue of Australia’s Silicon Chip magazine. The meter specifications are:

• Capacitance – 0.1pF to over 800 nF with four-digit resolution;
• Inductance – 10 nH to over 70 mH with four-digit resolution;
• Accuracy of better than +/- 1% of the reading;
• Automatic range selection, however only non-polarised capacitors can be measured.

The power drain is quite low,  between 8 (measurement) and 17 milliamps (calibration). Using a fresh 9V alkaline battery you should realise around fifty to sixty hours of continuous use. At this point some of you may be wondering if it is cheaper to purchase an LC meter or make your own. A quick search found the BK Precision 875B LCR meter with the same C range and a worse L range for over twice the price of the kit. Although we don’t have resistance measurement in our kit, if you are building this you already have a multimeter. So not bad value at all. And you can say you built it

Speaking of building, assembly time was just under two hours, and the kit itself is very well produced. The packaging was the typical retail bag:

The first thing that grabs your attention is the housing. It is a genuine, made in the US Hammond enclosure – and has all the required holes and LCD area punched out, so you don’t need to do any drilling at all:

The enclosure has nice non-slip rubberised edging (the grey area) and also allows for a 9V battery to be housed securely. The team at Altronics have done a great job in redesigning the kit for this enclosure, much more attractive than the magazine version. The PCB is solder-masked and silk-screened to fine standard:

There are two small boards to cut and file off from the main PCB. We will examine them later in the article. All required parts for completion were included, and it is good to see 1% resistors and an IC socket for the microcontroller:

At first I was a little disappointed to not have a backlit LCD module, however considering the meter is to be battery operated (however there is a DC socket for a plugpack) and you wouldn’t really be using this in the dark, a backlight wouldn’t be necessary. Construction was easy enough, the layout on the PCB is well labelled, and plenty of space between pins. Lately I have started using a lead-former, and can highly recommend the use of one:

Assembly was quite simple, just start with the lower profile components:

… then mount the LCD and the larger components:

… the switches and others – and we’re done:

The only problem at this point was the PCB holes for the selector switch, one hole was around 1mm from where it needed to be. Instead of drilling out the hole, it was easier to just bend up the legs of the switch and keep going:

At this stage one has to cut out two supports from the enclosure, which can be done easily. Then insert the PCB and solder to the sockets and power (9V battery snap). Initial testing was successful (after adjusting the LCD contrast…):

If you look at the area of PCB between the battery and the left-hand screw there are eight pins – these are four pairs of inputs used to help calibrate and check operation of the meter. For example, by placing a jumper over a pair you can display the oscillator frequency at various stages:

Furthermore, those links can also be used to fine-tune the meter. For example one can increase or decrease the scaling factor and the settings are then stored in the EEPROM within the microcontroller. However my example seemed ok from the start, so it was time to seal up the enclosure and get testing. Starting with a ceramic capacitor, the lowest value in stock:

Spot-on. That was a good start, however trying to bend the leads to match the binding posts was somewhat inconvenient, so I cut up some leads and fitted crocodile clips on the end. The meter’s zero button allows you to reset the measurement back to zero after attaching the leads, so stray capacitance can be taken into account.

Next, time to check the measurement with something more accurate, a 1% tolerance silvered-mica 100 picofarad capacitor:

Again, the meter came through right on specification. My apologies to those looking for inductor tests – I don’t have any in stock to try out. If you are really curious I could be persuaded to order some in, however as the capacitance measurement has been successful I am confident the inductance measurement would also fall within the meter’s specifications.

As shown earlier, there were two smaller PCBs included:

The top PCB is a shorting bar used to help zero the inductance reading, and the lower PCB is used to help measure smaller capacitors and also SMD units. A nice finishing touch that adds value to the meter. The only optional extra to consider would be a set of short leads with clips or probes to make measurement physically easier.

When reading this kit review it may appear to be somewhat positive and not critical at all. However it really is a  good instrument, considering the accuracy, price, and enjoyment from doing it yourself. It was interesting, easy to build, and will be very useful now and in the future. So if you are in the market for an LC meter, and don’t mind some work – you should add this kit to your checklist for consideration. It is available from Altronics stores and resellers.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Tutorial: Control AC outlets via SMS

Learn how to control AC outlets via SMS text message. This is chapter thirty-three of a series originally titled “Getting Started/Moving Forward with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Updated 02/03/2013

Assumed understanding for this article is found in part one. If you have not already done so, please read and understand it.

In this chapter we will continue with the use of the SM5100 cellular shield to turn digital outputs on and off via SMS. However please read chapters twenty-six and twenty-seven first if you are unfamiliar with using the GSM shield with Arduino. As an extension of chapter twenty-seven, we will use our Arduino to turn on or off AC outlets via a common remote-control AC outlet pack. Please note this is more of a commentary of my own experience, and not an exact tutorial. In other words, by reading this I hope you will gain some ideas into doing the necessary modifications yourself and in your own way.

Firstly, we need some remote-control AC outlets. Most electrical stores or giant retail warehouses may have something like this:

Nothing too original, just a wireless remote control that can switch on or off receiver outlets on a choice of four radio frequencies. Before moving forward I would like to acknowledge that this article was inspired by the wonderful book Practical Arduino – Cool Projects for Open Source Hardware by Jon Oxer and Hugh Blemings. In chapter two an appliance remote-control system is devised using a similar system.

At first glance the theory behind this project is quite simple – using the hardware in example 27.2, instead of controlling LEDs, activate the buttons on the wireless remote control for the AC outlets – leaving us with AC outlets controlled via SMS. However there are a few things to keep in mind and as discovered during the process, various pitfalls as well.

Before voiding the warranty on your remote control, it would be wise to test the range of the remote control to ensure it will actually work in your situation. I found this was made a lot easier by connecting a radio to the remote outlet – then you can hear when the outlet is on or off. If this is successful, make a note of the amount of time required to press the on and off buttons – as we need to control the delay in our Arduino sketch.

The next step is to crack open the remote control:

… and see what we have to work with:

Straight away there are two very annoying things – the first being the required power supply – 12 volts; and the second being the type of button contacts on the PCB. As you can see above we only have some minute PCB tracks to solder our wires to. It would be infinitely preferable to have a remote control that uses actual buttons soldered into a PCB, as you can easily desolder and replace them with wires to our Arduino system. However unless you can casually tear open the remote control packaging in the store before purchase, it can be difficult to determine the type of buttons in the remote.

As you can see in the photo above, there is an off and on pad/button each for four channels of receiver. In my example we will only use two of them to save time and space. The next question to solve is how to interface the Arduino digital outputs with the remote control. In Practical Arduino, the authors have used relays, but I don’t have any of those in stock. However I do have a quantity of common 4N25 optocouplers, so will use those instead. An optocoupler can be thought of as an electronic switch that is isolated from what is it controlling – see my article on optocouplers for more information.

Four optocouplers will be required, two for each radio channel. To mount them and the associated circuitry, we will use a blank protoshield and build the Arduino-remote control interface onto the shield. The circuitry for the optocoupler for each switch is very simple, we just need four of the following:

As the LED inside the optocoupler has a forward voltage of 1.2 volts at 10mA, the 390 ohm resistor is required as our Arduino digital out is 5 volts. Dout is connected to the particular digital out pin from the Arduino board. Pins 4 and 5 on the optocoupler are connected to each side of the button contact on our remote control.

The next consideration is the power supply. The remote control theoretically needs 12 volts, however the included battery only measured just over nine. However for the optimum range, the full 12 should be supplied. To save worrying about the battery, our example will provide 12V to the remote control. Furthermore, we also need to supply 5 volts at a higher current rating that can be supplied by our Arduino. In the previous GSM chapters, I have emphasised that the GSM shield can possibly draw up to two amps in current. So once again, please ensure your power supply can deliver the required amount of current. From experience in my location, I know that the GSM shield draws around 400~600 milliamps of current – which makes things smaller and less complex.

The project will be supplied 12 volts via a small TO-92 style 78L12 regulator, and 5 volts via a standard TO-220 style 7805 regulator. You could always use a 7812, the 78L12 was used as the current demand is lower and the casing is smaller. The power for the whole project will come from a 15V DC 1.5A power supply. So our project’s power supply schematic will be as follows:

Now to mount the optocouplers and the power circuitry on the blank protoshield. Like most things in life it helps to make a plan before moving forward. I like to use graph paper, each square representing a hole on the protoshield, to plan the component layout. For example:

It isn’t much, but it can really help. Don’t use mine – create your own, doing so is good practice. After checking the plan over, it is a simple task to get the shield together. Here is my prototype example:

It isn’t neat, but it works. The header pins are used to make connecting the wires a little easier, and the pins on the right hand side are used to import the 15V and export 12V for the remote.

While the soldering iron is hot, the wires need to be soldered to the remote control. Due to the unfortunate size of the PCB tracks, there wasn’t much space to work with:

But with time and patience, the wiring was attached:

Again, as this is a prototype the aesthetics of the modification are not that relevant. Be careful when handling the remote, as any force on the wiring can force the soldered wire up and break the PCB track. After soldering each pair of wires to the button pads, use the continuity function of a multimeter to check for shorts and adjust your work if necessary.

At this stage the AC remote control shield prototype is complete. It can be tested with a simple sketch to turn on and off the related digital outputs. For example, the following sketch will turn on and off each outlet in sequence:

Example 33.1

void setup()
{
  pinMode(9, OUTPUT); // 1 off
  pinMode(8, OUTPUT); // 1 on
  pinMode(5, OUTPUT); // 2 off
  pinMode(4, OUTPUT); // 2 on
}

void loop()
{
  // outlets on channel 1 on
  digitalWrite(8, HIGH);
  delay(1000);
  digitalWrite(8, LOW);
  delay(5000);
// outlets on channel 1 off
  digitalWrite(9, HIGH);
  delay(1000);
  digitalWrite(9, LOW);
  delay(5000);
  // outlets on channel 2 on
  digitalWrite(4, HIGH);
  delay(1000);
  digitalWrite(4, LOW);
  delay(5000);
// outlets on channel 2 off
  digitalWrite(5, HIGH);
  delay(1000);
  digitalWrite(5, LOW);
  delay(5000);
}

Now to get connected with our GSM shield. It is a simple task to insert the remote shield over the GSM shield combination, and to connect the appropriate power supply and (for example) GSM aerial. The control sketch is a slight modification of example 27.2, and is shown below:

Example 33.2

#include <SoftwareSerial.h> 
char inchar; 
SoftwareSerial cell(2,3);

int aon = 8;
int aoff = 9;
int bon = 4;
int boff = 5;
int pressdelay = 1000; // duration to activate a button on remote

void setup()
{
 // prepare the digital output pins
 pinMode(aon, OUTPUT);
 pinMode(aoff, OUTPUT);
 pinMode(bon, OUTPUT);
 pinMode(boff, OUTPUT);
 //Initialize GSM module serial port for communication.
 cell.begin(9600);
 delay(30000); // give time for GSM module to register on network etc.
 cell.println("AT+CMGF=1"); // set SMS mode to text
 delay(200);
 cell.println("AT+CNMI=3,3,0,0"); // set module to send SMS data to serial out upon receipt 
 delay(200);
}

void loop() 
{
 //If a character comes in from the cellular module...
 if(cell.available() >0)
 {
 inchar=cell.read(); 
 if (inchar=='#')
 {
 delay(10);
 inchar=cell.read(); 
 if (inchar=='a')
 {
 delay(10);
 inchar=cell.read();
 if (inchar=='0')
 {
 digitalWrite(aoff, HIGH);
 delay(pressdelay);
 digitalWrite(aoff, LOW);
 } 
 else if (inchar=='1')
 {
 digitalWrite(aon, HIGH);
 delay(pressdelay);
 digitalWrite(aon, LOW);

}
 delay(10);
 inchar=cell.read(); 
 if (inchar=='b')
 {
 inchar=cell.read();
 if (inchar=='0')
 {
 digitalWrite(boff, HIGH);
 delay(pressdelay);
 digitalWrite(boff, LOW);

} 
 else if (inchar=='1')
 {
 digitalWrite(bon, HIGH);
 delay(pressdelay);
 digitalWrite(bon, LOW);

}
 delay(10);
 inchar=cell.read(); 
 cell.println("AT+CMGD=1,4"); // delete all SMS
 }
 }
 }
 }
}

 

The variable pressdelay stores the amount of time in milliseconds to ‘press’ a remote control button. To control our outlets, we send a text message using the following syntax:

#axbx

Where a/b are remote channels one and two, and x is replaced with 0 for off and 1 for on.

So there you have it – controlling almost any AC powered device via text message from a cellular phone. Imagine trying to do that ten, or even five years ago. As always, now it is up to you and your imagination to find something to control or get up to other shenanigans.

Have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Kit review – Evil Mad Science Larson Scanner

Hello readers

Time yet again for another kit review. Today’s kit is the Larson Scanner from Evil Mad Science. What a different name for a company; their byline is “DIY and open source hardware for art, education and world domination”. Art? Yes. Education? Definitely. World domination? Possibly – you could use the blinking LEDs to hypnotise the less intelligent world leaders out there.

Anyhow, what is a Larson Scanner? Named in honour of Glen A. Larson the creator of television shows such as Battlestar Galactica and Knight Rider – as this kit recreates the left and right blinking motion used in props from those television shows. For example:

The kit itself is quite inexpensive, easy to assemble – yet can be as complex as you want it to be. More about that later, for now let’s put one together and see how it performs. There are two versions of the kit, one with 5mm clear LEDs and our review model with 10mm diffused red LEDs. The kit arrives inside a huge resealable anti-static bag, as such:

Upon opening the bag we have the following parts (there was an extra LED and resistor, thanks):

… the PCB:

… which is nicely done with a good silk-screen and solder mask. And finally:

A very handy item – a battery box with power switch. The kit is powered by 2 x AA cells (not included!). And finally, the instructions:

At this point you can see that this kit is designed for the beginner in mind. The instructions are easy to read, clear, and actually very well done. If you are looking for a kit to get someone interested in electronics and to practice their soldering, you could do a lot worse than use this kit.

Construction was very easy, starting with the resistors:

followed by the capacitor and button:

then the microcontroller:

… no IC socket. For a beginners’ kit, perhaps one should have been included. Next was the battery box. Some clever thinking has seen holes in the PCB to run the wires through before soldering into the board – doing so provides a good strain relief for them:

… and finally the LEDs. Beginners may solder them in one at a time:

however it is quicker to line them up all at once than solder in one batch:

… which leaves us with the final product:

Operation is very simple – the power switch is on the battery box. The button on the PCB controls the speed of LED scrolling, and if held down switches the brightness between low and high. Now for some action video of the Larson Scanner in operation:

Well that really was fun, a nice change from the usual things around here.

But wait, there’s more… although the Larson Scanner is a good training kit, it can also function in other interesting ways. The kit is completely open-source, you can download the PCB layout file, circuit schematic and microcontroller code. Get two or more and link them together to make a really wide LED display – expansion instructions are available from here. If you solder in a 6-pin PCB header to the area marked J1 on the PCB, you can reprogram the microcontroller using an STK500-compatible programmer.

After sitting my Larson Scanner next to the computer tower for a few minutes, I had contemplated fitting it into a 5.25″ drive bay to make my own Cylon PC, however that might be a little over the top. However my PC case has some dust filters on the front, which would allow LEDs to shine through in a nicely subdued way. Mounting the Larson Scanner PCB inside the computer case will be simple, and power can be sourced from the computer power supply – 5V is available from a disk drive power lead.

If you are going to modify your PC in a similar fashion, please read my disclaimer under “boring stuff” first.

The Larson Scanner can run on 3.3V without any alteration to the supplied components. What needs to be done is to use a voltage regulator to convert the 5V down to 3.3V. My example has used a 78L33 equivalent, the TI LP2950 as it is in stock. The power comes from a drive power cable splitter as such:

You may have a spare power plug in your machine, so can tap from that. 5V is the red lead, and GND is the adjacent black lead. Don’t use yellow – it is 12V. It is then a simple matter of running 5V from the red lead to pin 1 of the regulator, GND from the Larson Scanner and PC together to pin 2, and 3.3V out from the regulator to the PCB 3.3V. Insulation is important with this kind of work, so use plenty of heatshrink:

… then cover the whole lot up:

Now to locate a free power plug in the machine. It has been a while since opening the machine – time for a dust clean up as well:

Mounting the PCB is a temporary affair until I can find some insulated mounting  standoffs:

However it was worth the effort, the following video clip shows the results in action:

So there you have it. The Larson Scanner is an ideal kit for the beginner, lover of blinking LEDs, and anyone else that wants to have some easy blinking fun. You can buy Larson Scanner kits in Australia from Little Bird Electronics, or directly from Evil Mad Science for those elsewhere.

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts, follow me on twitter or facebook, or join our Google Group for further discussion.

High resolution images are available on flickr.

[Note - The kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Otherwise, have fun, be good to each other – and make something!

Kit review – Freeduino v1.22 Arduino-compatible

Hello readers

Time again for another kit review. Today we will examine the Freeduino Arduino Duemilanove-compatible board in a kit. It is always interesting to see how the different types and makes of Arduino-compatible boards present themselves, so this is review is an extension of that curiosity. This kit was originally designed by NKC Electronics and released under a Creative Commons license.

The packaging can either be classed as underwhelming or environmentally-friendly, as the kit arrives in several plastic resealable bags. Upon emptying them out we are presented with the following, the parts:

and the PCB:

Hopefully you noticed what ends up being the key features of this kit – the pre-soldered FTDI IC and mini-USB socket. This means the Freeduino can be used with a USB cable (not included) and not an expensive FTDI cable. The PCB itself is very solid, has a very descriptive silk-screen layer with all the component positions labelled, is solder-masked, and has nice rounded corners.

Reviewing the included parts did make me wonder why the supplier has used 5% carbon-film resistors and ceramic capacitors instead of polyesters (except for one). It turns out that Seeedstudio (the distributor for my example kit) claim 5% resistors are easier to read. Originally I claimed that this was an excuse to save a few cents, however a few people have said that such resistors are easier to read.

Furthermore, this one missed out on the polyfuse for USB overcurrent and short-circuit protection. And whether or not the larger tolerances affect the operation of the board, the cheaper components make the finished product look very 1977. However on a brighter note, an IC socket is included.

Assembly was quick and simple. There are excellent online instructions published by the Freeduino creator NKC available here. However you can also follow the silk-screen labels on the PCB as well. A good method is to start with the lowest-profile compontents, such as resistors and capacitors:

… then followed by the capacitors, crystal, LEDs and reset button:

Notice how the ceramic capacitors lead-spacing is too narrow for the holes on the PCB – this makes me think that the distributor has skimped out on the final product and been too lazy to update the PCB layout. The ATmega168 label is an example of this. Moving forward, the voltage regulator and sockets. The easiest way to solder in the shield sockets is to place them into the pins of an Arduino shield and solder – as such:

And there you have it, one Freediono v1.22 Arduino Duemilanove-compatible board:

The image above also displays another bugbear with this kit – the LED placement. When you have a shield inserted, all of the LEDs are covered up. Furthermore, unlike other Arduino board kits (such as the Freetronics KitTen) you are stuck with the maximum current output of 50mA for the 3.3V rail as there isn’t a dedicated 3.3V voltage regulator on board. Finally, the power switching between USB and the DC socket is controlled with a jumper and header pins between the USB socket and the 7805 voltage regulator.

Although I might have sounded a little harsh about this kit, it is relatively inexpensive, easy to assemble, and has the USB interface onboard. These are all good things. However the PCB layout could have been improved by correctly spacing the holes for the ceramic capacitors, and moving the LEDs to the end of the board so they are visible with shields inserted. What’s the point of having all those LEDs if you cannot see them…

So if you really get the urge to make your own board with the USB interface, or want to give someone some reasonable soldering practice, this isn’t a bad choice at all. Otherwise get a KitTen or save time and buy an Eleven.

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts, follow me on twitter or facebook, or join our Google Group for further discussion.

High resolution images are available on flickr.

[Note - The kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Otherwise, have fun, be good to each other – and make something!

Kit review – Current Clamp Meter Adaptor

Hello readers

Time for another kit review. Over the last few days I have been enjoying assembling a useful piece of test-equipment – a Current Clamp Meter adaptor. This kit was originally described in the September 2003 issue of Silicon Chip magazine. The purpose of this adaptor is to allow the measurement of AC current up to around 600 amps and DC current up to 900 amps. A clamp meter is a safe method of measuring such high currents (which can end you life very quickly) as they do not require a direct connection to the wire in question. As you would realise even a more expensive type of multimeter can only safely measure around ten amps of current, so a clamp meter becomes necessary.

To purchase a clamp meter can be expensive, starting from around $150. Therein lies the reason for this kit – under $30 and a few hours of time, as well as a multimeter that can measure millivolts DC/AC.

How the adaptor works is quite simple. It uses a hall-effect sensor to measure magenetic flux which is generated by the current flowing through the wire being measured. The sensor returns a voltage which is proportional to the amount of magnetic flux. This voltage is processed via an op-amp into something that can be measured using the millivolts AC/DC range of a multimeter. As the copyright for the kit is held by Silicon Chip magazine, I cannot give too much away about the design.

John’s soapbox: People may ask “hey, can you send me the schematic? I don’t want to pay for the reprinted article or buy the kit”. My answer will be no. The hobby electronics industry in this country is shrinking every day, so please support Leo and the gang at Silicon Chip by paying for a reprint or Altronics by buying the kit (it’s out of production at Jaycar). The less kits they sell, the less-inclined they will be to produce new kits.

You can purchase a complete kit from Altronics, or build one yourself by following the article in the magazine.  The hall effect sensor UGN3503 is now out of production, but according to the data sheet (.pdf), the Allegro A1302 is a drop-in replacement.

Now, time to get started. To make life easier I forked out for the whole kit, which arrived as below:

Upon opening the bag up, one is presented with the following parts:

It is great to see everything required included with a kit. And the extra battery-clamp is a nice bonus. As usual an IC socket was not included, however these can be had for less than five cents each… so I have recently solved that problem by importing a few hundred myself. The hall effect sensor is very small; considering the graph paper below is 5mm square:

The PCB was very well done – to a degree. The solder-mask and silk-screening was up to standard:

… however a few holes needed some adjustment. Doing a component test-fit before soldering really paid off, as none of the holes for the PCB pins were large enough to accept the pins, and one of the sensor socket holes needed some modification:

A small hand-held drill is always a handy thing to have around. Once those errors were taken care of, actually soldering the components to the PCB was simple and took less than ten minutes. The potentiometer VR3 needed to be elevated by 3.5mm so it would fit through the enclosure panel in line with the power switch. As I couldn’t use PCB pins, a few link offcuts from the resistors worked just as well. When soldering the components, start with the low-profile items such as resistors, and finish with the switch and potentiometer:

Now it was time to make the clamp. First up was to cut the iron-powdered toroidal core in half. All I had to do this with was a small hacksaw, so I hacked away at it for about half an hour. This process will make a mess, filings will go everywhere. So you will need some pointless rubbish to catch the filings with:

Each half of the core is placed inside the clamp. Until I am completely happy with the clamp they will be held in with blutac. A lead also needs to be constructed, with the sensor at one end and the 3.5mm stereo plug at the other. Some heatshrink is provided to cover the ribbon cable, but I recommend placing some over the solder joints where the sensor meets the ribbon cable, as such:

Next, the sensor needs to be placed between the two halves of the core – however a piece of plastic slightly thicker needs to sit next to the sensor, to stop the clamp damaging the sensor by closing down on it. Then, using the continuity function of a multimeter, check that there aren’t any shorts in the lead. Feed the newly-constructed lead through the battery clamp in order to keep things relatively neat and tidy, and you should result with something like this:

As you can see I have had a few attempts at cutting the core. The next step was to drill the holes for the enclosure, and then solder the wires that run from the PCB, run them through the hole in the side of the enclosure, and fasten the banana plugs to plug into the multimeter.

Now it was time to start calibration. There are two stages to this, and both are explained well in the instructions. This involves adjusting the trimpots which control the output voltage in millivolts, which can be affected by charge in the human body. Therefore it is recommended to use a plastic screwdriver/trimming tool to make the adjustments:

They are generally available in a set or pack for a reasonable price. The second stage of calibration involves creating a dummy DC current load using a 12v power supply, 5 metres of enamelled copper wire and a 18 ohm 5 watt resistor:

By putting 100 turns of the copper wire around one side of the clamp, putting the resistor in series and looping it into 12 volts, the current drawn will be 0.667 amps. (Ohm’s law – voltage/resistance = current). Then it is a simple task to set the multimeter to millivolts DC and adjust potentiometer VR1 until it displays 66.7 mA:

So there you have it – 66.7 millivolts on the multimeter represents 660 milliamps of current. So 1 amp of current will be 100 millivolts on your multimeter. Excellent – it works! The whole mess was inserted into the enclosure, and I was left with something that looked not terribly unprofessional (time to invest in a label-maker):

It turns out that the thick OFC cable and the battery wouldn’t be able to coexist in the enclosure, so the battery is external.

The current clamp meter kit was an interesting and satisfying kit to assemble. Originally I assumed it would be simple, but it required plenty of drilling, cutting the darn toroid in half, tricky soldering for the clamp lead, and some patience with lining up the holes for the enclosure. Not a kit for the raw beginner, but ideal for teaching with a beginner to improve their assembly skills, or anyone with some experience. Plus it really does work, so money has been saved by not having to buy a clamp meter or adaptor.

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts, follow me on twitter or facebook, or join our Google Group for further discussion.

High resolution images are available on flickr.

[Note - The kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Otherwise, have fun, be good to each other – and make something!

April 2011 Competition

Hello readers

The April competition has now closed. Thank you to all those who entered, and the winners have been announced!

Another month has passed, so time for another competition!

To enter, find the six questions that will be spread across the articles published in tronixstuff.com between the first and last day of April. When you have answers to all six questions, email your answers to competition at tronixstuff dot com with “April″ in the subject line. Then in the first week of May, I will compile a list of people with the correct answers, and randomly select two winners. Please note competition rules at end of article.

The first winner drawn will receive a full PoGa system bundle courtesy of 4D Systems, an Australian-based company who are a worldwide leader in the development and manufacture of intelligent graphic display modules.

What is a PoGa you may ask? Here is an example:

As you can see, the PoGa is an amazing piece of work. The people at 4D Systems have really put together a fun and accessible way to develop your own games. However the PoGa is a lot more powerful than the retail price would suggest:

PoGa Features:

• Single chip, low cost educational game development platform, incorporating the tiny GOLDELOX-PoGa graphics processor chip.
• Comes in an easy to build kit form with very low parts count and cost: GOLDELOX-PoGa chip, 6 buttons, Colour LCD-TFT, Battery Holder and few discrete components.
• Display: 1.44″, 128xRGBx128 resolution, 65K colour TFT-LCD (directly interfaced to the GOLDELOX-PoGa chip).
• Colours: 65K simultaneous colours.
• microSD Card Interface: Supports the PoGa-Disk which can store and load up to 512 games and other applications as well as images and video clips. It can also be used as a storage medium for data logging applications during run time.
• Sound Support: Single channel sound engine with extended RTTTL format and allows complex generation of game sounds.
• Console: Layout fashion follows most standard game consoles with 6 buttons for game and non game related application control.
• Expandable: Power and UART lines are available via 8pin expansion port.
• Battery: Supports 3 x AAA batteries for mobility (hight capacity alkaline or lithium recommended).
• Supports the high level 4DGL language platform, syntax very similar to C.
• Software Tools: Free fully integrated 4D Workshop3 IDE software development tool suite.
• RoHS compliant.

PoGa Specifications:

• CPU: GOLDELOX-PoGa chip.
• Total RAM: 510 bytes (or 255 word sized variables).
• Program Memory: 11K bytes (more than adequate for all PoGa applications).
• Speed: 12Mips (internal).
• Screen: 1.44″ LCD-TFT, with greater than 160deg viewing angle.
• Resolution: 128 x RGB x 128 pixels.
• Colours: 65K colours. Pixels arranged in a 5:6:5 colour format (Red:5 bits, Green:6 bits, Blue: 5 bits).
• Graphics:Supports all primitives such as:
  • Lines, Circles, Rectangles, Dots, Triangles
  • Chars, Strings, Text Buttons
  • Images and Video clips.
• Sprites: Up to 64 sprites can be defined, simultaneous display of sprites is unlimited.
• Sound: Single channel mono, supports extended RTTTL format and allows complex generation of game sounds.
• Console: 4 x Navigation keys, 2 x Selection keys.
• PoGa-Disk: microSD card interface that supports most uSD memory cards  for video, images, game and application storage. 2Gb and larger size cards can support PoGa file system application storage.
• Expansion: External expansion port, (RX, TX, VBat, 3.3V and GND).

The first prize not only includes a fully-assembled PoGa unit, to enable extended application and experimentation with their PoGa the winner also receives a USB programming cable, external breakout board and the GPS receiver module as shown below:

And let’s not forget the second prize – it is exactly the same as the first! Except for being the review hardware used to play… test out the PoGa here at tronixstuff. Nevertheless both winners will have a ball playing the sample games, or spending time to develop their own games, quizzes, possible GPS applications including reverse  geocaching, and so on. In the next week I will review the PoGa system in more detail and document my experience with it.

If you don’t want to wait and take a chance you can get a PoGa directly from 4DSystems, Little Bird Electronics, Sparkfun and their resellers, or Tigal for EU customers.

As with any other competition, there needs to be some rules:

• Prizes will be delivered via Australia Post regular air mail. Winners may elect for other methods upon payment of real cost;
• Winners outside of Australia will be responsible for any taxes, fees or levies imposed by your local Governments (such as import levies, excise, VAT, etc.) upon importation of purchased goods;
• If you have won a previous competition you cannot enter;
• If you have met John Boxall in person you cannot enter;
• The Judge’s decision is final with regards to any dispute;
• Entries will be accepted until 2359h GMT on 3rd May 2011.

So have fun and keep checking into tronixstuff.com. Why not follow things on twitter, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Once again, thank you to our generous competition sponsor 4D Systems!

Review – Agilent U1272A True-RMS Digital Multimeter

This is our review of the Agilent Technologies U1272A water and dust resistant digital multimeter. It’s an extremely well specifed instrument, and according to the Agilent promotional material a better alternative to the venerable Fluke 87V. We also have examined the Bluetooth module.

Initial impression

The retail box as always is impressive and well decorated. Opening it up reveals a range of items:

including the meter itself, a calibration certificate and calibration results sheet, probe set, thermocouple, quick start guide and four AAA cells. It was a little disappointing to not find alligator clip adaptors nor a carrying case. For those interested, a full range  of documentation is available here.

The meter measures 207 x 92 x 59 mm (hwd) and is quite solid, not too heavy and surrounded by a good orange non-slip rubber layer. This no doubt helps provide some shock resistance, as this unit has survived a 2.5 meter drop from my ceiling to the concrete. It is refreshing to see that the keypad is laid out in an organised way, much better than the random-looking layout on the U1250 series:

The meter

Installing or changing the the battery (four AAA cells) is easily accomplished, and thankfully the fuses are also in the same compartment. The included AAA cells are thecheaper “GP brand”, and should do for the first few months. The dust and moisture protection is evident as shown by the o-ring seal around the perimeter of the compartment:

As mentioned earlier, the U1272A is water and dust resistant to IP54 specifications – 54 meaning “protected against dust limited ingress”/”protection against water sprayed from all directions – limited ingress permitted.”.

For more information about IP ratings and what they all mean, check out this IP-rating chart.

It is possible to turn the function selector with one hand whether you have the meter standing up or laying on your desk. The included test leads are just over 1200mm in length and are rated at Cat III 1000V, 15A. Two pairs of probes are included, with 4mm and 19mm tips:

Again, it is unfortunate that alligator-clip adaptors nor probes are included – these are very useful especially to those who are colourblind and need to sort resistors or measure tiny through-hole capacitors. Furthermore, a K-tyle thermocouple and non-compensation transfer adaptor are also included:

The thermocouple’s temperature range is -20~200 degrees Celsius, however with an optional thermocouple the maximum temperature can be increased to 1200 degrees C. As for the othermeasurement ranges, they are detailed in the data sheet which you can download here (.pdf).

Furthermore there is a diode test  function, and a continuity beeper. The backlight also flashes when using the continuity function which would be very convenient for those working in a noise environment. There has been some discussion around various forums as to the speed of the continuity function, so here is a small video demonstration of it in action:

In use

Although readers would not have any problem using the meter without reading the manual, doing so will illustrate the particular features of the U1272A as well as operation of the menu system that allow various settings to be changed. These can include: beep frequency (!), backlight duration, data communication parameters, default temperature units, scale conversion values, and activating the low-pass filter available when measuring DC voltage and current.

At the risk of shortening the battery life, I extended the backlight duration immediately to thirty seconds; and set temperature units to degrees Celsius. When taking measurements that only require the main numeric display, the ambient temperature is shown in the secondary numeric display. I must admit to discovering another feature by accident, if the leads are in the current and COM terminals and you select a non-current measurement function – the meter will beep like crazy, blink the backlight and show an error message. This is useful when you’re tired and probably should be doing something else.

Measuring AC voltage provides various data upon request. Apart from the RMS voltage value, you can also turn on a low-pass filter which blocks unwanted voltage above 1 kHz.

The frequency measurement function allows the display the frequency, duty cycle and pulse-width when measuring AC or DC current or voltage. Furthermore, you can display both voltage/current and also display the frequency, pulse-width and duty cycle at the same time, for example:

In a previous article the U1272A was used to measure frequency and duty cycle, which you can observe in the following short clip:

Measuring DC voltage is straightforward, and there is also the option to measure both AC and DC components and display them combined or separately, for example:

You can also display voltage as a decibel value relative to 1 mW (dBm) or a reference value of 1V (dBv). And the dB reference impedance can also be set to fall between 1 and 9999 ohms. Another interesting voltage measurement function is “Zlow”. Using this function, the meter changes to a very low input impedance, and can remove “ghost” voltages from the measurement by dissipating the coupling voltage. This function can also be used to test if a battery is still usable, if the voltage of the battery under test decreases slowly, it doesn’t have the capacity to deliver the required voltage. However I wouldn’t put a battery under this test method for too long due to the meter acting close to a short circuit.

Measuring resistance is simply done with the U1272A, and for more precise measurements one can short the probes to measure their resistance then set a null point so your measurements will not be affected by probe resistance. There is also an Agilent feature called SmartOhm which can be used to remove unexpected DC voltages that can add errors to resistance measurements. You can also use SmartOhm to measure leakage current or reverse current for junction diodes. I look forward to spending more time examining SmartOhm.

Furthermore, one can also measure conductance (the reciprocal of resistance) which is measured in Siemens. According to the manual one can measure extremely high resistance values up to 100 gigaohms. Interesting.

Diode measurement works as expected, the standard setting displays the voltage drop across the diode. However by pressing Shift on the meter, you can use the “Auto-diode” function which forward and reverse bias simultaneously using both numeric displays. For example, measuring a 1N4004 diode produces the following display, the forward voltage and the Good/Not good result:

Measuring capacitance is also quite simple, and the manual recommends setting a null value while the probes are open to compensate for residual capacitance. Interestingly the LCD shows when it is charging and discharging the capacitor under test, using the following segments:

Temperature measurement is possible with the included thermocouple and adaptor. Note that the included K-type thermocouple is only rated for up to 200 degrees Celsius, however with an optional unit the meter can measure up to 1372 degrees C. The display can show Fahrenheit as well as Celsius. The meter also shows ambient temperature using the secondary numeric display when it is not in use with other measurement display functions. Finally, measuring AC or DC current is completed as expected, and as noted earlier when switching to another non-current function, the meter will remind you to change the positive lead.

Compared to other meters, there are a few things that irritated me slightly with this unit. The auto-ranging can be somewhat slower than other meters, especially the frequency measurement – it can take around four seconds to measure a constant frequency… my old Tektronix CFC-250 is faster than that. And the exclusion of alligator-clip adaptors and case was disappointing considering the price of the meter. However on a positive note, the meter is supplied with minimal paper documentation, and a full range of manuals, service guides and so on are available for download from the Agilent website.

Update – 14th June 2011

Turns out that many people had similar (and other problems) to myself with their U1272A. They can be solved by updating the firmware via the USB cable. Agilent will send owners of early versions with the affected firmware a free USB cable in order to fix it up. Download this .pdf file with the instructions on how to receive the cable.

Update – 20th June 2011

The USB>DMM cable has arrived and the firmware updated to v2.0. The meter now works as expected – very well. Kudos for Agilent for taking ownership of the problem and sorting it out so rapidly.

Over the last three months I have been using the U1272A and would call it a success. The dual line LCD display really is useful, as well as the low current measurement and especially the Zlow function. There is a short video you can watch that explains a few of the unique features very well. Furthermore, there is a distinct lack of fragility which gives you one less thing to worry about when looking after your tools. Finally there is also the data-logging, however this does require an optional cable. If you are in the market for a full-function electronics multimeter, put this meter on your evaluation list.

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts, follow on twitter, facebook, or join our Google Group.

High resolution images are available from flickr.

[Disclaimer - the Agilent U1272A in this review is a sample made available by Agilent Technologies via element-14]

March 2011 Competition Results

Hello readers!

As it is now April we can announce the winners of the tronixstuff March 2011 Competition. The five questions and answers for March were:

1. What year was twitter founded? 2006;
2. How many standard characters can be displayed on a DFRobot 4884 LCD shield? 84;
3. Which company manufactures the microcontroller used in our Arduino boards? Atmel;
4. Name five people from the Arduino development team - Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, and David Mellis;
5. Which IC is the equivalent to two 555 timer ICs? The 556.

Once again it was great to see all the entrants had correct answers for every question, nice work everyone. However there can only be two winners…

Congratulations to Paul G. and Stuart M. – both lucky winners of a $40 gift voucher from Little Bird Electronics.

What a month it has been. And keep an eye out for the April competition which will be announced in a few days – there are some really fun and interesting prizes up for grabs!

So as you can see you can win great prizes just for checking into tronixstuff.com on a regular basis. If you missed out this month, stay tuned as it all starts again in the next few days. Why not follow things on twitter, subscribe  for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Once again, thanks to Madeleine and Marcus from Little Bird Electronics for the prizes.