Every month Australian electronics magazine Silicon Chip publishes a variety of projects, and in December 2012 they published the USB Power Monitor by Nicholas Vinen. Jaycar picked it up and now offers a kit, the subject of our review. This small device plugs inline between a USB port and another device, and can display the current drawn, power and voltage at the USB port with a large LCD module. This is useful when you’re experimenting with USB-powered devices such as Arduino projects or curious how external USB devices can affect your notebook computer’s battery drain.
The kit arrives in typical Jaycar fashion:
… everything necessary is included with the kit:
The instructions arrive as an updated reprint of the original magazine article, plus the usual notes from Jaycar about warranty and their component ID sheet which is useful for beginners. The PCB is quite small, and designed to be around the same size as the LCD module:
As you can see below, most of the work is already done due to the almost exclusive use of SMD components:
That’s a good thing if you’re in a hurry (or not the best with surface-mount work). Therefore the small amount of work requires is simply to solder in the USB sockets, the button and the LCD:
It took less than ten minutes to solder together. However – take careful, careful note of the LCD. There isn’t a pin 1 indicator on the module – so instead hold the LCD up to the light and determine which side of the screen has the decimal points – and line it up matching the silk-screening on the PCB. Once finished you can add the clear heatshrink to protect the meter, but remember to cut a small window at the back if you want access to the ICSP pins for the PIC microcontroller:
How it works
The USB current is passed through a 50 mΩ shunt resistor, with the voltage drop being measured by an INA282 current shunt monitor IC. The signal from there is amplified by an op amp and then fed to the ADC of a PIC18F45K80 microcontroller, which does the calculations and drives the LCD. For complete details purchase the kit or a copy of the December 2012 edition of Silicon Chip.
First you need to calibrate the unit – when first used the meter defaults to calibration mode. You simply insert it into a USB port. then measure the USB DC voltage brought out to two pads on the meter. By pressing the button you can match the measured voltage against the display as shown below – then you’re done.
Then you simply plug it in between your USB device and the socket. Press the button to change the measurement. The meter can measure the following ranges:
For an operational example. consider the next three images are from charging my phone – with the power, current and voltage being shown:
“P” for power…
current in mA
“b” for bus voltage
If you want to use the USB ports on the right-hand side of your computer, just press the button while inserting the meter – and it flips around:
Finally – here’s a quick video of the meter at work, whilst copying a file to an external USB hard drive:
I really like this – it’s simple and it works. Kudos to Nicholas for his project. You can purchase it from Jaycar and their resellers, or read more about it in the December 2012 edition of Silicon Chip. Full-sized images available on flickr. This kit was purchased without notifying the supplier.
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Today we are going to examine a small yet useful kit from adafruit industries – their XBee adaptor kit. The purpose of doing so was to save some money. How? I needed another XBee USB explorer board to connect a PC to an XBee (as we have done in Moving Forward with Arduino – Chapter Fourteen), but they are around Au$33. However I already have an FTDI USB cable, so all I really need is this kit, as it will work with the FTDI cable. So this saves me around $20.
As usual the adafruit kit packaging is simple, safe and reusable:
The components included are good as usual, including a great solder-masked, silk-screened PCB and an excess of header pins. Got to love a bonus, no matter how small:
This did not take very long to assemble at all. After checking the parts against the parts list, it was time to fire up the iron and solder away. As usual the kit is almost over-documented on the adafruit web pages. But that is a good thing…
Be careful when you place R3, make sure it doesn’t lean in towards the end of the IC too much, otherwise they could touch, or even worse – stop the IC from being seated properly:
Regular readers will know I get annoyed when IC sockets are not included with kits – but for the first time it is fine with me. If you use a socket, the IC will be elevated too much and stop the XBee from being inserted onto the board.
But apart from R3 almost stopping the show, everything went smoothly. At the time you need to solder in the 2mm header socket strips for the XBee, the easiest way (if possible) is to seat an XBee in the sockets, then into the PCB:
Once you have followed the excellent instructions, the last thing to solder is the pins for the FTDI cable. You can either lay them out flat on the PCB, or insert them through the holes. This is my preferred way, and seating the lot in a breadboard to hold it steady is a good idea:
And finally, we’re finished:
A quick check with Windows to ensure everything is OK:
And we are ready for communications. This was a very simple and inexpensive board to assemble – and excellent value if you need USB connection to your PC and you already have an FTDI cable.
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. Or join our new Google Group. 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!