USB electrical parameter tester - volt amp power watt by Fluby

Last crawled date: 3 years ago

What's this then?
I wanted to know how much current is being drawn by my Pico when running whatever
Parts
7in1 OLED Electrical Parameter Meter Voltage Current Power Energy Tester about £10
Any USB A to micro cable - but of course you could use any cable that charges things
Little bit of stripboard, and a few bits of thin cable
Solder and soldering iron
What to do
order your parts
Print the case
Clean it up - the base fit is tight - so might need sanding/scraping. Make the base fit the body first.
Cut your USB cable in half (or whatever proportions you like)
Strip 10mm of sleeving, and expose 2mm of the ends of the 4 wires on each end
Unless you have a strange cable, Red is +, Black is GND and the other two are the signals. You can check with a voltmeter
take a bit of stripboard ()or any other method you like) that will fit in the bottom of the box, and solder + and - to one end for the USB A (that's the power IN) and + and - from the micro usb to the other end (that's power OUT)
Then read the connection guide. You will find it easier to make the wires fit if you shorten the thick ones by about half before you start soldering
You will need to make sure that the +IN and the + OUT are connected together (that's the BLUE connection on the diagram), and the THICK red one to - OUT (or the polarity will be wrong)
The rest, just follow the guide.
Connect the other two USB signal wires back together with some spare bits of wire - mine was green to green, white to white but follow your colours - insulate somehow.
Insulate the thin black wire too.
Fit the tester into the top of the box (not the end with the 2 cutouts!)
turn upside down
stuff in the loose bits, then line up the wires and close the base
Test
Plug the USB A into something that is ON. The tester should show a decent voltage, and the current will be 0.
Plug the micro USB end into your Pico (or indeed anything else!) - then the current will show. If that doesn't work check the polarity of the output with a meter. After that you are on your own!
WARNING on accuracy
This works OK above 3.7 volts. When below that, I've found that the reported current falls below what's being drawn before (otherwise it would be magic!) and the other parameters with it. At or below 3.5V it stops working altogether.So for a normal USB feed it will be fine, but as the battery runs down to these levels it isn't.
On the specs (just read them after making it):
Input voltage: 4-20V
Main measurement parameters: run time, temperature, current, voltage, power, capacity, energy.
Size: 4.8 x 3 x 2cm/1.89 x 1.18 x 0.79inch
Weight:31g
Voltage range:DC0-33.00V,DC0-33.00V,DC00.0-99.9V
Current range:0-3.000A,0-9.99A,0-9.99A
Power range:0-99.00W,0-99.99W -330.0W,0-99.99W -999.9W
Energy range:0-999.99Wh,0-3300.0Wh,0-9999.9Wh
Voltage accuracy:(0.3% +2digits),(0.3% +2digits),±(0.5% +1digit)
Current accuracy:±(0.8% +3digits),±(1% +2digits),±(1% +2digits)
Capacity range:0-99.999Ah
Time range: 0-99h59min
Temperature range: -15~60°