J14 - Power Measurement Header?


(Anthony C) #1

I’m working on measuring the power consumption of the HiFive Unleashed board. I’d planned on using a custom circuit, but then I noticed that there’s a header on the HiFive Unleashed board labeled “J14” and “POWER MEASUREMENT”, directly under the GPIO header. However, I’ve searched through the schematics and documentation, and I haven’t found anything discussing the header’s use.

Is this a documented feature? If so, did I miss something? And if not, is there any guidance on how to use the header to measure power?

Thanks!


#2

J14 is just an organized set of test points for the sense resistors on the board. If you look at the silkscreen, you’ll see that one side is the Positive side ( P) and the Negative side (N) and you’ll see the label for each rail.
For a particular rail,

  1. Connect the ground of your differential probe to the Ground on J14
  2. Connect the positive side of your probe to the P side of J14
  3. Connect the negative side of your prove to the N side of J14

Now you can measure the voltage across the P and N for a particular rail, divide it by the sense resistor value, and you’ll get the current for the rail at the time of measurement. Also note that the sense resistor may be different for each rail.

image

The pin pitch on the connector is 1.27mm so it will be easier to plug in if you make a cable/board with the correct pitch. Also, since you’re dealing with voltage rails, be careful as to not damage your board.