High-side sensing

Ok, I've finally finished those tests for power consumption for the board that has the RF antenna on it. Only difference is, the low-side sensing wouldn't work for me. I forgot I had a serial port connection, which obviously has a ground shield on it, so not all the current was returning through the negative terminal. Leaving me with crappy results in the region of 50mV when it should have been a good solid 2V.

Anyways, for high-side current sensing, the shunt resistor needs to be added on the positive wire. However, adding this resistor on the wire will cause a voltage drop and will decrease the voltage into my device. By how much, you say? Ask Mr. Ohm and his law, (V=IR), it just keeps coming back up. So there's about 2V drop across the shunt. I needed to increase the bench supply by about 1.7 volts, thus compensating the drop and ensuring 12V input to my device. With my negative terminal grounded and all my other connections setup, I needed to sort out the oscilloscope traces. Again, I need to find the drop across the resistor to find the current consumption. I add one probe on one side of the shunt and another probe to the other side. Both probes can be grounded on the ground terminal. Now all you have to do is get the trace on the scope, subtract the differences under different operations and divide by the shunt resistance to get your current. Now I'm finally done and back to my C++ project.