I am wanting to modify an existing battery powered device, to switch it on and off using a raspberry pi. To do this I want to make a transistor relay circuit. However, I need to know the current of the circuit and it is here that I am running into problems.
I have tried measuring the current whilst connecting one probe to the battery and the other to the battery terminal as advised by a friend (I am a compete noob to electronics), but the device won't switch on.
I have tried to connect a resistor between the battery terminal and the battery, but the device briefly lights up, for just an instant and then shuts down.
I have tried measuring the current over the resistors on the board, but they are very small smd resistors and I can't get a reading.
Can anyone advise on the best way to measure the current?
I am using a fairly cheap digital multimeter. I have a few spare 100ohm resistors.