# Designing a PCB that allows to measure current

What is the best way to "debug" the current in a PCB?

My (first!) PCB has a 220v->5v PS on it. I would like to measure how much current is using after the PS to monitor how far from the limits my circuit is.

To achieve that, I was thinking on adding jumper pins, to be able to attach a multimeter. Is there a better way of doing that?

• Ideally, you should be able to calculate the required current from the design so that you specify the correct size of PSU to begin with. This seems like a backwards way of designing... guess and check is not the best approach here.
– J...
Commented Sep 21, 2021 at 18:02
• If you need to measure current over time, consider using an oscilloscope, a series resistor and an opamp device e.g. the uCurrent Gold. eevblog.com/product/ucurrentgold Commented Sep 21, 2021 at 18:23

In addition to the first answer, if it is important in production you may consider the permanent addition of a TS1100 Uni/Bidirectional Current-Sense Amplifier and a good shunt resistor to give you a direct measurement of voltage across the shunt resistor and consequently the actual current, all with great accuracy. There's even a demo board that you can very quickly wire-in, and with a standard voltmeter or oscilloscope, you can measure the PS current as required.

• This is great! I am still hammering my head around it to fully understand. but it looks really good! Thanks a lot! Commented Sep 23, 2021 at 10:28

Add a low value current sense resistor in series with the output from the 5V supply, and then measure the voltage across it to determine current. In other words, do it the same way your multimeter does (it measures current internally by looking at the voltage drop across a low value resistor.)

Later on, in 'production', you can replace the shunt resistor with a shunt. (If this is important, and current margins allow, pick a standard case size so you can put a 0ohm resistor in there later.)

If you want to bring the ends of the resistor out to a connection, use a separate pair of tracks to make a kelvin connection as directly to the pads of the resistor.