Deciding on a DMM, USB logic analyser, and power profiler.

I have two logic analysers which I recomend:

This one

https://thedebugstore.com/products/zeroplus-lap-c-logic-cube-analyser-uk

and this one:

https://thedebugstore.com/products/zeroplus-lap-c-pro-logic-protocol-analyser-uk?variant=40764571812029

I've found them to be way better than any scope based logic analyser.

For power measuring I've used a Joulescope but don't much like it - I've taken to making my own (1 op-amp - a P channel MOSFET and some Rs and using with a low noise scope.

Might be your best bet is to go for a Fluke that's in your price range - they last forever and are portable - just checked and the nice ones are too pricey.

SO my advice would go for a cheap handheld and save up or buy a secondhand bench top DMM.

The Siglent SDM3065X almost gets into yur budget but I haven't used one and I'd be a bit reluctant to spend that much on a  Chinese brand DMM.

The Keithley DMM6500 is great but expensive.

If you want to use your DMM to measure power you will need one with selectable DC time contants and ideally fast (20kHz+) sampling. Or use a scope.

If you want the ciruit of my current measuring amplifier let me know and I'll post it here.

MK

Hi Michael,

I’m curious what you use for current measurement 

Hi Michael,

I’m curious what you use for current measurement 

This is the circuit I'm using. It measures high side current through R100 and drives the same current throught R104, R105 and R106.

It was extracted from a bigger design so apologies for the odd net names.

With the values shown you get 10mV per mA

The OPA192 has a very low offset and rail to rail IO. It needs at least 5V to work. V5F is the supply for the op amp and could be increased if you needed a higher supply voltage to the DUT. V5F should be at least 0.5V above SW_3V3_PWR.

C100 sets the rise time of the amp to about 22us, you can speed it up (or slow it down) by changing C100.

You can look at dynamic currents with a scope across R106 aor measure average current with a DMM so long as it has a long enough integration time.

I built my first version of this on stripboard and it worked fine.

Q100 is a tiny PMF170XP - if you increase the supply and run at high currents it will fry - but larger parts will work.

Its not a good design for battery power testing because it doubles the current drain of the DUT.

MK

Thanks, I am going to try and set aside some time to model it