Tinycurrent noise - Page 1
Forum section: electronics / testgear

author: AndreKR
author_rank: Contributor
timestamp: November 29, 2021, 12:45:48 am
content: I have a tinyCurrent (Sorry Dave, but the uCurrent was out of stock for ages.) but I'm having some noise issues with it and I wonder if this is the normal noise that is to be expected or if I'm doing something wrong or maybe my tinyCurrent is broken.I tested a bunch of setups with an ESP32 as the load (about 35 mA current with some spikes).When I use a BNC cable (this would be my preferred way of connecting it) I consistently get this amount of noise:With a probe I can sometimes get less noise, but I think this happens only when I have a dodgy connection to the probe (the banana plug isn't the greatest of connectors) as it seems to change when I knock the tinyCurrent or fiddle with the probe:I tried another type of connection but it's even worse (disconnected for the photo):For comparison, here's the setup with the 1 Ohm resistor I use for best performance (but higher burden voltage):After watching video MXbDf8cCsNg on YouTube I tried it with a 10 µF capacitor across the output, but that gave unusable results:

author: AndreKR
author_rank: Contributor
timestamp: November 29, 2021, 12:58:15 am
content: The noise is still there when no load is connected:With BNC as well:But when the device is off, the noise is gone:

author: Rx7man
author_rank: Regular Contributor
timestamp: December 03, 2021, 07:34:08 am
content: Dave did a great video about noise in a ucurrent, and it was dependent on what kind of load was on it. IIRC it was some differences in chip manufacturers for the same part number, and the root cause was the split rail generating op amp was unstable

author: Kleinstein
author_rank: Super Contributor
timestamp: December 03, 2021, 10:35:44 am
content: The extra "noise" when using the BNC connection may actually be oscialltion of the amplifier due to capacitive loading. The test with the large capacitor at the ouput goes in the same direction. Dave's µCurrent in some versions also had a similar problem.Chances are the circuit is missing a resistor in series with the ouput. For some OPs just the capacitance of the BNC cable ( ~ 100 pF / m) can be enough to make them oscillate.

author: AndreKR
author_rank: Contributor
timestamp: December 03, 2021, 08:25:48 pm
content: Quote from: Rx7man on December 03, 2021, 07:34:08 amCan you link me to it? I actually looked but couldn't find any that seemed related judging by the titles.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 03, 2021, 10:38:20 pm
content: The video one the µCurrent problem is #1057:https://www.eevblog.com/forum/blog/eevblog-1057-current-murphy/msg1424097/#msg1424097There is a newer video on the option to use lower noise OPs, but that would be more like a different step. Here it is likely more about an oscillation problem. A resistor (e.g. some 50 or 100 Ohms) in series to the output should likely fix the problem.

author: AndreKR
author_rank: Contributor
timestamp: December 03, 2021, 11:32:21 pm
content: Tried it with this setup: (tinyCurrent off and on)

author: Kleinstein
author_rank: Super Contributor
timestamp: December 04, 2021, 10:13:44 am
content: The extra resistor may help at the BNC connector or when connecting a higher capacitance meter. There is no need for it with a 1:10 sope probe, but it would not hurt.

author: rs38
author_rank: Contributor
timestamp: February 10, 2025, 10:57:46 pm
content: It's so sad to come across these unsolved mystery threads...@AndreKR

author: AndreKR
author_rank: Contributor
timestamp: February 10, 2025, 11:03:16 pm
content: I got rid of my tinyCurrent and got a PPK II, works much much better.