Circuit/device not working properly with meter in series? - Page 1
Forum section: electronics / general

author: XOIIO
author_rank: Super Contributor
timestamp: November 11, 2015, 04:23:38 am
content: So, this is an interesting issue, I got a bluetooth module to make some wireless headphones (probably will make a thread on that at some point, hopefully I'll have time before I go on my trip), anyways, something interesting has happened.So, the bluetooth receiver works flawlessly normally, starts up fine, pairs, plays music, etc. However, when I put my multimeter in series with the circuit to measure the current it is using, it shows 84 milliamps, and it does not start up at all, though occasionally it does flash the led and play a few of it's start up sequence tones, but doesn't go beyond that.When I measure a green LED at 3.5 volts and other lower voltages, it shows the sort of current draw you would expect, varying between 5 and 25 or so milliamps, with the same brightness as without the meter in series.I had measured the current draw before, with just the board itself being powered, and it started at 30 miliamps, then dropped to 15 miliamps afterwards.My question is, what on earth could be happening? The only differences to the circuit are an LED and resistor connected to the pin showing the status of the device, and the speakers. I removed the speakers and the indicator LED, and still get an 84miliamp current draw.I've triple checked all the connections with continuity and with resistance in case there was some small strand of solder that connected them ever so slightly, but get nothing there either. It's really a head scratcher, I mean, the only thing I can think of is a teeny tiny bit of solder bridging two of the connections on the board together, but I can't find it with my meter, and for a solder connection to only draw 50-70 milamps, it would have to be ridiculously thin, I don't even know if you could get a connection that thin in the minute amount of space between the connections.This is the board itself, as you can see the gap between the pads/connections is extremely tiny.I think I'll run an exacto knife between pads/connections a couple times just to be ultra sure, I don't know what else it could be.I just wish I had a clamp on ammeter to double check that it's not the meter somehow (though I've never had problems with it before, and it measures the LED just fine)

author: Stupid Beard
author_rank: Regular Contributor
timestamp: November 11, 2015, 04:35:48 am
content: Its the burden voltage of your meter:Dave has done videos on it before as well, but that one was easier to find quickly.Edit: Oops, that was the wrong video.

author: XOIIO
author_rank: Super Contributor
timestamp: November 11, 2015, 04:49:39 am
content: Ah, interesting, I've never encountered this before, I guess it's just a mix of the right variables/conditions for it to show up.I'll have to think a way around it, maybe just pick up a super cheap multi-meter from princess auto to check the voltage after the meter, I have a lambda dual output power supply but that won't work very well down at these levels (won't be able to accurately see what it's drawing)

author: XOIIO
author_rank: Super Contributor
timestamp: November 11, 2015, 04:55:28 am
content: Ah man seems dave talked about it in his second video, 35 seconds and I've already had a good chuckle.