emontx voltage check



Following the build guide, I'm just after doing the voltage check and got above 3.3V.

Between GND and VCC: 6.3V

Between GND and PWR: 10.4V

This would have been my first time soldering but I think I done a pretty good job and there are no shorts.

Also in step 3 of the build guide, it says to add 2 x 10k resistors that were blue with colour code: Brown, black, black, red brown. I had received a different set though. These were not blue but the same colour as the rest with colour code of gold-orange-black-brown...but I believe these are the same so I wouldn't think this makes a difference.

I don't know if this matters either but one of the resistors may be facing the wrong way around and I had to desolder one of the electrolytic capacitors to change direction. 

Where do I go from here? I'm not very electronic savy so I would be grateful if someone could give me some advice on what to check.

I can then proceed to add the RFM module, the antenna and the ATmega328.

Thanks in advance.


Robert Wall's picture

Re: emontx voltage check

You appear to be putting a seriously high voltage on your emonTx. How are you powering it? The usual way is either with a plug-top USB power supply and lead to the USB connector, or via the programmer and your computer's USB. Both should give you nominally 5 V and no more than 5.25 V anywhere on the board.

The other possibility is your meter is faulty. What voltage do you measure across a 1.5 V battery? And your car's 12 V battery?

Don't continue with your build until you have resolved this.

Don't worry which way round the resistors are - it doesn't matter (I just looks more professional if they all face the same way!)  It also doesn't matter for the small-value ceramic capacitors. It does matter for most of the other components.

Your 10 K resistors are fine. The ones you have are 5% tolerance (the last colour - gold - is the tolerance, you read it from the wrong end, the one described was 1% tolerance).


acousticer0111's picture

Re: emontx voltage check

Hi Robert,

I'm just powering it through the mini usb port on the emontx which is connected to my laptop.

I checked a 1.5V battery and it showed 2.4V so obviously it must be the digital multimeter I'm using. I failed to mention that the black lead had come out of the probe - surely that must be it. I have like a DIY fix on it at the moment but maybe I need a new set of probes.

Robert Wall's picture

Re: emontx voltage check

I think you were measuring pick-up from somewhere.  You must keep your test gear in good order, otherwise you're lost. But there's a serious warning here: What would have happened if you had tested a live mains circuit and your meter had shown it was safe? At best you could have had a nasty surprise; at worst, a fatal shock. Always check your equipment before relying on it. You could have proved your probe was faulty by bringing the two probes together and measuring Ohms - anything other than zero and you have a problem.

acousticer0111's picture

Re: emontx voltage check

Oh of course, yes I know. I did borrow it off a friend though and considering this was only a small circuit board I thought I would just give it a go to see.

Thanks for advice anyway Robert.

Hopefully it will be okay when I check it again, otherwise I might have to call on your help again;)

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