EmonTX which resistors for step 3?

I've just begun assembling my EmonTX but it seems I've not been sent the resistors that feature on the BOM, according to Step 3 I should be using 10k 1% Resistors (brown, black, black, red, brown on blue) Resistors (as instruction below), however I appear to have received beige 10K (brown, black, orange, gold) ones, will these suffice?

"Step 3 - 10k Resistors
Add the 2x 10k resistors - they are blue and their colour code is: Brown, Black, Black, Red, Brown."

Robert Wall's picture

Re: EmonTX which resistors for step 3?

The colour of the body is not important. The tolerance - yours are 5% - will make a slight difference in the case of R14 to the initial accuracy of the voltage measurement, which you can calibrate out in the software anyway. The original kit used 5% resistors, and there are many of those in use. The only practical effect is you might have to alter the calibration coefficient a bit more.

The tolerance of the others, R1 & R8, is much less important.

mcaddy's picture

Re: EmonTX which resistors for step 3?

Ok, so ideally I would use the 1% tolerance resistors? I will ask at work to see what we've got in stock, I would have thought I should be able to source.

Robert Wall's picture

Re: EmonTX which resistors for step 3?

Ideally, yes, for the voltage monitor divider and bias chain, and for the c.t burden and bias chain. All it really means is the operating range in volts is more accurately defined, which in turn means you can in theory have a larger range in hardware and hence better resolution. In practice, it won't make a lot of difference, if any.

Let's say the input swings 800 counts given exact value divider resistors. If they're both the wrong end of 5% tolerance, you'll get approx 876 or 730 counts, if 1% it'll be 785 or 815 counts. You could be better off with the 5%, but the Law of Natural Perversity says otherwise.

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