Powering PICAXE from the source to measure

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wlie

Member
I follow this forum frequently and find it very interesting and instructive.
This is my first try to get some help - sorry for my English but this is not my native language.

Question: Will this circuit work? My problem is if the PICAXE 08M can be powered by the same source as i try to measure.

The circuit should measure 3 batteries in series and light a LED if one of the batteries drops below 3V.
I do think I can make the program as I have done other PICAXE projects with some success.

Thanks in advance for any help. :)

William
 

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BeanieBots

Moderator
Welcome to the forum.

First off, we need to get some terminology correct.
You have many lines labelled as -5v but you do not show any 0v lines.
I am assuming that by -5v you actually mean 0v. ???
For example, your regulator shows +5v and -5v. That is only possible with a 10v regulator.
Your PICAXE has +5v and -5v supplies. That is 10v which would destroy it.

Also, you say "My problem is if the PICAXE 08M can be powered by the same source as i try to measure."
That is not possible, however, it is NOT what you are doing. You are supplying the PICAXE via a 5v regulator so the battery is NOT the samr voltage source supplying the PICAXE.
The PICAXE requires a fixed voltage reference (the supply) to make accurate analogue reading. The regulator supplies the reference so using a potential divider from the battery will be OK.

I hope that all makes sense.
It is very important that you understand that the regulator has 0v and +5v. There is NO -5v.
Voltages are all relative. You could decide to use 0v and -5v but you cannot have both +5v and -5v. That is a 10v supply.
 
fernando_g

fernando_g

Senior Member
As long as the voltage you are attempting to measure and the Picaxe's Vss (0V) pin share a common, it can be done.

That is the reason BB is emphasizing the fact that you should get your nomeclature straight....call it ground, call it return, call it 0V...but not -5v
 
W

wlie

Member
Of course - you are right, I should have written 0V-
All places where I have -5V are indeed ground or 0V. Also my LM78L05 can only deliver 5V.
Anyway, it looks like I have no problem with the circuit (apart from my mistake with the terminology).
Thanks for your help.
 
hippy

hippy

Ex-Staff (retired)
Note that on your Serial In download connection you have the 10K pull-down on the wrong side of the 22K. It is not meant to be a potential divider and the 10K should be nearest the PC.

Also your LED1 is upside down. Should point towards 0V.
 
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