Voltage Divider & Voltmeter help

dc42:

xl97: So I will change out the resistors to be 4.7k & 10k respectively.. and lets me keep the draw form the 'meter' low...

but why @ a stable 7.4v from the PSU am I getting readings of 1023 from +5v - +7.4v??

My guess is that either the resistors you are using are not really 470 ohms and 1K (e.g. the one you think is 1K is actually 10k, or the one you think is 470 ohms is actually 47 ohms), or you are using one of those breadboards that has a break in the middle of the 5v and gnd rails and you haven't taken account of that break (so the 1k resistor is not connected to ground).

sorry I missed this post.. (DOH)..

is there a way I can meter my resistors? to accurately find out the values?

or I suppose I could also try to look up the color bands? (always hate that)..

any better way?

ok..

I took BRAND NEW 4.7k Ohm and a 10k Ohm resistor (fresh out of the pack)... and put them in place

4.7k in between the +Vin and +Vout

the 10k between + and the - (same as illustrated in the picks.. (but the values changed)

and I 'again' get the same results? once I turn the PSU up.. and I get to +5v.. Im already capped at 1023 analog value??

what the 'heck' am I missing here? lol..

I dont even have the LEDS in the mix or part of the project until I can fix the analog read values to be 'somewhat' near my ranges..??

I mean damn.. I only have 2 wires going to the Arduino!!! LOL GND and A5

some resistors..and two leads going to my variable PSU..

It sounds to me that you do not have the 10K resistor connected as you intend. Can you post a photo of your wiring?

If you disconnect the 4k7 resistor, do you get a stable reading of zero from the analog pin?

How about borrowing that 10K pot from your LM386 project.
Since you’re just experiencing, using a pot will make things a little easier.

Edit – corrected drawing

potscaling.JPG

dc42: It sounds to me that you do not have the 10K resistor connected as you intend. Can you post a photo of your wiring?

If you disconnect the 4k7 resistor, do you get a stable reading of zero from the analog pin?

hi-

her is the image I made of it.. (using a breadboard)

I'll see if the camera is charged (usually isnt)... and post one up of a 'real pic'..if it'll help.

@runaway_pancake-

I'll grab another 10k post I have laying around to use..

and look at your diagrams.

thanks

@runaway_pancake-

I did as your diagram outlined..and it works 'perfect'...

I even left the meter included when I hooked up the Arduino just to keep an eye-on readings.

SO goes back to.. I must be doing something wrong on the breadboard set-up?

here is a pic:

thanks for the help guys!.

Your 4k7 resistor is shorted out because you have both ends in the same row of the breadboard.

got ya!. :) thanks. I have also corrected my diagram to show my error/fix

I am now going to go back and change out the resistors to match for 8.4v input.

Thanks to everyone for your help. :D

So you've had 7.4V going into your analog pin all this time? That's not good. Does the chip feel warm when powered up now? If so, you likely blew the pin. And if not, it may be partly damaged and fail on you eventually.

"is there a way I can meter my resistors? to accurately find out the values?" Yes, just measure them with your multimeter. You have gold bands on the resistors? I think that's 10% tolerance (maybe 5%, I'm not sure which). If you know the actual values, you can use that in your math for more accurate results.

I would just add: Ohmmeter your resistors out of circuit, [u]Never[/u]* put an ohmmeter on a live/powered circuit.

(* For your meter's sake.)