first time here and so many questions

Using Arduino Motors, Mechanics, Power and CNC
1

First question
why is "new Topic" actually "subject"

main question.

I have tried to measure between 25 and 30 volts with and with out an external ref of 4.096v and with different styles of code , the results swing wildly . and as soon as i add the code to run a relay it gets worse.

in all cases the variation seems the same, im using a voltage divider - i cant find info to tell me can i exceed the 4.096 v on the input from the divider.

currently the divider is 30v = 5 v

this may not matter if i cant exceed 4.096 on the a0 when i use the divider and the calculations which are really simple don't reflect input.

or do i need a different ratio on the divider ?

Last question Why do people use the word Impedance when there is no alternating current.

2

25 or 30V, AC or DC? a0 on what? If Arduino, which one out of a dozen or so? Wiring diagram showing voltage divider connection to a0? Impedance applies when voltage is changing and reactive elements are involved, even if polarity does not change (AC).

3

peterr123:
why is "new Topic" actually "subject"

What do you mean by that?

4

peterr123:
First question
why is "new Topic" actually "subject"

When you click "New Topic" it asks you to say what subject your Topic is about - I don't find that confusing.

In this case a subject line of "problem getting consistent voltage reading from analogRead()" might have been more appropriate

Without seeing your wiring diagram and your program it is impossible to know what might be causing your problem.

...R

5

Well im still stuffed - ive discovered im losing voltage because of the reference voltage drooping, plus the Uno wont work on an external power supply only the USB cable ,

It does appear the reference voltage does affect the maximum full scale input voltage - can anyone answer is is the forum dead

6

peterr123:
It does appear the reference voltage does affect the maximum full scale input voltage - can anyone answer is is the forum dead

Please read the last sentence of Reply #3 and Reply #1

I don't think it is us who are dead.

...R

7

Unos work fine on external power if it is the right power, connected correctly. Voltage dividers work well provided they have sensible values and are connected correctly. Voltage references that "droop" are useless as voltage references. Reading analog values works well if it is done correctly.

You've told us nothing about any of those things in your setup and though there are many people here who are good at Arduinos without exception they're rubbish at mind-reading.

Steve

8