Hi guys,
I am designing a automated tester at work and one of the tasks are measuring voltage across different LEDs, since this voltage is going to be 24V, I have a voltage divider (10 to 1) sitting between the subject and the Arduino.
Since there are multiple places I need to measure to voltage, I have designed my voltage divider like this:
In the screenshot, I have a couple of transistors connected to digital pins in the arduino and can control which light I want to measure, you can see the voltage divider is split into the subject (the thing I want to test) and Arduino, and they are ground respectively.
My question is that when I measure the output from the voltage divider by means of analogRead(), am I placing a load between Vout and "return to Arduino"? because if the load a tiny, the whole voltage divide will not work.
Just looking for advice and design recommendations, 
thank you
Measuring voltage across different LEDs, since this voltage is going to be 24V
24V LEDs??? Seems unlikely!
All your transistors are doing is switching ground to 'vs', which is not connected to any voltage from anywhere, so the voltage on vs will be 0V whatever you do.
If the divider is meant to take 24V and divide by 10 then the resistors are the wrong way round, Vout will be 21.6V with 24V in.
My question is that when I measure the output from the voltage divider by means of analogRead(), am I placing a load between Vout and "return to Arduino"? because if the load a tiny, the whole voltage divide will not work.
The load is tiny, with a 1k bottom resistor is is negligible. My bigger concern is whether the 10k load your divider will put on whatever you eventually connect it to will be too much.
I see, now I can see the flaws! what do you recommend in this situation? using relays? have the relays connect to digital pin and set the relays on and off from code?
Can you please elaborate on your last sentence?
PerryBebbington:
The load is tiny, with a 1k bottom resistor is is negligible. My bigger concern is whether the 10k load your divider will put on whatever you eventually connect it to will be too much.
If the load is tiny, and forms a parallel circuit with R2, wouldn't that bring the overall resistance way down?
If the load is tiny, and forms a parallel circuit with R2, wouldn't that bring the overall resistance way down?
You are interpreting 'tiny' to mean 'low resistance', which is the exact opposite of what I meant. Tiny as in not much load. For the load to be 'not much' it has to be a very high resistance, which it is.
Can you please show your complete circuit with some way to indicate the bits you need help with? Your text mentions LEDs and 24V, neither are on the schematic you posted.
