I have the following scenario:
There are two halves to my system -- one at 12V with analog circuitry (shown in drawing), and the other at 5V which includes an arduino micro (off dwg to right separated by 50 ft of wire). They share a common ground and are battery powered. At the 12V side, I sits an element that needs tested for continuity (I must detect open, short, or pass). Passing means the resistance is loosely within target range (I don't have to measure it's value with any great accuracy).
The drawing is based on a 4-wire (Kelvin) resistance measurement (hoping the low current flow through the long cable would minimize losses in measurement). Since the voltage is so small, I would think putting an amp between the DUT and micro controller might work, but I can't send more than 5V to the arduino and the range of possible voltages for the DUT doesn't let me amplify them linearly, either. Ideally, I'd want an system in the middle that would do the measuring and output as follows:
Rules:
There are two halves to my system -- one at 12V with analog circuitry (shown in drawing), and the other at 5V which includes an arduino micro (off dwg to right separated by 50 ft of wire). They share a common ground and are battery powered. At the 12V side, I sits an element that needs tested for continuity (I must detect open, short, or pass). Passing means the resistance is loosely within target range (I don't have to measure it's value with any great accuracy).
The drawing is based on a 4-wire (Kelvin) resistance measurement (hoping the low current flow through the long cable would minimize losses in measurement). Since the voltage is so small, I would think putting an amp between the DUT and micro controller might work, but I can't send more than 5V to the arduino and the range of possible voltages for the DUT doesn't let me amplify them linearly, either. Ideally, I'd want an system in the middle that would do the measuring and output as follows:
- Pass: 0.005-2V -> 2.5V-ish output
- Open circuit: Anything higher than passing V -> 5V output.
- Short circuit: Anything less than passing V -> 0V output
Rules:
- No more than 50mA through the DUT (preferably no more than 25mA)
- Only one available line (besides ground) to the aruduino (no two signal solutions, hence using the A/D for three states).
- I can add a 5V regulator at the 12V side if needed but the fewer parts, the better.