How to boost a weak signal from digital calipers

Hey all- This is not directly related to arduino but I thought you all might have some good insights.

I'm trying to read and control a cheap pair of digital calipers from an off-the-shelf remote readout. The readout works fine at 6' (the length of the provided cable). I spliced in 40' of additional cable (18ga). The display only works occasionally with the splice. All the connections are good. Aside from using bigger conductor, any suggestions? Shielded cable? Boosting the signal? (if so, how?)

Thanks! Cory

That is a long way for a digital signal.

Three things to try in order:- I would suggest a pull up resistor of 1K at the arduino end. Also some extra decoupling capacitors across the supply at the calliper end.

Otherwise you need to feed the signal from the calliper into the base (through a resistor) of a transistor, with emitter to ground and the collector to the long wire. At the arduino end have a pull up resistor to +ve.

If that doesn't work then the same arrangement but with the pull up to 12V and a transistor to protect the input of the arduino.

Any idea as to how the signal gets sent from the caliper to the display?

Parallel? good to about 10 feet.

Serial? TTL converted to RS-232, 30-150 feet @ 9600 baud

What interface do you you use between the calipers and the micro ?

The standard caliper output swing is only 1.5 V or less and the battery +ve is connected to ground.