I have been inspired by "Laser Developer" and have made a DMTD (Dual Mixer Time Difference) measurement system using two propeller boards.
One board is simply a generator. It generates two 1MHz square waves that are 90 degrees (250nSec) out of phase.
These two signals are fed into a second propeller board that will sample the two signals at 1MHz. But because the two boards have seperate crystals there will be (should be) a small frequency difference between the two boards. In my setup the difference between the two was 19ppM (19Hz @ 1MHz). There MUST be some difference between the two for the system to work.
First the two signals are interconnected using short wires of the same length. The system can then be zeroed by pressing a key in PST. Then one of the short wires is replaced with a long wire to be measured. The system will measure the actual phase delay caused by the time it takes the signal to travel the length of the wire being measured.
I have hacked this up in PropBasic, but I want to re-write it in spin to make it more generic for Propeller users.
I've tried this on two different setups (one at work and one at home) and it seems to work. I used a 19 foot piece of wire and the system said it was 22 ft (but I don't think electricty flows at exactly 1 ft per nSec).
If you want to try this out, I used P0 and P1 for the signals (don't forget to connect the grounds together too).
Let me know if you try this. If there is enough interested I'll do a little write-up for it.
P.S. If you prefer there is a spin version posted further down.