Post by thread:Optical encoders and Telescope Control

Philip Cowley wrote: > If I put the 2016s right by the encoders > then I have a long parallel cable... > But if I put them next to the PC then I have long leads > carrying the quadrature signals... Very noisy.... Any ideas??? The quadrature signal wires sound the lesser problem. Suggestion in order of convenience: - Twisted pairs - Co-ax - Buffer to RS485 levels (0-5V complementary) - Buffer to fibre-optics The last point made me think: encoders sense the interruption of light beams. Why not pipe these beams down fibre-optic cables to photo-transistors, Schmitt triggers, HCTL 2016 chips etc near the PC? Shotgun-section fibre-optic cable would carry two signals from one encoder. You still have to power the LEDs, but as these are near motors this should not be a big deal. Keith.

> Philip Cowley wrote: > > > If I put the 2016s right by the encoders > > then I have a long parallel cable... > > But if I put them next to the PC then I have long leads > > carrying the quadrature signals... Very noisy.... Any ideas??? Put a micro near the encoders and use one of the differrential serial links like rs485. It is good for a considerable distance, uses serial ports and is quite reliable. Walter Banks

>> The only problem I can see is the distance from the encoders to the PC... >> about 30 feet!!! If I put the 2016s right by the encoders then I hav a long >> parallel cable... Not good! But if I put the 2016s next to the PC then I >> have long leads carrying the quadrature signals... Very noisy.... Any >> ideas??? > >Put the 2016s by the encoders, put a PIC by the 2016s and use rs232 to >the PC. What I think I'll do is... Encoder -> Schmidt Trigger-> Line Driver -> twisted pair cable -> Receiver -> HCTL2016 -> I/O Card -> PC The schmidt trigger gives me a nice waveform for the signals. The line driver shifts the voltage up to +/- 12V and transmits it over twisted pair lines. The receiver brings the voltage back down to 0-5V. The I/O card drives the 2016 directly. I already have the I/O card and it works a treat! Phil