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PICList Thread
'Optical encoders and Telescope Control'
1998\01\28@083745 by Keith Howell

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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.

1998\01\28@094324 by Walter Banks

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> 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

1998\01\28@101553 by Philip Cowley

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>> 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


'Optical encoders and Telescope Control'
1998\04\05@120112 by Keith Howell
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Hi PC.

Just a follow up note to see how the scope automation is going.

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