George Observatory 36" Encoders

This project came from a desire to improve the encoder resolution on the George Observatory 36" telescope and provide an encoder mounting that was compatible with standard planetarium software such as MegaStar and The Sky. The existing RA encoder is mounted on a dial drive shaft that is stationary while the telescope is tracking. Standard RA encoder interfaces assume the RA encoder is turning any time the telescope is tracking or otherwise moving in RA. Since observatory funding is usually at a premium, this project was built around a Basic Stamp microprocessor and a USDigital LS7266R1 encoder/counter interface chip. Total cost of materials was less than $150.
The original encoders were left in place so the Point-N-View program would remain functional.
New mounting brackets were designed for the new encoders. The new encoders use rubber tired wheels that are turned by friction with the RA and DEC telescope drive gears. The exact final encoder resolution was determined using stars.
The new interface had problems initialy with spurious resets. This was traced to the ATN line into the Basic Stamp carrier board. The ATN line is only used by the programming software to put the processor in program mode. The pin was pulled to ground with a 3.3k ohm resistor and filtered with a .1uf capacitor.