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Autoguide Interface for Celestron Advance Series Mounts



The Autoguide Interface circuit diagram is shown here. There are several point that the user must be aware of. In the K3CCDTools guiding software there are five outputs (RA+, RA-, RA Stop, DEC+, and DEC-). However, The Celestron Autoguide interface uses only four signals (RA+, RA-, DEC+, and DEC-). For proper operation, the K3CCDTools RA Stop output is mapped to the Celestron RA+ input. The K3CCDTools RA+ output is not used. All other mappings are like name output to input.

One could use this circuit for the standard PISCO interface found on Astrosnap and Astrort CCD plugins but the CD4094 pins must be reconnected differently as shown in the table below:


CD4094.... Output  CD4094.... Pin K3 Function.... Celestron K3.Interface PISCO Interface.... Celestron PISCO.Interface
Q1 4 RA+ not used RA+ RA+
Q2 5 RA- RA- RA- RA-
Q3 6 RA Stop RA+ DEC+ DEC+
Q5 14 DEC- DEC- not used not used
Q6 13 not used not used not used not used
Q7 12 not used not used not used not used
Q8 11 not used not used not used not used


Also, the diagram shows +12V coming from pin 1 of the Celestron autoguide port. This voltage is NOT PROVIDED in the Celestron Advanced Series autoguide port. One can take the Celestron mount covers off and make this modification to the internal PC Board on the mount. Please be aware this may void your warranty with Celestron. Or as shown on the diagram, use an external 12 V connection to the 12Volt supply for the mount.

Warnings and Notes:

1. Do not make a connection to pin 1 of the autoguide port if you intend to use an external connector for 12 Volts. It is best to not introduce this voltage into the mount control system in this manner.

2. If you use an external connector for 12 Volts and this 12 Volts is the same used to power the Advanced Series mount, it is recommended that  you do not make the negative connection on the external connector and instead derive the negative leg from the autoguide port only. There is a polarity reversal protection diode in the negative lead of the Advanced Series mount. Making a second negative leg connection with the external connector for 12 Volts bypasses this diode and its protection. It may also make the guiding signals noisy since motor current will essentially go through the autoguide port.

3. I have been unsuccessful with this interface on Dell Laptops running Win2K. I understand Win2K works with other Laptops. I have had no trouble with this interface with ME or Win98 on at least 3 other PCs.

4. I have used the CD4094 Shift Register instead of others who have used the 74HCT595 Shift Register. The CD4094 is generally more available and can operate between 5 and 15 Volts so no 5 Volt regulator is needed as with the 74HCT595. The CD4094 however requires a fast transition clock pulse. The 2N3906 was added for improving pulse rise and fall times. The CD4094 would not function properly with the opto coupler alone since the clock pulse rise and fall times were too slow.



Here are some images of this circuit built into a project box.


All images and content remain the property of Jim Thommes - copyright 2003, 2004

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