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Finally got the ST4 autoguiding working with Phd, an St80 guide scope and a QHY5.
A control picaxe monitors the state of the 4 ST4 pins from the QHY5 optocoupler outputs and sends appropriate RA corrections to the picaxe controlling the stepper via I2C.
Since the picaxes run at 64Mhz, corrections are instant.
I added LED's as well so I can visually see when guide pulses are sent.
Each correction pulse changes the tracking speed by 0.5x for the duration of the pulse to reduce or increase the tracking speed.
I was only able to test it for a minute before the clouds rolled in but the Phd RA graph was within one division of the centre line and I got perfectly round stars. So its looking promising.
I mounted the ST80 on the opposite side of the QHY8 and focuser, so it acts like a counterweight.
Just waiting for the skies to clear and will try it again.
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