We have a ZWO ASI174MM Mini camera and are trying to use it as a guide camera using the ST-4 port. (Trying ST-4 because we are having issues with direct control/USB method).
The ST-4 port is not triggering the telescope mount for the NSEW directions. The mount does work when controlled by an older SBIG guide camera using ST-4, as well as the hand paddle.
I constructed a fixture to measure the signals on the 4 ST-4 lines. When using the SBIG camera the voltages on all four lines are about 17 V DC. When triggering a direction signal, the voltages drop to about 0.3 V. When using the hand paddle they go to close to zero (probably a mechanical switch that shorts the signal to common).
When using the ASI174MM, the voltages drop to between 1.74 and 2.07 V. This is not enough drop to trigger the mount, although intermittently they can trigger the N direction. Looking at the schematics of our DFM controller, it appears that there is a 2V threshold to trigger the mount, but this is not confirmed
It seems the ASI174MM switch contacts/circuit have too great a resistance to drop the voltage low enough for the system to work. Does anyone have an idea why this may be happening or how to get around it? Maybe the camera is defective?
