Ok I have a very specific #electronics question... I want to control a #telescope mount from an Raspberry through the ST4 interface. This interface is very simple, you just have to "short" one of the 4 lines to the common ground to send the signal to move in that direction. On my mount I've measured 3.3v. On the interwebs everyone does what I want to do with optocoupleurs, but I don't have those at hand. In my mind I can achieve the same thing using transistors. Am I going to break something?
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@corpsmoderne electrically probably is not a problem, I would consider why other people use an Arduino to do it. It is easier to achieve precise timings on a microcontroller. This is why most of the 3d printers use a microcontroller to direct the steppers, not a microprocessor with a full OS. Just a warning if you have not thought of it.
@sam_asensio I don't really need "precise" timing for this application. My gut feeling is that I won't adjust the signals more than 10 times / sec, tops. For the real deal people use a laptop connected to a dedicated guiding camera which has a dedicated ST4 port to control the mount, and I'm not even sure which device does what exactly in this setup 😅 . I'm going for the simpler, cruder solution here.
@corpsmoderne The typical use for optocouplers is to isolate two systems electrically. Reasons include safety and noise reduction. But since a mount only operates motors, I don't see a huge need for isolation. Does the mount manufacturer have any useful information?
@corpsmoderne that looks its probably going to be fine. Assuming the PCB annotations are right then this is some sort of pull up in the scope mount, any old transistor will be fine. Or maybe an ULN2003/2803 driver.
Avoid making ground loops that you might get if you power the raspi from the same supply as the scope mount (but connect the grounds, of course)
@corpsmoderne depending on how disposable you consider the raspi you can do it without the transistor buffers even.
@idiot you mean, connect directly the GPIO to the signal wire, let them float by default and set them to off to activate a direction? Yeah I'd like to not fry the PI, I may be ok sacrificing a couple of GPIO pins though 😬
@corpsmoderne yeah set them open drain and pull down as needed.
A low voltage CMOS/TTL open drain buffer or inverter would protect the raspi too, depends on what you have in your junk box.
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