Control output voltage on GPIO?

[spoonicorn]

Hi,

I want to output a constant voltage between 0.91 und 1.43 Volts on a GPIO to control the thermostat of a heater. This is just a "control voltage", so I assume it will not draw any power.

The examples I found so far only show how to power on/off a gpio (0 / 1) by using cat and sysfs.

Questions:
- To which pins do I have to connect + and - to output a controllable voltage between 0.91 and 1.43 volts
- How can I set the output voltage to a GPIO using cat + sysfs

Thanks

[Vonger]

There is no such directly output, you have to use PWM and capacitance to make this happen.

[tippy2k]

If you want to want to build a circuit, you can do what you need. First you will have to create a circuit to drop down 5vdc or 3.3vdc to the range you want. Then you can toggle that voltage on and off via a GPIO pin and a driver circuit. I don't know the exact specs for your setup but it can be done.

The most similar case to your needs would be controlling a relay via GPIO pin. The coil on a relay draws more current (watts) than a GPIO pin can give. So the GPIO pin sends low power to a transistor which will then trigger the higher power to the coil. In your case you will be triggering a lower voltage to your thermostat.

You can find plenty of examples of how to build this type of circuit. Here is as good of a place as any to start: https://developer.mbed.org/users/4180_1/notebook/relays1/

I hope this helps you,

Mark