Is it possible to re-assign EV3 sensor pins from inputs to outputs using something like Arduino's pinMode()?

[SoftwareArkitekt]

To start: I only want to drive LEDs (not motors) via the sensor ports. Specifically, EV3 -> NXT 9V converter -> Power Functions Extension -> Power Functions Light Cable. While I have seen this question once or twice in other places on the Internet, I am trying to get at something a little more specific.

On motor ports (which I have reserved for actual motors), Pin 1 is positive PWM (+9V?) and Pin 3 is GND, however on sensor ports Pin 1 is mapped to Analog Input and Pin 3 is GND. I have read that pin 1 of Ports 1/2/3/4 of the EV3 are connected to GPIO pins on the processor; is there a way to tell the EV3 brick to use them as voltage outputs instead of analog inputs (either through a built-in function or through the Linux subsystem)? Thinking to other microcontrollers such as Arduino-based systems, pins usually have the capability to perform multiple functions depending on whether you initialize them using pinMode(A0, INPUT_PULLUP); for an analog input, or pinMode(A0, OUTPUT); digitalWrite(A0, HIGH); for a digital output.

I suspect what I am attempting is possible, but whether or not 1) the functions/registers for this are exposed to the user, and 2) if the supporting circuitry can provide steady voltage is another question. According to EV3Dev Pin 1 of ports 1/2/3/4 map to the ARM1808 processor pins GPIO 8-10/GPIO 8-12/GPIO 6-4/GPIO 8-9 respectively, and according to page 21 of the Technical Reference Manual from TI all GPIO pins are capable of multiple modes of operation.

If this is not possible, my fallback plan is to splice a custom cable to use Pin 4 (+4.3V) of the sensor pins to provide a constant output to LEDs.

Thanks in advance.

[laurensvalk]

Some sensors use the 9V battery supply on pin 1 or 2 (I forget which one). If the other is connected to ground (I don't remember, but you could look this up) it might be technically possible. It would only be on/off though, so there is no PWM for brightness control.

And you would still need a way to activate this sensor mode. If I recall correctly, the Ultrasonic Sensor makes uses of this. To verify, you could attach it and measure the voltage across pins 1/2.

If this is not possible, my fallback plan is to splice a custom cable to use Pin 4 (+4.3V) of the sensor pins to provide a constant output to LEDs.

If you did it this way, you'll be able to toggle the light on and off by setting the sensor mode to analog, and toggling between active/passive sensors.

[SoftwareArkitekt]

Thanks for the input; I didn't know that the sensors also used 9V. Grounding pin 1 or 2 sounds like a physical workaround to the issue, but as you said the ability to control brightness would be good. I'll do some testing on this later - I am still attempting to find a software override if possible.

[dlech]

You can use either Pin 1 to supply battery voltage or Pin 4 to supply 5V to power the LED. Battery voltage would be better if you have lots of LEDs as the 5V supply is shared with other things on the EV3, like USB and the analog inputs. You can use Pin 3 as the ground for both of these. Pin 2 cannot be used as ground.

The easiest way to turn the power supply on on pin 1 is to put the port into "other-i2c" mode. Putting it into any other mode will turn the supply off.

[SoftwareArkitekt]

I'll give the i2c mode a shot. I know laurensvalk mentioned no PWM capabilities would be available - would there be a way for me to add in something custom after the fact, or is that a limitation of the hardware itself not being able to switch on/off fast enough?

[dlech]

Correct, PWM is only available on the motor ports, not the sensor ports. You could probably switch the power on a sensor port on and off fast enough some of the time, but not all of the time. Since Linux isn't a realtime OS, there will be occasional flickering while the OS is busy doing something else.