Driving Moddable Two screen backlight GPIO PWM 18 on Node-RED MCU

[rei-vilo]

Cleaning the build/tmp and build/bin sub-folders of $MODDABLE solved the issue.

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Another question related to GPIOs, this time PWM 18 in charge of backlight from Node-RED MCU.

• Configuration the RPI-GPIO node with PWM 18 shows 12 not available.

  

• Trying to access config.brightness = 75; or backlight.write(80); return errors as well.

  

• The panes Configuration nodes and Context do not list this parameter or are empty.

How to manage backlight with Node-RED?

Originally posted by @rei-vilo in https://github.com/phoddie/node-red-mcu/discussions/49#discussioncomment-4402473

[phoddie]

@rei-vilo – I'm not able to reproduce the problem using a Moddable Two. Here's a flow that changes the backlight to a random value once a second.

Flow

```json [ { "id": "bc3f7d918132436a", "type": "tab", "label": "delete me", "disabled": false, "info": "", "env": [], "_mcu": { "mcu": false } }, { "id": "71c961cee3ed80f6", "type": "rpi-gpio out", "z": "bc3f7d918132436a", "name": "backlight", "pin": "18", "set": "", "level": "0", "freq": "", "out": "pwm", "bcm": true, "_mcu": { "mcu": false }, "x": 560, "y": 900, "wires": [] }, { "id": "7290773e82e7274c", "type": "inject", "z": "bc3f7d918132436a", "name": "", "props": [], "repeat": "1", "crontab": "", "once": true, "onceDelay": 0.1, "topic": "", "_mcu": { "mcu": false }, "x": 190, "y": 900, "wires": [ [ "f214cc8f4e11160c" ] ] }, { "id": "f214cc8f4e11160c", "type": "random", "z": "bc3f7d918132436a", "name": "", "low": "0", "high": "100", "inte": "true", "property": "payload", "_mcu": { "mcu": false }, "x": 360, "y": 900, "wires": [ [ "71c961cee3ed80f6" ] ] } ] ```

I run that by updating the flows.json manually and using mcconfig -d -m -p esp32/moddable_two.

Maybe you are doing something different here?

[rei-vilo]

Thank you for your answer.

As the symptoms were not new, I cleaned the build/tmp and build/bin sub-folders.

Everything works as expected now, except PWM seems to be reversed: 100 is dark and 0 is bright.

[phoddie]

Everything works as expected now...

Great!

... except PWM seems to be reversed: 100 is dark and 0 is bright

Correct. The PWM on the Moddable Two backlight interprets 0 as full brightness and 100 as off. The Backlight in the host takes care of that automatically. But here, since you are writing to the PWM directly, you need to apply the mapping. In case you aren't aware, the Node-RED Range node can do that mapping: