LCD brightness control screwed up on Mega 2560

Other Hardware Displays
1

hi all

I'm using the DFRobot LCD Keypad Shield. Pin 10 controls backlight brightness via analogWrite()

I was using MsTimer2 but it doesn't work on the Mega 2560, so I've switched to FlexiTimer2 (latest version, not the one on the playground) which does work on the Mega 2560.

Problem.. analogWrite() on pin 10 doesn't work! any value other than 255 results in minimum brightness.

This Mega 2560 is not a "real" Arduino (it's made in China and came from ebay) so I'm not sure if this misbehavior is due to the China thing, or there really is some interaction between PWM on the Mega 2560 and FlexiTimer2..

The exact same code works fine (and controls the LCD brightness properly) on a (real) Arduino Uno.

2

In the mstimer2 release notes (which flexitimer2 is based on):

Note that the PWM signals created by Timer 2 will become unusable while Flexitimer2 is using Timer 2.

On Arduino Uno, those are pins 3 and 11.

On Arduino Mega, those are pins 9 and 10.

I bet the analogWrite() will work just fine if you don't turn on the timer code.

On the mega, looks like you will need to pick a different pin besides #10 to use with
flexitimer2/mstimer2.

--- bill

3

Yup. Confirmed that with the FlexiTimer2 maintainer. I've updated the Playground docs to reflect this.

Thing is the DFRobot LCD Keypad Shield uses pin 10 for backlight control, and this can't be changed. Doh!

4

But I believe that you can still get on/off control of the backlight on pin 10.
You just won't be able to dim with PWM and use Timer2 with mstimer2/flexitimer2 at the same time.

The 2560 has more timers and the library could be altered to use another/different timer
but that would be more work than just limiting the backlight control to on/off.

--- bill