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edlins / libPCA9685

superfast PCA9685 library for Debian platforms. developed on Raspbian on a Pi B+.
MIT License
13 stars 8 forks source link

LEDs never fully turn off #76

Open jmagers opened 5 years ago

jmagers commented 5 years ago

I'm using LEDs with the PCA9685 as a current sink and can't get them to fully turn off. LEDs are very dim but still on.

I would expect that when using PCA9685_setPWMVals with onVals all set to zeros and offVals all set to 4095 then all LEDs would be completely off.

After some googling I found that there is a special value for this chip, 4096, for setting a channel to completely off but could not get this to work either. https://forums.adafruit.com/viewtopic.php?f=22&t=52817

edlins commented 5 years ago

Hmmm, unfortunately I'm using the PCA9685 as a source to drive MOSFETs so I can't easily recreate current sink issues without building a new circuit. An unsigned int off value of 4096 should set the off low register to 0x00 and the off high register to 0x10 which is full off. You can enable _PCA9685_DEBUG mode to confirm the registers are getting these values. If the correct values are confirmed I would take a close look at your circuit design and see if there is any way current could be sinking elsewhere.