Go Down

Topic: ShiftPWM support topic. Latest update: Schematics, high power LED's, LED strips (Read 83 times) previous topic - next topic


Hi Salsaman,

Can you be a bit more specific? then I'll try to help you.
- A schematic is easier to read than the board file
- What are you pwming? Big LED's? Motors?
- Are the shift registers running at 5v? (big mosfets often need a bit more (a small mosfet to switch the bigger mosfet).

It seems you have found a bug, thanks!
Up to 127Hz, 256 levels, 6 shift registers its all good. 128 Hz, 256 levels -> crap.
When the interrupt frequency exceeds 32768 (max of int), a variable overflows and the interrupt frequency is set to a way to low value.

I am sleepy now, more tomorrow!


Jul 26, 2011, 12:50 am Last Edit: Jul 26, 2011, 08:02 am by salsaman Reason: 1
I put together a test sketch on a breadboard with two 74HC595's driving 16 red LED's-- worked great.  I removed the RGB calls since I was just using red LED's and it worked fine.

Then I tried changing the frequency from 75 to 150, and it didn't fade, but instead flashed the LED's in an odd pattern.  Putting it back to 75, it worked great.

Should I be able to change the frequency?

The board is just for my application, sending the 595's outputs to N-channel MOSFETs to drive LED strips, not specific to ShiftPWM.  The 595 is running at 5V but I might want to run it at 3.3V later.

Update:  I posted about my successful test on my blog along with links to design files for the shift register MOSFET board.  THANK YOU ELCO!!
My Arduino blog: http://jmsarduino.blogspot.com
Comprehensive (?) Arduino-compatible board list: http://tinyurl.com/allarduinos


keep levels*frequency below 32768, until I have fixed the bug.



Go Up