3 ms·

No analog filtering - that's how you keep things cold all the time. The frequency is either 500 Hz or 1000 Hz, I forget which (depends on Arduino type). I doub

No analog filtering - that's how you keep things cold all the time. The frequency is either 500 Hz or 1000 Hz, I forget which (depends on Arduino type). I doubt there are any critters that can tell it's not continuous.

mrob 10y ago
If I count as a critter, I can easily tell the difference by moving my eyes and seeing the phantom array effect. If you're already using resistors for current limiting then putting a big enough capacitor across the LEDs will filter them without much difference in power consumption. I have no idea if the fish will care.
- paulannesley 10y ago
  That effect drives me nuts too; but it seems to bother a minority of people. I've always assumed/guessed it's in the order of 50–100Hz; the 500–1000Hz mentioned may be fast enough to appear continuous to sensitive humans and maybe fish...
  - throwanem 10y ago
    The most usual source of that flicker these days is driving LEDs (usually in a string of Christmas lights) with half-wave rectified AC, which can be considered PWM with a 50% duty cycle over the same period as the input signal - 60Hz in the US and I think Japan, 50Hz most other places. That's slow enough to see easily; it would surprise me to learn that PWM at ten times the rate is slow enough to see at all. Looking at the code I wrote a while back to drive a four-digit common-cathode LED display (you know, a TV bomb timer!) as a clock, I find that after all the tuning I did to get rid of flicker, I ended up activating each digit for 1ms at a time. Granted, running under Raspbian this is going to flicker anyway from time to time because multitasking, but that aside, I found no PWM flicker perceptible, even at what is effectively 20% duty cycle over a 5ms period. (The decimals are implemented as a fifth "digit".) So I'm going to guess that .5KHz and up are fine for most humans. Fish I don't know about; (1) cites a flicker fusion rate between 2 and 40Hz for swordfish, but for goldfish I've no idea, other than to guess that .5KHz and up is probably fine for them too. (1) https://www.google.com/amp/amp.livescience.com/3799-fish-eyes-adjust-shutter-speed-track-prey.html?client=safari https://www.google.com/amp/amp.livescience.com/3799-fish-eye... (Sorry for AMP, but taking it off the front nets me a timeout from livescience.com. Something broken there, I'm guessing.)
    - mrob 10y ago
      In my own testing I could see flicker at 10kHz, during fast eye movement only. This has nothing to do with flicker fusion threshold. Instead it's a failure of saccadic masking. At 10kHz it's subtle enough that it's not at all annoying, but I do find 1kHz slightly annoying. The commonly used 200Hz is definitely annoying.
foobarian 10y ago
I find it useful to speed up the default Arduino PWM by changing the clock source. There are some useful details at http://www.righto.com/2009/07/secrets-of-arduino-pwm.html http://www.righto.com/2009/07/secrets-of-arduino-pwm.html . Basically you should be able to drive it up to tens of KHz. I'm not sure how far up it remains linear but works well enough for lighting. At default clock rates (clock/256) I can definitely see the flicker, especially through the lowest duty cycles.

mrob 10y ago

If I count as a critter, I can easily tell the difference by moving my eyes and seeing the phantom array effect. If you're already using resistors for current limiting then putting a big enough capacitor across the LEDs will filter them without much difference in power consumption. I have no idea if the fish will care.

paulannesley 10y ago
That effect drives me nuts too; but it seems to bother a minority of people. I've always assumed/guessed it's in the order of 50–100Hz; the 500–1000Hz mentioned may be fast enough to appear continuous to sensitive humans and maybe fish...
- throwanem 10y ago
  The most usual source of that flicker these days is driving LEDs (usually in a string of Christmas lights) with half-wave rectified AC, which can be considered PWM with a 50% duty cycle over the same period as the input signal - 60Hz in the US and I think Japan, 50Hz most other places. That's slow enough to see easily; it would surprise me to learn that PWM at ten times the rate is slow enough to see at all. Looking at the code I wrote a while back to drive a four-digit common-cathode LED display (you know, a TV bomb timer!) as a clock, I find that after all the tuning I did to get rid of flicker, I ended up activating each digit for 1ms at a time. Granted, running under Raspbian this is going to flicker anyway from time to time because multitasking, but that aside, I found no PWM flicker perceptible, even at what is effectively 20% duty cycle over a 5ms period. (The decimals are implemented as a fifth "digit".) So I'm going to guess that .5KHz and up are fine for most humans. Fish I don't know about; (1) cites a flicker fusion rate between 2 and 40Hz for swordfish, but for goldfish I've no idea, other than to guess that .5KHz and up is probably fine for them too. (1) https://www.google.com/amp/amp.livescience.com/3799-fish-eyes-adjust-shutter-speed-track-prey.html?client=safari https://www.google.com/amp/amp.livescience.com/3799-fish-eye... (Sorry for AMP, but taking it off the front nets me a timeout from livescience.com. Something broken there, I'm guessing.)
  - mrob 10y ago
    In my own testing I could see flicker at 10kHz, during fast eye movement only. This has nothing to do with flicker fusion threshold. Instead it's a failure of saccadic masking. At 10kHz it's subtle enough that it's not at all annoying, but I do find 1kHz slightly annoying. The commonly used 200Hz is definitely annoying.

foobarian 10y ago

I find it useful to speed up the default Arduino PWM by changing the clock source. There are some useful details at http://www.righto.com/2009/07/secrets-of-arduino-pwm.html http://www.righto.com/2009/07/secrets-of-arduino-pwm.html . Basically you should be able to drive it up to tens of KHz. I'm not sure how far up it remains linear but works well enough for lighting. At default clock rates (clock/256) I can definitely see the flicker, especially through the lowest duty cycles.