4 ms·

I threw that code in a small program. The output of that code seems too regular for it to be PDM, but then I don't really understand the code. 1 1 1 1 1 1 1 1

I threw that code in a small program. The output of that code seems too regular for it to be PDM, but then I don't really understand the code. 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 0 1 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 1 0 1 1 1 0 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 0 1 1 1 0 1 1 0 1 1 1 0 1 1 0 1 1 1 0 1 1 0 1 1 0 1 1 0 1 1 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1 0 1 1 0 1 1 0 1 0 1 1 0 1 0 1 1 0 1 0 1 1 0 1 0 1 1 0 1 0 1 0 1 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 1 0 0 1 0 0 1 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 1 0 0 1 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0

iamflimflam1 3y ago
I got ChatGPT to read the data, low pass filter and then downsample it. 1.0035971164599362 0.9085335060080786 0.9035432831636958 0.7979082616868238 0.7167128607342428 0.5957569676023409 0.49808942875852646 0.4009797804151446 0.3308973662512045 0.1857546947996519 0.07410762115348818 Here's a plot of the original data and low pass filtered: https://imgur.com/a/kCxA7XK https://imgur.com/a/kCxA7XK
- tverbeure 3y ago
  Nice! I guess I'm just bad at judging what's PDM and what's not. :-)
  - iamflimflam1 3y ago
    I think there are all sorts of modulation schemes that can be used to generate a PDM like signal. The good ones do a lot of clever things to do noise shaping and make sure it's all up the high frequencies so gets filtered out.
  - dekhn 3y ago
    Maybe I'm abnormal but I could look at the bitstream above and pretty much see that it was a falling line, although I couldn't tell it was roughly straight (I assumed it was a sine).
    - phkahler 3y ago
      It's sine-ish. It's (1-x^2)^2 with x from -1 to 1.
- dragontamer 3y ago
  > 1.0035971164599362 Ummmm... What happened here? I know that low-pass filters can "ring" and therefore have some gains in some cases. But any simple FIR digital filter won't ring like this and end up with a value above 1.00 What filter did you (erm, ChatGPT) decide to use that (1 1 1 1 1 1 1 1 0 1 1 1 1) or so averaged out to a value above 1.00 ?
  - kennywinker 3y ago
    And that, friends, is why don’t trust a language model to analyze data.
phkahler 3y ago
X simply increments with time as a 16 bit signed value so it wraps. Consider it signed value q15 so range is +/-1. Y is then (1-x^2)^2 which approximates a sine wave for brightness (0 to 1). The accumulator "a" gets this added on, but it's as 12 bit accumulator and the overflow/carry bit goes to the led. The carry is cleared on the following iteration. By the mask just before adding in y again. The rate of overflows determines the brightness. All in constant execution time too!
londons_explore 3y ago
For something that looks to a human like smooth blinking, you really need to have a sine wave, and it needs to be gamma corrected... There might be some easy way to do that, but I always just use a linearly interpolated 8 stage lookup table...

iamflimflam1 3y ago

I got ChatGPT to read the data, low pass filter and then downsample it. 1.0035971164599362 0.9085335060080786 0.9035432831636958 0.7979082616868238 0.7167128607342428 0.5957569676023409 0.49808942875852646 0.4009797804151446 0.3308973662512045 0.1857546947996519 0.07410762115348818 Here's a plot of the original data and low pass filtered: https://imgur.com/a/kCxA7XK https://imgur.com/a/kCxA7XK

tverbeure 3y ago
Nice! I guess I'm just bad at judging what's PDM and what's not. :-)
- iamflimflam1 3y ago
  I think there are all sorts of modulation schemes that can be used to generate a PDM like signal. The good ones do a lot of clever things to do noise shaping and make sure it's all up the high frequencies so gets filtered out.
- dekhn 3y ago
  Maybe I'm abnormal but I could look at the bitstream above and pretty much see that it was a falling line, although I couldn't tell it was roughly straight (I assumed it was a sine).
  - phkahler 3y ago
    It's sine-ish. It's (1-x^2)^2 with x from -1 to 1.
dragontamer 3y ago
> 1.0035971164599362 Ummmm... What happened here? I know that low-pass filters can "ring" and therefore have some gains in some cases. But any simple FIR digital filter won't ring like this and end up with a value above 1.00 What filter did you (erm, ChatGPT) decide to use that (1 1 1 1 1 1 1 1 0 1 1 1 1) or so averaged out to a value above 1.00 ?
- kennywinker 3y ago
  And that, friends, is why don’t trust a language model to analyze data.

phkahler 3y ago

X simply increments with time as a 16 bit signed value so it wraps. Consider it signed value q15 so range is +/-1. Y is then (1-x^2)^2 which approximates a sine wave for brightness (0 to 1). The accumulator "a" gets this added on, but it's as 12 bit accumulator and the overflow/carry bit goes to the led. The carry is cleared on the following iteration. By the mask just before adding in y again. The rate of overflows determines the brightness. All in constant execution time too!

londons_explore 3y ago

For something that looks to a human like smooth blinking, you really need to have a sine wave, and it needs to be gamma corrected... There might be some easy way to do that, but I always just use a linearly interpolated 8 stage lookup table...