So I was on the Gen7 forum topic with Traumflug and we were both wondering why all the firmwares seem to be moving to high frequency PWM for heater control. This tends to make selection of FET's more difficult and more expensive, not to mention all the electrical noise you are injecting into the system using high power high frequency signals. So the question is what are the benefits to kHz PWM? Would PWM at a few tens of Hz accomplish the lions share of stabilizing temps without the baggage for the electronics designers? https://reprap.org/forum/read.php?147,80433,80433#msg-80433 Fri, 14 Aug 2026 08:52:36 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?147,80433,81505#msg-81505 https://reprap.org/forum/read.php?147,80433,81505#msg-81505
100Hz cycling should not be a challenge to a FET.

BTW I also read the temp sensor at 100Hz but average it over 100 samples (1s) for M105 output. The PID runs at 100Hz because it's possible to choose reasonably scaled constants at that speed and the net effect averages out the noise in Gen6 just like using the averaged value but without feeling like I have to verify the stability of the double integrator.]]> BenJackson Firmware - experimental, borrowed, and future Wed, 20 Apr 2011 18:40:55 -0400 https://reprap.org/forum/read.php?147,80433,80581#msg-80581 https://reprap.org/forum/read.php?147,80433,80581#msg-80581 -------------------------------------------------------
> Sounds good, and is the PID control frequency also
> configurable, or would that be a firmware change?

find next_read_time in temp.c:220. This controls how often sensors are polled, in 10ms units. It defaults to zero for thermistors. Set it to 100 for 1hz read. PID is calculated once every time the sensor is read, so this also controls PID frequency.]]> Triffid_Hunter Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 21:28:06 -0400 https://reprap.org/forum/read.php?147,80433,80579#msg-80579 https://reprap.org/forum/read.php?147,80433,80579#msg-80579 Traumflug Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 21:04:50 -0400 https://reprap.org/forum/read.php?147,80433,80574#msg-80574 https://reprap.org/forum/read.php?147,80433,80574#msg-80574 bryanandaimee Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 20:07:15 -0400 https://reprap.org/forum/read.php?147,80433,80572#msg-80572 https://reprap.org/forum/read.php?147,80433,80572#msg-80572 -------------------------------------------------------
> would it work to sample at say 1 or 2 Hz
> and then run the PWM at 10 or 20 Hz?

yep sure that should work fine, let us know how it goes :)]]> Triffid_Hunter Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 20:02:40 -0400 https://reprap.org/forum/read.php?147,80433,80570#msg-80570 https://reprap.org/forum/read.php?147,80433,80570#msg-80570
1. keep the 100 Hz sampling rate but time average the samples down to say a few Hz and run the PID at that frequency. The PWM could then be run at 10x that or a few tens of Hz.

2. Drop the sampling rate down to a few Hz and run 20 or 30Hz PWM.

comments?]]> bryanandaimee Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 19:29:57 -0400 https://reprap.org/forum/read.php?147,80433,80460#msg-80460 https://reprap.org/forum/read.php?147,80433,80460#msg-80460 nophead Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 04:54:13 -0400 https://reprap.org/forum/read.php?147,80433,80453#msg-80453 https://reprap.org/forum/read.php?147,80433,80453#msg-80453 Triffid_Hunter Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 03:27:15 -0400 https://reprap.org/forum/read.php?147,80433,80433#msg-80433 https://reprap.org/forum/read.php?147,80433,80433#msg-80433 bryanandaimee Firmware - experimental, borrowed, and future Tue, 12 Apr 2011 00:03:22 -0400