ATX PS On Pin: Pulse a Heartbeat Signal for External Watchdog?

JustDave

All you really need is a 5v USB wall charger to power the duet, and an external mosfet board for Psu DC supply. Or use an ssr to control the AC side to the psu. Both can be controlled by the ps on pin. Getting the right functionality for psu off in the event of a heater abnormality I'm not sure about but it can't be that hard to do.

This is all good and well as long as the processor is still capable of controlling the PS_ON pin output. But, the original intent of the this post was to account for the case where the Duet board processor has frozen up and unable to change the state of the PS-ON pin, or take any other action to reduce the risk of a dangerous situation.

dc42

If I decide to add firmware support for a heartbeat on PS_ON, what frequency would you want, and what duty cycle?

DjDemonD

JustDave, makes sense and its a novel approach.

JustDave

Frequency of one cycle per second is sufficient, and a duty cycle of 50% is fine.

JustDave

@dc42:

I think the problem is that the M81 command waits for all movement to stop before it executes.

Instead of using M80/M81 and the ATX power pin, I suggest you use one of the pins on the expansion header, then you can use M42 commands to set it low and high. See https://duet3d.com/wiki/Using_servos_and_controlling_unused_I/O_pins.

This worked beautifully until I upgraded from 1.18.1 to 1.20RC3, now once again my heartbeat stops until macros such as auto-calibrate and home-all are completed.

JustDave

Is this the reason that my 1.18.1 M42 commands are now waiting for macros to complete before executing?

Version 1.18.2/Bug Fixes…
"M42 gcode commands were not synchronised with movement"

If so, is there some other command I can use that will execute during a macro instead of waiting for it to complete?

dc42

Why not send the M42 command before calling the macro, or at the beginning of the macro?

JustDave

Original intent was a heartbeat of 1 cycle per second to prove the processor was healthy, which worked great in 1.18.1. Now the M42 has to wait for a long move to complete, which can take up to 20 seconds at first layer speeds. I would rather not wait that long to cut power to a non-responsive Duet board.

What about a M400 parameter (S-1?) that forces "do it now" rather than "wait for current moves to finish"?

Or, back to my original request of a heartbeat on the PS_ON pin…

@dc42:

If I decide to add firmware support for a heartbeat on PS_ON, what frequency would you want, and what duty cycle?

JustDave

I figured out a way to get a perfect heartbeat…

M307 H3 A-1 C-1 D-1 ; Disable heater 3 to make it available for Watchdog timer
M42 P3 S0.50 F2 ; Switch I/O pin 8 (HEATER3) on expansion header at 50% PWM at 2 Hz

Works great; inspired by this posting: https://www.duet3d.com/forum/thread.php?id=1866#p17119

Gotta love this forum.

dc42

Ok, but bear in mind that the PWM on that pin is generated by a hardware peripheral inside the MCU, so it's presence doesn't mean that the firmware is still running correctly.

JustDave

At this point, I’ll take what I can get. I appreciate the feedback. Any way I can rescind the “answer” token?

Edit: marked as unsolved