Duet3 Diag Led doesn't glow on power on when >3 proxy connect

[JayT]

Hi,

I have a duet 3 board with RRF3.4b3 flashed.
When I connect more than 3 proxy sensors ( for homing purpose), the diag led doesn't glow.
I rooted this down, by connecting one thing at a time n swapping pins.
The proxy sensor I use is PR-18-8DN (npn).
I tried giving voltage between 12-24. But somehow more than 3 create a problem.
Diag led doesn't glow and board stays in initialising state.
Can anyone suggest how to debug this further and what is causing board voltage to drop ?
I have used meanwell 24V SMPS with 6 A.
I have done similar connections earlier, and didn't face any such issue with same board n sw.

@dc42 :any suggestion to find the root cause ?
The led glows very light. What does that mean ?

[JayT]

@jayt :
Operating voltage of proxy is 24v DC.
If I provide external supply of 15V, the board works fine , diag led works as expected.

So, if we wish to run, on single mean well supply of 24v, what should we do ?

[rjenkinsgb]

@jayt
Where are you connecting the power leads from the sensors?

With the negative and signal to the Duet board input ground and signal connectors and the sensor power direct from the 24V supply, I'd expect them to work OK?

The only other thing I can think of is if they have an internal LED to 24V; that would mean they may output a voltage when off (via the LED circuit), which could upset things.

In that case, a diode in series with the sensor output to Duet input should avoid the problem; connect the cathode (band) to the sensor side, so it can still pull the input low but not feed back power.

[JayT]

@rjenkinsgb : Thank you. Fixing a diode as suggested worked well.

This thread can be marked as solved!