PL-05 Type induction probe with BAT85 diode

[bubblevisor]

I tend to use the cheap PL08 or PL05 type induction probes. I normally use them with a BAT85 diode on the signal wire however I recently forgot to include this and it still seemed to work ok on my duet 2 wifi board. My question is this: is the diode necessary for the duet boards?

[dc42]

@bubblevisor the purpose of the diode is to prevent excessive voltage being applied to the Z probe IN pin if the ground wire to the probe becomes disconnected. So it isn't needed for the probe to work. However, Duet 2 revision 1.04 and later boards have protection of up to 30V on the Z probe IN pin, so with those boards the diode isn't needed at all.

[bubblevisor]

@dc42 That's very helpful David, thanks. Can you also confirm if all the duet 3 boards also have that protection?

[dc42]

@bubblevisor yes the input pins on all Duet 3 I/O connectors are protected to 30V.

The endstop inputs on Duet 2 are only safe to 8V because of the LEDs. The pins on the Duet 2 expansion connector are not protected.

[bubblevisor]

@dc42 Hmm. Does that apply if I use the 5v and GND from the expansion but signal goes to z probe in. I have a v1.04 duet 2 wifi.

[dc42]

@bubblevisor do you mean that you intend to power the probe from the 5V pin on the expansion connector? That's OK if the probe will work with just 5V supply. Most inductive sensors need more.

[bubblevisor]

@dc42 Yes that's correct. The PL05 does not work with less than 5v hence using the expansion port. Does it matter where I connect to GND? I was wondering if it made a difference using the GND on the z probe port or the pin2 GND on expansion.
Although it seems to work ok on the 5v so far, I was thinking of taking 24v directly from the power supply as the probe does indicate 6v - 30v. Are there any issues doing this? Which GND should you use in this setup?

[dc42]

@bubblevisor it doesn't matter which GND pin on the Duet you use for this purpose.