I've remixed the laser filament sensor housing and added a placeholder for a micro switch.
The laser sensor works great for most filament types, but not so well for some others. I barely have issues with extruder grinding, so my main concern was running out of filament and this is where the switch does a great job.
A microswitch is easily added to the laser sensor pcb and the laser sensor can be turned off for filaments that the laser doesn't detect that reliably while the switch will still detect when running out of filament.
I've also increased the distance from the filament centre to the PCB to 9mm and that seems to help with the measurement accuracy.
To turn off the laser sensor and only rely on the switch use the S0 parameter with the M591 command. Don't forget to set P6 to enable the switch (P5 is for the laser filament sensor without additional switch).

Note that this is for V1.7 of the PCB and there are minor changes to V2.0

You can find the design here https://www.thingiverse.com/thing:4306968

@dc42 hmm, wouldn't have thought that to be an issue. I've printed lots of CF infused parts over the years and wear and tear so far has been very minimal (less than I anticipated).
I'll keep the roller arm in mind should I ever have to replace the switch - but this is what I had available.

@dc42 hmm, wouldn't have thought that to be an issue. I've printed lots of CF infused parts over the years and wear and tear so far has been very minimal (less than I anticipated).
I'll keep the roller arm in mind should I ever have to replace the switch - but this is what I had available.

@Phaedrux I've been wanting to do this since I got the sensor ages ago and finally got around making it.
Previously I only turned the laser sensor on occassionally when there was a chance of running out of filament, but it's hard to keep track exactly for which filaments it works reliably or not. With the switch it's such a simple no brainer.
Give it a try.

I've remixed the laser filament sensor housing and added a placeholder for a micro switch.
The laser sensor works great for most filament types, but not so well for some others. I barely have issues with extruder grinding, so my main concern was running out of filament and this is where the switch does a great job.
A microswitch is easily added to the laser sensor pcb and the laser sensor can be turned off for filaments that the laser doesn't detect that reliably while the switch will still detect when running out of filament.
I've also increased the distance from the filament centre to the PCB to 9mm and that seems to help with the measurement accuracy.
To turn off the laser sensor and only rely on the switch use the S0 parameter with the M591 command. Don't forget to set P6 to enable the switch (P5 is for the laser filament sensor without additional switch).

Note that this is for V1.7 of the PCB and there are minor changes to V2.0

You can find the design here https://www.thingiverse.com/thing:4306968

I've made a little plug with a 100k resistor that I use when only using 1 hotend and it works perfectly well (temp is reported at 24 .5 degrees).
Thanks for the adivce

I'm using different carriages with either the single E3D V6 or Chimera. Plugging a resistor into the unused plug when I'm not using the Chimera should work and I'll give it a try.

I've done this now and can confirm it works fine. Thanks for your help!

I've set my hotend cooling fan to turn on at 50 degrees for H1 or 2 for printing with the Chimera (1 fan for both hot ends)
M106 P0 S255 H1:2 T50

Now when I use a single hotend on my printer, the second thermistor is not connected the fan will be always on. I think this might be because on the display the temperature for the second hotend is reported at 2000 degrees.

The firmware must know that the second thermistor isn't connected, because t doesn't report an error (as opposed to when using both hotends and unplugging the second which is detected and flagged). Is there a way to configure the fan to ignore the H2 temperature when H2 is not connected?

Quick question, can I safely provide 5V on 5V_IN with the EXT 5V_EN jumper in place and at the same time use the internal regulator and INT 5V_EN jumper?
Looking at the schematic it's the same as plugging in the USB cable, which is said to be safe in the documentation.

Background: I've got a 24V PSU, switched via an SSD on PS_ON, that doesn't have a 5V rail and I'm supplying 5V through an external USB power supply via 5V_IN. I'm a little concerned that the external 5V cable might accidentially get pulled out during a long print job, so relying on the external for powering up the PSU and as soon as the 24V PSU is up safely getting 5V through the internal regulator would prevent that.