Duex4 and Servos / BL-Touch
ChrisParish last edited by
I have a Duet 0.8.5 with the Duex4 expansion board and I am wanting to connect a BL-Touch. From what I can see the usual way is to use one of the heater channels as a servo output by connecting to the expansion connector on the Duet. However, that connector is in use in order to connect the Duex4. A quick look at the schematics shows that the heater outputs on the Duex4 switch between VIN and GND which would let all the magic smoke out of the BL-Touch.
So my question is this - Which of the following possible solutions would work best:
Intercept the signal in the ribbon connector, leaving the input on the Duex4 floating
Solder the PWM signal cable for the Bl Touch to the relevant pin on the bottom on the Duex4
Add a level shifter to the appropriate H- pin
Non of the above (Suggest an alternative please)
Alternatively, is it possible to output a PWM signal on the PC4_PWML1 pin on the Duex4 expansion port (physical pin 10, Logical pin 69)? If so I could add some additional electronics (arduino, perhaps) to convert this signal into a valid servo signal.
The DueX4 expansion pins that are available are listed at https://duet3d.com/wiki/Using_servos_and_controlling_unused_I/O_pins. What I can't remember is which ones (if any) are servo-capable. Any that are could drive the bltouch directly because it seems to be happy with a 3.3V signal.
Other than that, all of your suggestions sound suitable. For a level shifter, a small signal diode and pullup resistor to +5V would probably be sufficient.