BLTouch alternative for hotbed with magnets

[dc42]

@jensus11 the humming sound is most likely caused by the PWM being reduced as the temperature nears the target. It's unlikely that you will be able to get rid of it completely (other than by using a different type of bed heater) but you may be able to shift it to a less annoying pitch using the M950 F parameter.

[jensus11]

That sounds good, what I have to change it?

M307 H0 R0.475 K0.931:0.000 D7.84 E1.35 S1.00 B0

M308 S0 P"e0temp" Y"thermistor" T100000 B3950 C7.06e-8           	; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bed" T0                                        			; create bed heater output on bedheat and map it to sensor 0
M140 H0                                                  			; map heated bed to heater 0
M143 H0 S100								             			; set temperature limit for heater 0 to 100C 

[dc42]

@jensus11 add the F Q parameter to the M950 command. Assuming it's a DC heater, try e.g. Q10, Q30, Q100.

[jensus11]

I want to test the F25 and became this message.

Fehler in Startdatei macro Zeile 69: exactly one of EFHJPSR must be given

M950 H0 C"bed" T0 F25

[droftarts]

@jensus11 Use the Q parameter for PWM frequency. See https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m950-create-heater-fan-spindle-led-strip-or-gpioservo-pin

Ian

[jensus11]

I'm using this external mosfet. If I use a different one, will the noise go away?
With Q50 the annoying sound is almost silent. Can I use it or will something break?

[dc42]

@jensus11 Q50 is fine. You will probably hear a slight buzz.

[jensus11]

@dc42
I haven't bought an inductive sensor yet. I can't find one, they're sold out everywhere.

But an idea is, of it is possible to define measuring points for the BLTouch so that I can find the position of the magnet and measure there and use this for the heightmap.

[droftarts]

@jensus11 you can define points in the mesh for the BLTouch to avoid, see the notes on G29 S4 here: https://docs.duet3d.com/User_manual/Reference/Gcodes#notes-8

Ian

[jensus11]

I have defined the mesh point in the probePoint.csv file.
But the result looks not good. I think the magnets are so strong and interfere with the BLTouch when measuring.
So on, I need an inductive sensor.

[jensus11]

I have now installed an inductive sensor. Unfortunately it doesn't work that way either.
The measurement stops above a magnet and this message appears.

Error: M280: Probe already triggered before probing move started.

What can I do?

[troydeming]

I have been using a bltouch with a magnetic bed for years with no issues. did you get it figured out?

[fcwilt]

@jensus11

In my opinion your best bet is to replace that sheet of magnets with 3M flexible magnetic self-adhesive sheet.

I've used that with all sorts of Z probes and they seem to work just fine.

I used to be a fan of BuildTak until the went with a sheet of little magnets - I've moved on from them.

Frederick