Reed switch endstops. Anybody else using them?

A Former User · 31 Mar 2020, 08:06

@monster said in Reed switch endstops. Anybody else using them?:

Ah! It is ground and input pin!?

for swithces, yes. (inputs uses a pull up resistance so it is normally 3.3v, as such connecting the other end to 3.3v never has any effect)

monster · 31 Mar 2020, 10:16

Wooohooo! Got it!
End stops are working now!

I did reconnect as @bearer said
I did some googling/reading and find out that "M574 X1 Y1 Z1 S1 " is depricated. Added separate lines for each.
UI was replying that pins need names and then I found an example on forum with names like P"xstop" - used it
Then UI was replying that names are wrong. I was banging my head for a bit
And then found: https://duet3d.dozuki.com/Wiki/RepRapFirmware_3_overview#Section_Pin_names_for_Duet_Num_3

Here is how it looks

; Endstops
;M574 X1 Y1 Z1 S1                                ; set active low and disabled endstops
M574 X1 S1 P"!io0.in"
M574 Y1 S1 P"!io1.in"
M574 Z1 S1 P"!io2.in"

NitroFreak · 31 Mar 2020, 11:43

I found this repeatability test

https://bbs.homeshopmachinist.net/forum/general/29522-reed-switch-repeatability-test-for-cnc

which suggests a repeatability of +0.01-0.03 mm.
However, using stronger magnets absolutely does NOT improve the repeatability because the switch just triggers farther away. The magnetic field isn´t any more "defined" at the triggering distance.
I´d like to know how differing environmental influences affect the triggering distance, i could imagine EMI could drastically change that.
All in all it would be too much of a risk for my liking only to get the novel factor.

mrehorstdmd · 31 Mar 2020, 12:27

I think it would be interesting to see how it behaves when it's mounted close to a stepper that is actively stepping. You'd think the motor design would contain the field from the coils/magnets fairly well, but it probably doesn't take too much "leakage" to close a reed switch.

monster · 1 Apr 2020, 08:26

@monster said in Reed switch endstops. Anybody else using them?:

@monster said in Reed switch endstops. Anybody else using them?:

@EasyTarget said in Reed switch endstops. Anybody else using them?:
The printer which I'm working on has end switches that looks exactly same.
They are triggered by magnets. When magnet is away switch is open (infinite resistance). Magnet close - switch is closed (resistance under 1 ohm)
But how exactly did you plug them in the board?
I plugged mine to +3.3V and to io.in of IO_0, IO_1, IO_2 but somehow when I'm in "Machine specific" page Endstops table doesn't show Yes when it should...

I mean end switches on my BFB are exactly as on this topic picture:
Quite frankly I'm not sure is it reed or Hall effect, I just thought if that would be a Hall then it wouldn't be sharp step from indefinite resistance to almost zero. But anyway those switches were functioning very well under original BFB controller. And they look cool hehe and very nicely integrated into construction.

Can you imagine? Right after writing this good words about switches - one of them started to flicker (when no trigger/magnet around). In Endstops table only after attempt to park X axis it begins to flicker Yes-No. Before first homing attempt that doesn't happen.
Yesterday I spend whole evening tackling this. Using multi-meter it looks good, looks like normally opened, no sudden closings. But once used with controller and homing attempted - flickering happen (No/Yes) so homing stops 0-2 sec after start.
Wires of end switch are going very closely packed with relevant motor wires. Could there be an induction from motor wires? In the end when unplugged no such behavior noticed. And it is the only end switch with goes tightly packed with motor wires.

Danal · 1 Apr 2020, 08:48

They know. Just like dogs can smell fear... or printers can smell deadlines...

mrehorstdmd · 1 Apr 2020, 11:42

@monster The motor leads should be twisted (two twisted pairs- one for each coil) as should the endstop leads. That helps prevent inductive coupling.

dc42 · 1 Apr 2020, 12:25

@monster said in Reed switch endstops. Anybody else using them?:

Could there be an induction from motor wires?

With normally-open endstop switches, capacitive (not inductive) coupling from stepper motors wires to endstop wires can cause false triggering. That's one of the reasons that normally-closed switches are preferred. If using normally-open switches, use shielded cable for the endstops.

monster · 1 Apr 2020, 13:40

Thank you for you answers!
I just came back to report that separating the wires did the trick! All good now!
And was enjoying (like a kid I was running X and Y motors for like half an hour) how calm this motors are now! Unbelievable!!! This board worth every penny!!!

I'll have to rewire (with twisting) everything - wish I know this trick right away - it would affect choice of parts.

dc42 · 1 Apr 2020, 13:48

@monster said in Reed switch endstops. Anybody else using them?:

I'll have to rewire (with twisting) everything - wish I know this trick right away

Twisted pair wiring is good for stepper motors (one pair per phase), for thermocouple wires, and for normally-closed endstop wires. For normally-open endstops, shielded cable is better; mono audio cable is OK if you use the shield for the ground connection.

mrehorstdmd · 4 Jan 2020, 14:57

It's a good idea to twist bed and hot-end heater wires, and it doesn't hurt to twist fan leads, too. I use an electric drill with a simple tool I designed and printed.

@dc42 Good call on the capacitive coupling with NO endstops. Noted....

TP · 19 Jan 2021, 21:45

Hi All,
I have unfortunately lost the magnet for the z axis reed sensor! I am struggling to find a replacement.... does anyone have a part number or a link please?

Thanks

mrehorstdmd · 19 Jan 2021, 22:09

@TP Just about any magnet will do. If you have some earphones from an old cell phone laying around you can pull a small neodymium magnet out of one earpiece.

TP · 19 Jan 2021, 23:09

@mrehorstdmd Thank you!! i don't suppose anyone has a parts list ?

fcwilt · 19 Jan 2021, 23:22

@TP said in Reed switch endstops. Anybody else using them?:

@mrehorstdmd Thank you!! i don't suppose anyone has a parts list ?

If these guys don't have it it likely doesn't exist.

K & J Magnetics

Frederick

EasyTarget · 21 Jan 2021, 13:28

@TP The ones I used were linked above.
https://www.conrad.nl/p/standexmeder-electronics-4003004010-permanente-magneet-staaf-alnico-grenstemperatuur-max-400-c-1205896

A year and a half later and everything is still working perfectly, Repeatability is obviously excellent since the machine always holds calibration perfectly; often for weeks across dozens of homing and print cycles after a single calibration on duet powerup.