Sticking Home/Limit Switches - Please help

tommylight wrote:

McAdam wrote:

OR Crazy thought,

I could test with the 18V battery from my drill.... Hmmmmm.... Ghetto/Macgyver Engineering

Aaaaand lots of smoke if something goes wrong !!! Those batteries can release quite some power in an instance!
Use a resistor of anything from 1 to 10 ohm in series with the battery. More=safer.

Thanks for the tip

Todd wrote:

Would it be too much trouble for you to test the board with more than a 12v supply (closer to the 24v). (It might be that an additional external pull-up might be nessisary when using the minimal 12v supply.)

Tried it at 18.5v and the same behavior exists...

tommylight wrote:

Added some more info on the previous post.
You are right it looks to have some differences.
While we are at it, remove the 12 supply, remove the dc-dc converter, power the BOB from USB only, and check the inputs.
I will silently follow this, it is getting quite interesting chasing gremlins !

Haha, I too love chasing gremlins.

If I remove the 12v supply the inputs no longer function, this is by design with this board.

I have also tried to power the board from MB USB, External USB Power and a Powerbank... all same results. So i have put back in the dc-dc as its a cleaner install.

??? I've got nothing else.
Does the BOB supplier offer any support? A call to them could prove enlightening.

I'd be closely examining the BOB for design flaws.

Todd, Its the same board thats sold by lots of big sellers. Unfortunately, I bought it from an amazon seller (no support).

Tommy, I really appreciate your constant help!

A strange development:

I measured the pins on the MB, This is what I found:
+ Probe on MB Pin
- Probe on 0v at BOB

With the switch open the MB pin reads 2.02v
With the switch closed the pin reads 0.1v
When the pin is stuck and the switch is open pin reads 1.78v
When the pin is stuck and the switch is closed pin reads 0.1v

That slight drop from 2.02 to 1.78 is obviously enough for the MB to not recognize the change in state.

It also only gets stuck when after jogging/moving in 1 direction, move the opposite way and it "unsticks".

This all leads me to believe that when the DIR pins are pulled high, that the system dosnt have enough power...
But again, im just a Joker Engineer, not very good with electronics like this.

The 12v Supply is a 12.5A unit, currently feeding only the BOB and Motherboard (about 40w)
The 5v DC-DC buck converter has a 3A max and is based on the MP1584EN chip. Currently only powering the BOB

I have voltmeters (as per diagram) across these two, and their voltage remains constant.
However they are placed at the PSUs and not at the BOB/MB which is less than a meter away, so I dont think power loss over distance would be a factor.

Typing this again as system goofed.

I tried feeding the switches 12v (instead of 9v from bob) and measured the pins on the MB. Result = 2.3v so 0.3v higher.
Now when I jog an axis the voltage becomes 2.05v instead of the 1.78v from before. And it seems this is enough for my MB to recognise the Logic Change.

So before I go rewiring my whole machine (changing to 12v & 0v from psu, and adding a signal wire to BOB) - does anyone have any good ideas why the BOB is only giving out 9v and not 12?
I noticed there are some 1k resistors directly at the inputs... could these have anything to do with them?

andypugh wrote:

McAdam wrote:

So before I go rewiring my whole machine (changing to 12v & 0v from psu, and adding a signal wire to BOB) - does anyone have any good ideas why the BOB is only giving out 9v and not 12?

Some of it will be the forward voltage drop of the LEDs in the optos. Maybe all of it. I am not sure it is necessarily wrong.

Hmmm... didnt think of that... but theres still at least 1v missing at the MB side... (logic levels should either be 3v or 5v (or so ive read))