Touch Probe

bandamnits

bandamnits
I'm trying to wire a Drewtronics S5000LED Probe but i have a few questions. I've followed the wiring diagram from another thread installing a 56k ohm resistor but the LED isn't coming on and when i engage the probe nothing happens. I'm using a 24v power supply.



Also i am going to install a touch off plate I purchased from ebay and want to make sure that is wired correclty also. I plan on running the 24v though the switch into the Masso directly similar to how i have my homing switches.

Thanks in advance for any help.

Andy
 

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keymont

keymont
Hi Andy,

The docs for that probe say that the red wire should go to the Masso input and the black wire to ground. That means, that you should have the 5.6k resistor going from +24v to the same input that the red probe wire goes to, which will hold that line at 24V.


Also, I think you want a 5.6k resistor, not 56k.

Internally, there s another resistor and the LED, but they are normally shorted out by the 3 internal switches, which also keeps the Masso input held low. When one of those switches opens up, current flows through the internal resistor, to the LED, causing it to light up, and allowing the Masso input to go high.

It s actually a clever little circuit.

mike
 

breezy

Arie
Staff member
@bandamnits

Hope "installing a 56k ohm resistor" is a typo.

The way the Drewtronics works is that internal switches short out the LED & it's limiting resistor (short the power supply leads) and pulls the MASSO input low. Upon contact the switches open, lighting the LED and send the MASSO input high. Therefore the series resistor needs to be about 5.6K to allow enough current to flow to light the LED.

With the touch off plate, as long there is no chance of shorting out the power supply you should be OK wiring in the same manner as the homing switches.

Regards,

Arie.
 

bandamnits

bandamnits
Quote from keymont on January 24, 2020, 1:39 am

Hi Andy,

The docs for that probe say that the red wire should go to the Masso input and the black wire to ground. That means, that you should have the 5.6k resistor going from +24v to the same input that the red probe wire goes to, which will hold that line at 24V.


Also, I think you want a 5.6k resistor, not 56k.

Internally, there s another resistor and the LED, but they are normally shorted out by the 3 internal switches, which also keeps the Masso input held low. When one of those switches opens up, current flows through the internal resistor, to the LED, causing it to light up, and allowing the Masso input to go high.

It s actually a clever little circuit.

mike

Thank you for the clarification. I wanted to clarify where the resistor goes + or - because i've seen conflicting schematics.
 

bandamnits

bandamnits
Quote from Breezy on January 24, 2020, 2:30 am

@bandamnits

Hope "installing a 56k ohm resistor" is a typo.

The way the Drewtronics works is that internal switches short out the LED & it's limiting resistor (short the power supply leads) and pulls the MASSO input low. Upon contact the switches open, lighting the LED and send the MASSO input high. Therefore the series resistor needs to be about 5.6K to allow enough current to flow to light the LED.

With the touch off plate, as long there is no chance of shorting out the power supply you should be OK wiring in the same manner as the homing switches.

Regards,

Arie.

Yes i meant 5.6k not 56k. Just wondering what would cause the touch off plate to short? The machine is metal so it could become a ground.
 

breezy

Arie
Staff member
Andy,

Depending on the type of touch off plate that you are using, switch or contact.
  • Switch - two wire switch - one to MASSO input, other to PS
  • Contact - one wire - connected to both PS +ve & MASSO input, tool is grounded - connected to PS -ve.

Contact type requires a 5.6K resistor between touch plate and PS.

Regards,

Arie.
 

breezy

Arie
Staff member
OK, that needs to be installed the same as the Drewtronics, because of the LED in the "knife" circuit. In this I'm assuming that the knife switch operates before the over travel switch. The over travel switch is surplus to requirements for touch plate operations.

Regards,

Arie.
 

testyourdesign

testyourdesign
@breezy

It turns out that @bandamnits was not able to make the Drewtronics probe work with the resistor on the +ve wire as you described. He ended up removing the LED to make it work. I had to do the same thing when I installed my Probe. Did you actually wire your Drewtronics probe that way on your machine?

Cheers, Stephen Brown
 

breezy

Arie
Staff member
Stephen,

I'll check next Monday when I visit the shed again. I have it working with the LED in, no mods to the Drewtronics. But I've added extra wiring to prevent the spindle starting when the Drewtronics is plugged in.

Regards,

Arie.

PS. Searched the forum and found my topic Spindle start up with Drewtronics connected. And here is how I wired the Drewtronics.

Drewtronics-probe.jpg
 

breezy

Arie
Staff member
@bandamnits, @testyourdesign

Andy, Stephen,

I'm curious as to how you have the Drewtronics wired.

Fig 1 in the attached is the correct way and works, Fig 2 will not work.

Although they look the similar, the MASSO input in Fig 2 will swing from 12v to 4v when S2 opens and it is this 4 volts that keeps the input high and NO change is seen by the MASSO. Physically disconnecting the LED will cause the input to travel to 0 volts and hence trigger a change.

In Fig 1 the MASSO input is held low (0 volts) until switch S1 opens then it raises to 8 volts triggering a change.

Regards,

Arie.
 

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bandamnits

bandamnits
Hey Arie,

I have mine wired like "Fig 2" but looking at your diagram i now see the problem I was having.



Thanks for the help,

Andy
 

breezy

Arie
Staff member
Andy,

If you haven't wired up your touch plate, wire it to fig 1 and it should work correctly.

Regards,

Arie.
 
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