Probe Interface Board Design (resistance switching)

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23 Jan 2024 10:25 #291417 by fletch

The probe must triggered not by resistance absolute value but by increase in resistance.
So must have mcu with a voltage comparator?
 

The triggering by the probe is via an op-amp into a latch. The Wheatsone bridge allows me to 'tune out' the base resistance of the probe's contacts and wiring.

The power to the contacts is cut as resistance rises (to prevent arcing) but an MCU is too slow to do this (as was an op-amp comparator).  I use an ATtiny85 to periodically check if the contacts are still open and also to illuminate the probe's LEDs (I had two spare pins and it eliminated the need for two more transistors). The indicator LEDs on the PCB are driven by the 7404.

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23 Jan 2024 15:32 #291427 by jmelson
Wow, this looks REALLY similar to the Blum TC50 protocol. There may be some slight differences in what each bit means, but it is really similar.
Jon

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23 Jan 2024 15:46 #291428 by fletch

Wow, this looks REALLY similar to the Blum TC50 protocol. There may be some slight differences in what each bit means, but it is really similar.
Jon
 

I'm assuming you mean similar to the Renishaw wireless probe? I did consider doing the IR stuff but would need to get at least the op-amp & Wheatsone bridge on board - and if I'm doing probe-side electronics, why not just go for strain gauges or piezo?

In a rare moment of clarity I thought it best to start with baby steps - although it's more likely to happen if I make my own probe. Maybe 2024's Christmas project...

This looked interesting but I can't find an update (it's 2 years old):


 

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23 Jan 2024 15:50 - 23 Jan 2024 15:51 #291429 by fletch
I still can't seem to work out how to embed videos and my browsed still messes up the whole reply if I try to edit.

This is the video:


Edit: Ah, so just put the URL in (not YouTube's 'share' link...)
Last edit: 23 Jan 2024 15:51 by fletch.
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23 Jan 2024 16:01 #291430 by tommylight

Ah, so just put the URL in (not YouTube's 'share' link...)

Yes, for some reason the "share" link shows only as a link, but URL works fine.

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23 Jan 2024 16:31 #291436 by jmelson

Wow, this looks REALLY similar to the Blum TC50 protocol. There may be some slight differences in what each bit means, but it is really similar.
Jon
 
I'm assuming you mean similar to the Renishaw wireless probe? I did consider doing the IR stuff but would need to get at least the op-amp & Wheatsone bridge on board - and if I'm doing probe-side electronics, why not just go for strain gauges or piezo?

 

No, I have a Blum TC50 probe.  It uses IR to communicate, runs off a 9V battery, and takes fast pulses of IR to turn on/off, and then the probe output is very similar to what you describe.  But, it uses a short cone segment attached to the probe fitting, and that is pressed down on another code segment for centering.  Any deflection of the probe lifts the cone, and a rod breaks a laser beam.
This scheme removes the3-lobed pattern of sensitivity with the Renishaw balls and bars design.  Not that that pattern is anything I'd ever be aware of on my machine!
Jon

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23 Jan 2024 17:41 #291441 by fletch

No, I have a Blum TC50 probe.  It uses IR to communicate, runs off a 9V battery, and takes fast pulses of IR to turn on/off, and then the probe output is very similar to what you describe.  But, it uses a short cone segment attached to the probe fitting, and that is pressed down on another code segment for centering.  Any deflection of the probe lifts the cone, and a rod breaks a laser beam.
This scheme removes the3-lobed pattern of sensitivity with the Renishaw balls and bars design.  Not that that pattern is anything I'd ever be aware of on my machine!
Jon

 

Ah, something like this? With the bar (or something poking out the top) to break the laser beam.
 
Makes a whole lot of sense if you can keep out anything that might set it askew. I don't think my machine would notice the pattern either!
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23 Jan 2024 22:09 #291473 by jmelson

No, I have a Blum TC50 probe.  It uses IR to communicate, runs off a 9V battery, and takes fast pulses of IR to turn on/off, and then the probe output is very similar to what you describe.  But, it uses a short cone segment attached to the probe fitting, and that is pressed down on another code segment for centering.  Any deflection of the probe lifts the cone, and a rod breaks a laser beam.
This scheme removes the3-lobed pattern of sensitivity with the Renishaw balls and bars design.  Not that that pattern is anything I'd ever be aware of on my machine!
Jon

 
Ah, something like this? With the bar (or something poking out the top) to break the laser beam.
 
Makes a whole lot of sense if you can keep out anything that might set it askew. I don't think my machine would notice the pattern either!
 

Yes, that is the concept.
Jon

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31 Jan 2024 21:46 #292106 by fletch
The Mostly Printed Probe is now officially a side project...
 
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02 Feb 2024 22:26 - 02 Feb 2024 22:26 #292255 by fletch
All the stl files are now on github: github.com/Stutchbury/MostlyPrintedProbe (there is a mag-safe version in the works).

I will write a print/build guide soon, but enough distraction for now, back to the interface board!
 
Last edit: 02 Feb 2024 22:26 by fletch. Reason: typo... grrr.
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