View Full Version : Webpage on making touchprobes

04-21-2006, 08:33 AM


04-21-2006, 12:24 PM
Cool,neet idea.

04-21-2006, 12:39 PM
Way too complicated. Just fasten a probe to a small piece of black conductive foam used to protect integrated circuits from static damage. It is available in semi-rigid flexible foam types and is graphite impregnated. When it is compressed it changes resistance in a very predictable and repeatable manner. It then recovers shape nearly immediately when pressure is released. By applying a voltage across a plate on the probe to a back plate on the foam the resistance can be determined by a simple op amp comparator circuit and be adjusted for any degree of sensitivity desired. I have experimented with this and it works.

04-21-2006, 02:29 PM
I like it. Doesn't look that hard to build at all, particularly given a CNC mill to start. The idea that it follows the Renishaw patent and the demo of the text digitized are both heartening. It also strikes me as great that it triggers from side as well as vertical contact. As the site says, this is helpful when digitizing steep slopes or finding holes.



04-21-2006, 02:57 PM
I would never trust a sensor that relies on pure mechanical contacts to make or break a connection. They are far too unreliable. I am suprised he is able to get such good results. I suspect that won't last long.

I think the most accurate method would be a capacitance sensor such as is used in digital mics. That shouldn't be all that hard to make. The mechanical part would be dead simple, just one moving part. The electronics would be an oscillator controlled by the capacitance of the probe in its housing and the signal would be compared in a phase locked loop to produce an output when it changes. Another project to experiment with, later...