Touch Probe

[claudef]

(11-15-2013, 06:58 AM)EdK Wrote: claudef,

There's something wrong with that drawing.

You are correct, I posted the schematic before reading my friends last e-mail stating that there is a wire missing in the circuit. I did send him you notes and he will be responding shortly.
Claude

[EdK]

(11-15-2013, 12:08 PM)claudef Wrote: You are correct, I posted the schematic before reading my friends last e-mail stating that there is a wire missing in the circuit. I did send him you notes and he will be responding shortly.
Claude

Claude,

It'll probably work fine with the added wire. It's just not considered good design practice to tie those type of outputs together. All four outputs will switch at different times due to the variations in propagation delay. It's a very small difference in time over a very short period of time so you'll likely have no problem in your application. I suggested a transistor because it would eliminate those problems and also be easier to wire in.

Ed

[claudef]

EdK, thanks for youe input.. I am not an electronic wiz so I sent the comments to my friend. Keep in mind he is French and I translated his memo to english as best I can. from what I can see, he is implementing some of your suggestions.

Claude, what he says is true, but in a same chip circuits are very similar. The peak current would last a few billionths of seconds in non-repetitive ways which is negligible. With the cmos circuit, the current consumption is 50 microamps of current at rest (LED off), this gives a period of 3 years on batteries. To use a transistor would consume 1 milliamp of current at rest which would require an ON OFF switch because the battery would last only 160 hours. But critic is good because if I add a second transistor for the first Darlington mounting, I will do a circuit with the same consumption as the cmos but simpler. I'll recalculate another circuit with two transistors. Here is the corrected cmos circuit.

[EdK]

Claude,

I'm not seeing any transistors in that updated schematic. He's added a couple of diodes but they look like they are more for over and under voltage protection.

He did make some good comments but what I said is still valid even if it is only for one billionth of a second. I would suggest using something like this part to replace the IC he is using. It'll only consume about 10uA when idle (LED off).

http://www.digikey.com/product-detail/en...-ND/770525

Please don't take this as a criticism of your friends design. It will likely work without a problem.

Ed

[claudef]

These are the parts I machined today, the probe is finished except for the spring c-bore. The ball ring is complete except the OD needs to be reduced for final adjustments. The balls are wired and ready to get pushed in their cavity, the have a .002 press fit but the center of the balls only go .010 below the top surface. The ring material is PTFE, not much sticks to this stuff, I am wondering if crazy glue or locktite would secure them. Any ideas are welcome. The soldering of the wires went relatively well, better than expected, I ground a small flat on the ball and used a soldering pencil.

[TomG]

Claude,

Unfortunately you are out of luck with finding an adhesive that sticks to PTFE. The only way to glue the stuff is to first etch the surface with hydrofluoric acid. If you made the ring out of acetal, ordinary epoxy would work well.

I would suspect the .002" interference should lock the balls in place pretty well, sans adhesive.

Tom

[MikeWi]

If the holes were widened out at the bottom, then any adhesive that would stick to the balls, should lock them into place, as the glue plug would be larger than the hole. Just an idea. :)

[EdK]

Loctite makes a primer that preps PTFE to accept super glues.

Ed

[Mayhem]

(11-15-2013, 05:42 PM)EdK Wrote: ...I'm not seeing any transistors in that updated schematic. He's added a couple of diodes but they look like they are more for over and under voltage protection...

(11-15-2013, 05:13 PM)claudef Wrote: ...But critic is good because if I add a second transistor for the first Darlington mounting, I will do a circuit with the same consumption as the cmos but simpler. I'll recalculate another circuit with two transistors. Here is the corrected cmos circuit.

I read that as saying the transistor option will come later and the schematic posted was the fixed version of the original.

It is good to see project evolve on the fly, as should be the case. After all, that is one reason for belonging to a community such as this.

[claudef]

Mayhem, yes this project is on the fly and I do accept suggestions positively, my friend the electronics guy (Yves) also reacts to positive suggestions. The nice part off "on the fly" and posting is that you can implement the suggestions as you go. It,s not always easy to do a project on the fly and post the progress, you get carried away after completing a part with success and install it before taking pictures and posting. This project however is fairly simple, the machining part that is, I an lucky to have someone for the electronics.
Claude