Touch activated Switches

[killivolt]

Gee. I guess I missed that. Well, CONGRATULATIONS my man! Alright

I made some major noob mistakes. but little sleep and well old age and well .... you know.

Thanks again.

 

[killivolt]

Ok, I've had this on the bench now for a week testing this circuit out. I've been allowing differing things static electricity, cell phones, no trouble.

But the one thing I've found is thermal fluctuations effect the operation. So, room temp will have to maintained for reliable operation.

How could I apply a differential to the circuit that would allow for Impedance or Capacitance changes due to room temp.

If it's just impedance maybe I can create a saw tooth pattern to the sensor increasing sensitivity.

I'm in way over my head.

Edit: Maybe that will all change when I actually install it to 60ft cable ?

 

[Roff]

I don't know why it would be temperature sensitive. Are you sure you have the PNP pin order correct?

 

[killivolt]

Yes, although I have an older 2907 in a can?

This is all they had in stock should I change it.

 

[Roff]

Yes, although I have an older 2907 in a can?

This is all they had in stock should I change it.

The can should be OK. If the emitter and collector are swapped, you will get low beta, which would cause temperature sensitivity.

 

[Space Varmint]

Well you have to do some testing. Is it on the receive side or transmit side? You could try changing one of the amplifiers to self bias which should correct for temperature.

 

[killivolt]

If the emitter and collector are swapped, you will get low beta,

This leads to an Idea.

You could try changing one of the amplifiers

Changing out parts. I might go as far as replacing the 4069's.

When I installed the bottom 4148 going to drain. I could have affected 2907 too!

I had a leaky MOSFET, because of it.

I'm changing out the 2907 first.

Edit: When I changed the MOSFET I just cut it out of circuit and soldered to the cut offs. Those may have an affect too! I'll have to push it through and solder it down.

 

[Space Varmint]

This leads to an Idea.



Changing out parts. I might go as far as replacing the 4069's.

When I installed the bottom 4148 going to drain. I could have affected 2907 too!

I had a leaky MOSFET, because of it.

I'm changing out the 2907 first.

Edit: When I changed the MOSFET I just cut it out of circuit and soldered to the cut offs. Those may have an affect too! I'll have to push it through and solder it down.

I think you hit it. Diodes are very temperature sensitive. In fact they make good thermostats.

edit*

So what that means is if it causes a transistor to switch with only slight romm temperature variations, you need to re-bias the respective transistor circuit. Apparently it is biased too close to threshold. You must compensate for it.

 

[killivolt]

I have a new question.

20khz should I worry about it? I mean what if someone has a pace maker or some kind of electronic device implanted in them.

If they touch should I be of concern about it affecting their implants?

I'm really worried about this, it came to mind when a guy from the shipping dept said jokingly.

Hey, you don't have the right to pass voltage through my body. What gives you the right?

Even though he was joking. I thought about it and he's right.

 

[Space Varmint]

I hope he don't go to any major airports. They like X-ray people with full body scanners at high intensity. A voltage passing through the body from a touch switch? This clown must not have a computer either. It's the capacitance in your finger that is amplified. An electrostatic field which is partly inductive from the liquid in your body. Nothing passing through. Possibly a mico/millivolt if he comes to work bare footed. From the sound of it, he probably does.

 

[Roff]

Some current has to flow into the body, because the PNP base current has to flow through it. The current is miniscule, and it will probably be distributed throughout the body, making the current density very low.
I personally won't guarantee that it won't interfere with a pacemaker, but I doubt it.

 

[killivolt]

Some current has to flow into the body, because the PNP base current has to flow through it. The current is miniscule, and it will probably be distributed throughout the body, making the current density very low.
I personally won't guarantee that it won't interfere with a pacemaker, but I doubt it.

I'm still working on this.

Yesterday, I received some new 4069's it completely squared the wave both top and bottom, it was really bugging me that I didn't have it.

It increased my Voltage slightly I didn't measure it.

I have my touch Circuit on the same circuit board, I know I wanted everything to remain on the same board.

But, when I increase the length to 50'ft I noticed the relay chatters if I shorten it the response is much better. I haven't tried a coax yet, but I have a spool of single conductor about 200ft left on the roll. I'll give that a try before I start messing with the location of the sensor.

 

[Space Varmint]

Try putting some capacitance from ground to both ends of the wire. I would say about .01uf but may have to play with it. Too bad your not using shielded cable. But then you would have the low impedance to deal with.

 

[Roff]

I received some new 4069's it completely squared the wave both top and bottom,

The exciter output should not be a square wave, as I think you know.

 

[killivolt]

The exciter output should not be a square wave, as I think you know.

Right, no it's not but the bugger has the same freaking voltage. I have replaced everything in the circuit.

The real reason why is before the 10k resistor I have an excellent square wave. Very good looks just like the the Diagram. Then After I have on the output side of the HEX on the rail is not a Shark tooth but it's a slopping pattern. Also, it expresses in the diagram that it should be a 9v Peak which when I measure it is 4.7v or so?

If I am to drive 50 touch sensors I will need to get that voltage up or so I think?

Edit: LIne 4

 

[Roff]

According to the simulation (I know, it's just a sim), the exciter output should be about 7V p-p.

 

[killivolt]

According to the simulation (I know, it's just a sim), the exciter output should be about 7V p-p.

Ok, I'm going to get this put on another board separating everything then.

Maybe I'm getting some sort of weird excitation distortion or something.

Edit: In my hurry to put it together I think I should have separated it ? I don't know but I know know I should have more voltage.

I will plan this on a strip board this time and cut out the sections I don't want then run the jumpers after. I hated the way I put this together anyways.

 

[Space Varmint]

Right, no it's not but the bugger has the same freaking voltage. I have replaced everything in the circuit.

The real reason why is before the 10k resistor I have an excellent square wave. Very good looks just like the the Diagram. Then After I have on the output side of the HEX on the rail is not a Shark tooth but it's a slopping pattern. Also, it expresses in the diagram that it should be a 9v Peak which when I measure it is 4.7v or so?

If I am to drive 50 touch sensors I will need to get that voltage up or so I think?

Edit: LIne 4

No, raising the voltage wouldn't be the solution. Would probaly mess up your threshold voltages.

 

[killivolt]

Ok, I got it. I didn't need to build another exciter board, I put the relay and exciter on the same board.

Then built a sensor board with a short wire. My plan is to have 8 total. Chatter is gone.