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Inductive Touch - Circuit and Name?

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Would you recommend this system over the 555 timer circuit, specifically for my application, where the touchpad is the entire aluminium brick.
 
I also found this thread, which talks about another technique:
https://www.electro-tech-online.com/threads/touch-activated-switches.102791/


Ok, I can tell you a little about this circuit. I've have been bench testing it for a couple weeks now.

Currently, I have about 100ft of 3 conductor microphone wire I'm just using 2 of the wires. One wire out for the exciter and the other is a return for the receiver.

At the end of the 100ft wire 5ft apart from one another are ( 2 ) 1/2" dia bolts about 1" long screwed into a steel plate 2"x1"x1/2" (Width x Length x Depth). The end of the bolts hex is a surface of about 3/4" of an inch acting as my Touch Surface Area.

It's been running Night and Day the only problems so far; are people stepping on the wires in a bunch on the floor, falsely activating it.

Edit: The reason for choosing this one was to create multiple Touch Points in the room. Depending on your situation I would think it should work with your brick aluminum.

Edit:Edit: I will be running this wire into a ceiling with about 8 Florescent Lights along with other wire I have ran as well. That will be the true test. My office has about 4 Florescent Lights
 
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Just to make sure I understand this, this generates a signal which runs through a long length of wire. Then there is another wire that runs close by for the receiver? When a user touches the receiver and the signal wire, the receiver picks up part of the signal from the signal wire?

I may well have got that wrong, but if I havent, then I cant see how I can make that work for my application, because I only have one large aluminium block, not a receiver and a signal wire.
 
Alternatively, could I attach the signal wire on one end of my brick, and the sensor on the other side of the brick. Then when I touch it it might alter the signal picked up by the receiver?

Urgh this is too complicated
 
Alternatively, could I attach the signal wire on one end of my brick, and the sensor on the other side of the brick. Then when I touch it it might alter the signal picked up by the receiver?

Urgh this is too complicated

hi spadez,
It might be easier if you tell us what the application requirement is, we may be able suggest other ways of getting the job done.;)
 
Hi,

Yes that makes sense. It is basically to control a lamp. Its going to be like this touch lamp:

YouTube - Bulb Shaped Touch Sensitive Lamp

The touch sensing switch will be linked to a PIC which will control things, like the PWM to control the brightness based on the number of times the lamp has been touched.
 
Alternatively, could I attach the signal wire on one end of my brick, and the sensor on the other side of the brick. Then when I touch it it might alter the signal picked up by the receiver?

Urgh this is too complicated

There are 3 parts to this circuit. First you create the (1) Exciter signal, that is what I'm sending out to the benches.

Then what I did is build the (2) sensor part of the circuit, that is the part with the wire that should be attached to your brick.

Then I have the wire coming back to my control room where the last (3) part is the receiver and it's circuit will then affect the Mosfet which can turn on a light, but it would only be Momentary contact this is not a latching circuit. But someone here may be able to take that part of the circuit and put it into a pic and could be used to increase or decrease brightness?

Edit: Now if you plan more than one Touch Point.

Then you would need to create part (2) each time and wire it in Parallel with the exciter signal and back to the receiver part (3) which is also in parallel.
 
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Hi Killivolt, thank you for your reply. I understand that I attach the sensor to the brick, to "pick up" when I touch it, and I understand the receiver wire would be connected to my pic (possibly more complicated than that) so my PIC knows the situation, but im still a bit confused about the exciter signal. What would I do with the exciter signal in my circuit, would I attach it to the other side of the brick?
 
Hi Killivolt, thank you for your reply. I understand that I attach the sensor to the brick, to "pick up" when I touch it, and I understand the receiver wire would be connected to my pic (possibly more complicated than that) so my PIC knows the situation, but im still a bit confused about the exciter signal. What would I do with the exciter signal in my circuit, would I attach it to the other side of the brick?

No, it is there to create the needed sensitivity for the sensor circuit which will in turn send that response to the receiver circuit to be used.

Make sense or still fuzzy?
 
That makes a bit more sense. If I can say this outside of my head to confirm ive got it right.

Exciter Signal circuit generates a high frequency signal which is sent out to the sensor. This sensor is attached to the aluminium brick. The control wire then comes out of the sensor and (via a not yet defined circuit) connects to the PIC. Is this correct?

The sensor has the job of not only sending out the signal but also detecting a change?
 
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Isn't the light AC mains powered? Then you have an excellent AC signal from a finger that touches the metal on the lamp. That is how touch-lamps work.
 
Actually in my case I will be putting the mains into a transformer to get 12V DC which will be fed into my block.

I guess I could use a 240V AC to 12V AC, then feed 12V AC into my block. I could use the 12AC for the signal and a rectifier to convert that to 12V/5V DC for my light and PIC respectively?

Is this a good approach, or am I going haywire again? I wish I knew more about electronics! Thank you again for the help.
 
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That makes a bit more sense. If I can say this outside of my head to confirm ive got it right.

Exciter Signal circuit generates a high frequency signal which is sent out to the sensor. This sensor is attached to the aluminium brick. The control wire then comes out of the sensor and (via a not yet defined circuit) connects to the PIC. Is this correct?

The sensor has the job of not only sending out the signal but also detecting a change?

Yes, I'm in a meeting right now. Measure the resistance with your dmm. From the bottom
of the brick to the top. I'll find some scrap with a greater resistance and try it on my circuit.
 
I haven't actually make the brick yet, but I had a dig around and found some aluminium step plate. I used my somewhat unreliable multimeter to measure it and it gave a reading of 0.5 ohm. Is this a somewhat expected reading, or is it way off for a 20cm x 35 cm x 0.8 cm plate. If not, i'll do some calculations to see if I can make an estimate
 
I haven't actually make the brick yet, but I had a dig around and found some aluminium step plate. I used my somewhat unreliable multimeter to measure it and it gave a reading of 0.5 ohm

If this is similar to the one your talking about maybe. My bolts Measure about .3 and they work fine. I don't think there should be any trouble with using something a little greater in resistance.

Edit: Now you need to see how you can interphase it into your pic to produce a stepping voltage thing which; I believe is how you want it to work?

One of the Senior Forum Members can help with that; I am not an Engineer.
 
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With battery maybe. As the voltage runs down the thresholds will change but if run from a solid power source they can be very reliable.

I like a JFET for touch switches. They are very sensitive and have a high input impedance. If you bias it with a high input impedance than you will get a pulse out of the drain. Then you should buffer it so that your circuit does not load down the pulse. The buffer amp will then feed a voltage amplifier, just a good strong common emitter amplifier. From there you can have it trip a transistor switch.
 
Is 20cm x 35 cm x 0.8 cm plate 0.5 ohms. If not, i'll do some calculations to see if I can make an estimate

Ok, I went over to our surplus area and found a piece of aluminum 7ft long 2inches wide and about 1/16th inch thick. It measured about .3 ohms I couldn't find any other stuff laying around I made an adjustment to the variable resistor and the hole length of the aluminum was active as I repeatedly touched it activating my relay with each touch.

I really this could work for you.

This circuit has been reliable. I have held Cell phones next to it. Put the wire up next to my bench Florescent Lamp and turned it off and on. I have been charged and touching it several times after walking around (As I normally do at my job and returning with a loaded static finger) it still functions as before.
 
Thank you for all the information. It sounds like I might be in luck then. Ill try to create my block as quickly as I can so I can see if I can implement this circuit.
 
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