Touch Switch

[prprog]

By experimentation I built the attach circuit for a touch switch. Over the copper trace I place a piece of conductive rubber (from the inner tube that is used on truck tires). When press the 4066 is activated. I notice that if I used a 10Meg resistor the 4066 is activated when the copper trace is touch with a finger but not with the conductive rubber place over the copper trace. So I increase the resistance to 30Meg and voila! the conductive rubber works to activate the 4066. Can you give me an explanation why it works? (I do electronics as a hobby).

Also can the 4066 be damage by using this type of circuit? My next experiment is to get the 4 switches in the 4066 to work with 4 corresponding copper/rubber sensors.

Thanks,

 

[Dean Huster]

I think you may be getting a capacitive effect there rather than a conductive effect. Have you checked (with a load and high humidity) how long the circuit remains latched? Conductive inner tube? Since when?

Dean

 

[prprog]

I think you may be getting a capacitive effect there rather than a conductive effect. Have you checked (with a load and high humidity) how long the circuit remains latched? Conductive inner tube? Since when?

Dean

The rubber on inner tube is process using carbon - so it have a conductive (small) capability.

Capacitive (uhmmm) interesting....

 

[audioguru]

Add a resistor (2.2M?) in series with the control pin so that a static electricity spark will not destroy the IC.

 

[prprog]

Add a resistor (2.2M?) in series with the control pin so that a static electricity spark will not destroy the IC.

...from pin 13 to ___?

(sorry.....an expert will know the answer...but I have no idea)

Thanks,

 

[audioguru]

...from pin 13 to ___?

Add a 2.2M resistor in series between pin 13 and the sensor.

 

[prprog]

I think you may be getting a capacitive effect there rather than a conductive effect. Have you checked (with a load and high humidity) how long the circuit remains latched? Conductive inner tube? Since when?

Dean

Capacitive...or conductive ...which one cause the 4066 to activate?
I think that it is conductive and that the copper trace /rubber act as a a voltage divider with the 30meg resistor. Am I right?

Thanks,

 

[audioguru]

The CD4066 turns on when its control pin goes high. The sensor must be at least 12M ohms for the control pin to be a valid logic high voltage.

 

[prprog]

The CD4066 turns on when its control pin goes high. The sensor must be at least 12M ohms for the control pin to be a valid logic high voltage.

How do you know that it must be at least 12M ohms?

 

[audioguru]

How do you know that it must be at least 12M ohms?

12M in series with your 30M makes a voltage that is 71% of the supply voltage. A Cmos input is considered to be high when its voltage is at least 70% of the supply voltage.

 

[Boncuk]

I think the circuit neither works conductive nor capacitive. I guess it works because of stray AC in the vicinity and touching the input AC is coupled into it.

Take the circuit to the jungle (battery operated) and it won't do a thing.

Boncuk

 

[audioguru]

Your finger's resistance is much lower than 30M and it couples the input to the positive supply voltage (assuming that the black triangle is the positive supply voltage).

EDIT: I forgot about the conductive rubber.

 

[prprog]

I think the circuit neither works conductive nor capacitive. I guess it works because of stray AC in the vicinity and touching the input AC is coupled into it.

Take the circuit to the jungle (battery operated) and it won't do a thing.

Boncuk

Hi Boncuk. I am using a patch of rubber over the copper grid. Do you still think that it is not conductive nor capacitive and if I take it to the "jungle (battery operated)... it won't do a thing" ?