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Resistance Touch Sensor

February 26, 2012

What is resistance touch sensor circuit?

It is a simple circuit designed to turn on or off a device on output or too put IC in High or Low state.

How it works?

It works by sensing (when you touch anode and cathode) and on that basis it activates or deactivates a device that is connected to the output in circuit. In my example it works like this.

When a user touches the “resistance touch pad” that is in one end connected to positive (9v) and another end is connected to transistors(BC547B) Base, the flow of “electricity” activates transisotor which in this case starts to conduct and activates LED’s that are connected to transistors emitter via resistor.

For better understanding it would be easier just to connect 1 LED via 470 Ohm resistor but i like to complicate things without any reason.

I connected 5 Blue LED’s: First three are in parallel to each other and they are in serial with two other LED’s that are in parallel. In this case i used one 10 Ohm and one 22 Ohm resistor simply because i didnt have one 33 Ohm at disposal. Such a low value of resistors is also due to the reason that Touch pad is itself a resistor and LED’s cannot get full power from battery.

It is sensitive to the area your finger covers, and because this pad is years old and coroded it is also sensitive to the force applied 😀 dont get me wrong on this one.

Since the blue LED’s can have max values about 20-30 mA and around 4V i decided to put them trough 0.03A and in total about 5.5V across all LED’s in this case devided because of wiring.

Here is clearly visible the amount that is flowing trough the touch pad and as a result brighter LED’s

Smart idea would be to use limiting resistor between touch sensor and Base of transistor which i didnt use atleast not shown in pictures.

Next post should be about either HUM sensor switch or capacitance sensor switch.

Link to video version:

Questions and comments are wellcome

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