How to make a simple MOMENTARY touch switch using transitor circuit.
BC547 is a npn transistor. datasheet
Construct this schematic:
NOTE: if touch pad is small enough to connect both pads with a finger. Then you can use your finger as a touch. Otherwise you need 2 fingers.
This circuit will help you know how a touch switch works. Suppose consider Q1 circuit was not there and the touchpad was connected to Q2. Since we humans skin has some resistance, the current will flow through our body from +2v to base of Q2. Hence making the LED glow. More harder you press, less resistance of your body decreases. Hence LED will glow more brighter when you press harder.
When you connect Q1, the sensitivity of this circuit increases. Hence LED will glow more brighter with light touch on the touch pad. Try it. This is the basics of all the touch sensitive devices.
At the touch pad pin 2, if u connect a capacitor one end and other end to Q1 base. When you touch at this setup you will notice that the LED will be brighter first and then the brightness will reduce slowly to zero.
For electrolytic capacitors. + side will be connected to pin 2 of the touch pad.
Now this circuit above is tested for Relays. If you Connect a relay across the load (put current limit resistor if needed) and apply VLoad= Voltage needed to trigger the load ON. Say for my relay it was 24V. (Remember BC547 can support upto 45V. Do not forget a Reverse biase diode(flyback diode) across the relay to prevent spikes. In this configuration if you touch the touchpad, the relay will turn on. (or any Load you connected).
Have fun, Try it.
I'm not responsible for any short circuit you make. Remember do not short circuit the touchpad. BC547 will blow off.
BC547 is a npn transistor. datasheet
Construct this schematic:
This circuit will help you know how a touch switch works. Suppose consider Q1 circuit was not there and the touchpad was connected to Q2. Since we humans skin has some resistance, the current will flow through our body from +2v to base of Q2. Hence making the LED glow. More harder you press, less resistance of your body decreases. Hence LED will glow more brighter when you press harder.
When you connect Q1, the sensitivity of this circuit increases. Hence LED will glow more brighter with light touch on the touch pad. Try it. This is the basics of all the touch sensitive devices.
At the touch pad pin 2, if u connect a capacitor one end and other end to Q1 base. When you touch at this setup you will notice that the LED will be brighter first and then the brightness will reduce slowly to zero.
For electrolytic capacitors. + side will be connected to pin 2 of the touch pad.
Have fun, Try it.
I'm not responsible for any short circuit you make. Remember do not short circuit the touchpad. BC547 will blow off.
Make a simple touch switch using BC547 for LED, RELAY,BUZZER