Here is a series of Touch Switch using only 3 transistors, this touch-based transistor switches can activate a load simply by the user touching a metal plate. It is designed to directly switch a relay to allow it to be used with large loads. As it uses only a few commonly available transistors and a 12V supply, it is ideal for hostile environments where mechanical switches would be damaged. Using a latching relay and two of these circuits, a simple two pad "touch on / touch off" arrangement can be made.
The touch pad can be most easily made by cutting a small square of PCB material and then soldering on a single wire. Alternatively, something like a penny glued to a plastic backing will do the job.
As mentioned, a latching relay can be used so that a momentary touch activates the relay and it remains active. To turn off a latching relay, power must be interrupted. So a 2nd circuit with a normal relay can be used to cut power (use the NC contacts on the 2nd circuit). Placed side by side, two touch pads form an "on" and an "off" pad.
List Component
R1_______________ 10 Meg 1/4W Resistor
R2_______________ 47K 1/4W Resistor
R3_______________ 1 120k 1/4W Resistor
R4_______________ 470 Ohm 1/4W Resistor
C1_______________15uF Electrolytic Capacitor
D1_______________ 1N4007 Silicon Rectifier Diode
Q1_______________ 2N5458 N Channel Field Effect Transistor
Q2_______________ 2N2222 NPN Transistor 2N3904
Q3_______________ 2N3906 PNP Transistor
K1_______________ Relay w/12V Coil, Contacts To Suit Application
Skema Rangkaian Touch Switch Menggunakan 3 Transistor
The touch pad can be most easily made by cutting a small square of PCB material and then soldering on a single wire. Alternatively, something like a penny glued to a plastic backing will do the job.
As mentioned, a latching relay can be used so that a momentary touch activates the relay and it remains active. To turn off a latching relay, power must be interrupted. So a 2nd circuit with a normal relay can be used to cut power (use the NC contacts on the 2nd circuit). Placed side by side, two touch pads form an "on" and an "off" pad.
List Component
R1_______________ 10 Meg 1/4W Resistor
R2_______________ 47K 1/4W Resistor
R3_______________ 1 120k 1/4W Resistor
R4_______________ 470 Ohm 1/4W Resistor
C1_______________15uF Electrolytic Capacitor
D1_______________ 1N4007 Silicon Rectifier Diode
Q1_______________ 2N5458 N Channel Field Effect Transistor
Q2_______________ 2N2222 NPN Transistor 2N3904
Q3_______________ 2N3906 PNP Transistor
K1_______________ Relay w/12V Coil, Contacts To Suit Application