Touch triggered contact switch

Submitted to:

Engineer Kamran Kazi

Table of content

1)Circuit Schematic

2)Working Mechanism

3)Cascading with TSOP Module

4) Project Result

5)Problems Encountered

Circuit Schematic:

Project Summary:

Touch switch comprises of two CMOS based 4027 and 4011 ICs, a quad 2 input nand gate IC and a JK FlipFlop.

Circuit Components:

R1=1MohmR2=10MohmR3=100KohmR4=2.2KohmR5=4.7KohmR6=1.2Kohm

C1=10nF 100V Polyest.C2=100pFC3=47uF 25VC4=2.2uF 25VC5=10nF 100V cer.TR1=BC550C

IC1=4011IC2=4027D1=1N1448D2=1N4148D3=LEDRL1=RELAY 12V dc

Working Mechanism:

The first part of the circuit is based on combinatorial configuration, which is than fed to a JK flipflop which provides a bistable output.

When the contact is made with the metal plates, input is fed to gate U1 which than inverts the input, a high logic converted into low is than fed to U2 gate via Diode D1, output from U2 is than high, this output is being fed to u3 will generate a final high state that will provide a clock pluse to JK FlipFlop, which will than switch into a stable state until the contact is yet made again.

When the contact is made again, the input to U1 this time will be a low logic input, and the whole process works in a reverse manner, i.e now the clock pulse input will be low from combinatorial part of the circuit.

Infrared based remote relay switching, a Viable option when cascaded:

An infrared transceiver circuit can well be cascaded with the touch triggered contact switch circuit, the transceiver will provide the means of remote switching (remote relay switching). The TSOP Module at receiver end works on modulating frequency of 38Khz, so a 555 Timer IC circuit in Astable configuration is connected at the transmitter end inorder to provide the frequency of 38Khz to Infrared LED.

555 Timer IC works as a LED Driver, since the modulation rate has to lie between 35-38Khz the astable circuit has to generate a pulse with fairly accurate frequency, as for this reason a virable resistor is connected at the receiver end to alter the frequency (since output of 555 timer IC is based on RC time constant, with variable resistor we have ‘R’ in our hands)

The frequency bandwidth can be increased with more higher variable resistor, hence it gives more option of exact tuning when using a variable resistor of high value.

Project Results:

The contact mechanism was introduced using two metal plates, with a gap which when pressured upon will reduce the distance enough to short the two ends, which resulted a successful high input to gate1.

The circuit when cascaded with the TSOP module, required a finely tuned astable pulse of 38Khz which was done via reducing the capacitance and increasing the variable resistance (to provide enough bandwidth).

Problems Encountered:

The frequency required for TSOP module to work was not accurately achieved by the use of 10k or 50k potentiometer, and capacitive value 10µF, 0.01µF, 0.001 µF.