||THE STRESS METER
This Stress meter allows you access your emotional pain.If the stress is very high,it gives visual indication through LED display along with a warning beep.
It is based on the principle that the resistance of the skin varies in accordance with your emotional states. Resistance varies inverse proportional to the stress. Ie if the stress level is high the skin offers less resistance,and if relaxed resistance is high.
This property of the skin is used to measure the stress level.The touch pads of the stress meter sense the voltage variations across the touch pads and convey the same to the circuit.The circuit is very sensitive and detects even a minute voltage variation across the touch pads.
The circuit comprises signal amplifier and analogue display circuits. Voltage variation from the sensing pads are amplified by the transistor BC548(T1), which is configured as a common-emitter amplifier.The base of T1 is connected to one of the touch pads through resistor R1 and to the ground through potmeter VR1. By varying VR1, the sensitivity of T1 can be adjusted to the desired level. Diode D1 maintains proper biasing of T1 and capacitor C1 keeps the voltage from the emitter of T1 steady.
The amplified signal from transistor T1 is given to input of IC LM3915(IC1) through VR2. IC LM3915 is a monolithic IC that senses the analogue voltage levels at its pin 5 and display them through LEDs providing a logarithmic analogue display.
Here we used five LEDs connected at pins 14 through 18 of IC1.LED1 glows when input pin 5 of IC1 receives 150mV.LED5 glows when the voltage rises to 650mV and LED5 flashes and buzzer PZ1 beeps when the stress level is high.
R4 and R5 and C2 form the flashing elements.R3 maintains the LED current at around 20mA. C3 should be placed close to pin 3 for proper functioning of IC.Zenor diode ZD1 in series with resistor R6 provides regulated 5V to the circuit.
The circuit can be made on a box.
After tying the unit around your wrist slowly varies VR1 until LED1 glows (relaxed state).Adjust VR2 if the sensitivity of the IC1 is very high. The model is now ready for use