Emotional Stress Meter | Make Emotional Stress Indicator Mini Project using LM3915

Stress Meter

Emotional Stress meter as the name suggests lets us access our emotional pain in an electronic format. With the help of this device, one can know the stress levels of the body. If the stress is extremely high, the stress meter gives a visual indication through a LED display alongside a warning beep. Emotional Stress meter is tiny enough to be worn around the wrist.

Stress Indicator relies on the principle that the resistance of the skin varies in accordance along with your emotional states. If the stress level is high the skin offers less resistance, and if the body is relaxed the skin resistance is high. The low resistance of the skin during high stress is because of a rise within the blood supply to the skin. This increases the permeability of the skin and hence the conductivity for current.

This property of the skin is used here to measure the strain level. The touchpads of the stress meter sense he voltage variations across the touchpads and convey the same to the circuit. The circuit is extremely sensitive and detects even a minute voltage variation across the touchpads.

Stress Meter: Circuit explanation

Emotional Stress Meter | Stress Indicator Circuit Diagram
Emotional Stress Meter | Stress Indicator Circuit Diagram

The circuit comprises a signal amplifier and analogue display sections. Voltage variations from the sensing pads are amplified by transistor BC548 (T1), which is configured as a common-emitter amplifier. the base of T1 is connected to one of the touchpads through resistor R1 and to the ground rail through pot VR1. By varying VR1, the sensitivity of T1 is adjusted to the required 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 the input of IC LM3915 (IC1) through VR2. IC LM3915 is a monolithic integrated circuit that senses analogue voltage levels at its pin 5 and displays them through LEDs providing a logarithmic analogue display. It can drive up to 10 LEDs one by one within the dot/bar mode for every increment of 125 mV within the input. Here, we’ve used only five LEDs connected at pins 14 through 18 of IC1. LED1 glows when input pin 5 of IC1 receives 150 mV. LED5 glows when the voltage rises to 650 mV and LED5 flashes and piezo buzzer PZ1 beeps when the stress level is high.

Emotional Stress Meter - Stress Indicator Display Panel

Resistors R4 and R5 and capacitor C2 form the flashing elements. Resistor R3 maintains the LED current at around 20 mA. Capacitor C3 should be placed close to pin 3 for the correct functioning of the IC. Zener diode ZD1 in series with resistor R6 provides regulated 5V to the circuit.

Stress Indicator Assembly and Usage

The circuit is assembled on a small piece of perforated board. Use transparent 3mm LEDs and a small piezo buzzer for audio-visual indications. Enclose the circuit in a small plastic case with touchpads on the backside. Two self-locking straps can be used to tie the unit around your wrist.

Emotional Stress Meter | Stress Indicator Touch Pads

After tying the unit around your wrist (with touchpads in touch with the skin), slowly vary VR1 until LED1 glows (assuming that you just are in a relaxed state). Adjust VR2 if the sensitivity of IC1 is very high. Emotional stress meter is now ready to be used.

This content is inspired by ElectronicsForU.

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