Electronic Heart

Description

Electronic Heart glows on and off like a human heartbeat if you use a NE555 timer wired in Astable multi-vibrator mode. Its frequency of oscillations is determined by the resistors and capacitors. Here the frequency is approximately 0.2 Hz. Each period lasts for just a little over 4 seconds.

In the Kit Electronic Heart, Capacitor (220uf) charges and discharges exponentially with time. As a result, a sawtooth waveform appears to be a ramp. Whatever be the voltage across the capacitor, it may not be utilized directly, as this will serve only to discharge/drain the capacitor. Transistor (BC548) operating in the common-emitter mode acts as a buffer, preventing loading of the capacitor(220Uf), and thereby not affecting the frequency of operation of NE555. Its emitter is connected to the four red LEDs in parallel, via a (100E) resistor. The output at pin 6 of 555 Timer is used here as the source of a sawtooth waveform.

This Electronic Board results in a gradual and smooth illumination/dimming of the LEDs. By changing the emitter resistance (10K), you can get the maximum voltage across the LED. If the resistance value is too small, the light output of the LEDs may appear to be a clipped saw tooth. If it’s too large, the LEDs will turn off for a fraction of the period. When maintained at (100E), the LEDs appear to follow the voltage smoothly.