Versatile Timer Circuit for Various Applications
This circuit serves as a versatile timer, finding utility in illuminating spaces like staircases, functioning as a doorbell indicator, or controlling lamps. One of its key advantages lies in its minimal power consumption during its inactive state. Triggered by the push button (S1), IC5, a 555 timer IC, initiates the countdown. Throughout this period, the triac maintains conductivity, ensuring the lamp remains lit. The duration of the lamp’s activation is dictated by the interplay between R1 and C2 and can be adjusted to suit specific applications or individual preferences. The inclusion of R2 and C3 is essential as the 555 IC anticipates a ‘negative’ pulse at its trigger input. Upon power supply activation, C3 briefly holds the TR input of the 555 in a Low state, effectively triggering the timer IC.
Adjustments and Considerations for Optimal Performance
The specific brand and type of the 555 component should be taken into account when configuring C4 (330 nF) to ensure an adequately high power supply voltage during active states. It’s crucial to avoid employing an excessively robust version of the triac, as the circuit only drives slightly more than 5 mA into the triac’s gate. The system demonstrated proper functionality during testing with a TIC206 and the slightly larger TIC216. When selecting the push button S1, it’s essential to consider the lamp’s switching current; the switch must safely handle this current load.
To safeguard against component failure, a 15-V zener diode (D3) is connected across the power supply. R6 and R7 are incorporated to discharge C4, ensuring that no hazardous voltage remains when the circuit is unplugged. When using large values for C2, such as the 470 μF illustrated here, it’s imperative to utilize a high-quality capacitor for C4. This ensures that any potential leakage resistance will not affect the set time. Due to a subpar capacitor in our prototype, the time elapsed was significantly longer than anticipated.
