Universal Timer with Zero Standby Current Schematic Circuit Diagram
Innovative Solar Garden Lighting Control: A Purposeful Design
This circuit was born out of the author’s desire for enhanced control over his 12 V solar-charged garden lighting system. However, its versatility extends beyond garden lighting, making it adaptable for various equipment types. Activation of pushbutton T1 initiates the relay K1, powering the entire circuit. This action energizes the 78L05, creating a stable 5 V supply for the ATtiny2313 microcontroller. The microcontroller then commands output PD3 (pin 7) to go High, activating the transistor and engaging the relay, thereby keeping the garden lights on for a predetermined duration specified in the firmware. The same button press can either turn off the lights or extend the lighting period, offering convenient control flexibility.
Extending Control with Pushbutton T1
Pushbutton T1 is intricately linked to input PD2 (pin 6) via D3. When T1 is pressed for a minimum of three seconds after the timer has initiated, a sequence is triggered. This sequence halts the timer, turns off the lights, and severs the circuit from the power supply, providing a comprehensive control solution.
Flexible On-Time Extension and Warning System
For added flexibility, the on-time period can be prolonged. A minute before the designated timing period concludes. The LED on PD6 (pin 11) illuminates as a warning signal, indicating the imminent switch-off of the connected equipment, such as garden lighting in the author’s scenario. Pressing button T1 (start/stop) once again reactivates the counter, extending the on-time further. The timer can also be manually terminated at any point by pressing T1. Modification of the timing periods is easily achievable by adjusting the values in the source code for the ATtiny2313, downloadable from [1], and subsequently recompiling the program. The presence of diode D3 plays a crucial role, preventing current from flowing into the I/O pin of the microcontroller and relay when the circuit is in its off state. Without D3, the circuit would remain perpetually switched on.
Efficient Standby Mode with Zero Current Draw
In its off-state, the circuit, including the 78L05 voltage regulator, is entirely disconnected from the supply. This meticulous design ensures a total standby current of zero, maximizing energy efficiency and ensuring minimal power consumption during periods of inactivity.
[1] www.elektor.com/090534