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Astable Oscillator Timer Circuit Diagram (1-30 Min)
Description
This circuit is founded on a straightforward asymmetric oscillator. The duration the relay remains active – and the duration it remains inactive – are independently configured. Utilizing the component values depicted in the diagram – both intervals are adjustable, spanning approximately 1 to 30 minutes.
CMOS 4093
The CMOS 4093 is a versatile integrated circuit functioning as a simple inverter. It’s a four-stage CMOS inverter, commonly utilized in digital logic circuits for signal inversion. Its inherent low power consumption and high switching speeds make it ideal for a wide range of applications, including oscillators, logic gates, and other digital circuits. The integrated nature of the 4093 simplifies circuit design and reduces component count, contributing to improved performance and reliability.
Schematic Diagram
Setting The Timer
The oscillation frequency of the Astable Oscillator is determined by the value of C1 and the rate at which it charges and discharges through the resistor network. The length of time the relay remains activated is controlled by R2. And the length of the time it remains inactive is controlled by R3.
Due to manufacturing variations – the precise length of the time intervals accessible depends on the characteristics of the actual components you’ve employed. R1 & R4 establish the minimum period lengths at approximately 1-minute – while R2 & R3 set the maximum periods at around 30-minutes. You are free to select component values that align with your specific needs. If your time intervals don’t necessitate high precision – and a degree of approximation is acceptable – you can omit the potentiometers altogether – and rely solely on R1 & R4 to set the times.
IMPORTANT
Do not utilize the “on-board” relay to switch mains voltage. The board’s layout lacks sufficient isolation between the relay contacts and the low-voltage components. If you require to switch mains voltage – mount a suitably rated relay in a safe location – Away From The Board. I’ve used a SPCO/SPDT relay – but you can use a multi-pole relay if it suits your application.
Alternative Capacitor
A standard electrolytic capacitor is polarized. If the charge on its plates is reversed – DC current will flow through the capacitor. If the current is sufficiently high – the capacitor will heat up and explode.
When the oscillator is operational – the polarity of the charge on C1 consistently reverses. Consequently – C1 must be non-polarized. However – you can mimic a non-polarized 470uF capacitor by connecting two 1000uF polarized capacitors in reverse polarity – as depicted. The principles and reasoning behind this configuration are detailed in the Comprehensive Circuit Description. Because non-polarized capacitors aren’t widely available – the prototype was constructed utilizing two polarized capacitors.
Veroboard Layout
The timer is intended for a 12-volt power supply. However – it will operate within a range of 5 to 15-volts. All you need to do is select a relay suitable for your supply voltage. The CMOS gates are being employed as simple inverters. Therefore – although I’ve incorporated a CMOS 4093 in the circuit diagram – a CMOS 4001 or CMOS 4011 will perform just as effectively.
Part list
