An electronic timer is a circuit which is used to delay or switch various industrial and domestic appliances. There are three methods to construct a Multirange Adjustable Timer.
The first one is a monostable multivibrator. But in the case of long time delays, the components become bulky. For this drawback, this circuit is not used if a longer time delay is required.
The second method is to employ a microprocessor for extremely fine control and switching. But it is a very advanced method, as well as extremely expensive and complicated.
The final method that we are going to implement in this project is to employ an astable multivibrator cascaded with counters and a driver circuit using 555 Timer IC and CD-4017 Decade Counter.
- CD-4017 Decade Counter IC (x2)
- NE555 Timer IC
- BC547 Transistor (x5)
- IN4001 PN Diode (x10)
- 1-pole 4-Way Switch
- 6V 100Ω Double Pole Relay
- Push Switch
- 0.27uF, 0.47uF, 0.01uF Non-Polar Capacitors
- 2.7uF, 4.7uF, 27uF, 47uF, 270uF, 470uF 1000uF Polar Capacitors (All are 25V)
- LED (x3)
- 1MΩ Potentiometer
- 22KΩ Resistor (x2)
- 100KΩ Resistor
- 47KΩ Resistor (x4)
- 220Ω Resistor (x3)
- 6-0-6V Transformer
For removing messy wiring and give a clean look, I designed a PCB prototype for this project. It is also helpful for troubleshooting that runs great without any errors. To design this PCB board, I used EasyEDA as it is too easy to use. For ordering PCB for this, I prefer PCBWay.
Gerber file for Multirange Adjustable Timer Gerber.
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Working Principle of Multirange Adjustable Timer
The circuit connection for this project is shown in the diagram. Here NE555 timer IC is used as an astable multivibrator to generate clock pulses. The time period of the clock pulses can be adjusted with the 1MΩ potentiometer. The 1-pole 4-way switch is used here to control the time range.
The clock pulses are fed serially to the cascade counters formed by the two CD-4017 ICs. These two ICs are divided by 10 and divided by 9 respectively. So the output of the last CD-4017 goes high at the generation of the 90th clock pulse. The time is taken,
Td = [(0.693 (R1+2VR1+2R2)C) * 90] sec.
Where C is the effective capacitance selected by the range switch.
The delay period can be set in the following ranges.
The instantaneous state of the timer is indicated by the LEDs. If the timer is in the initial one-third stage LED 1 glows. When the timer reaches the middle one-third stage LED 1 goes off and the LED 2 glows. When the timer is in the final stage the LED 3 glows.
The first three transistors (T1, T2, T3) drive the LEDs and T4 and T5 drive the relay. When the base of T4 is low, it remains in a cut-off state and T5 is in saturation. Resulting in the relay being on. As soon as the T4 goes high it remains in a saturation state and T5 is in a cut-off state. So the relay is off.
The whole system is started with the pressing of switch 1. We use a double pole 6-volt relay to make the system auto-power. One of the poles is used to switch the desired load and the other one is to switch off the system after the delay time is over.
Characteristics of Multirange Adjustable Timer
The uses of this circuit are extensive range. The timer of this circuit can be adjusted for a time delay of 10 seconds to 100000 seconds. Also, CMOS ICs are used as counters to eliminate the requirement of a regulated power supply. So by this process, the cost of this project gets reduced.