In this tutorial, we are going to make two simple projects of 741 timer circuits. LM741 is an operational amplifier IC that has improved performance as compared to other op-amp ICs. It has several features that make its amplification fool-proof like over-load protection on both input and output and no latch-up.
This IC has lots of applications such as multivibrators, comparators, DC amplifiers, integrators and differentiators, summing amplifiers, and active filters. In this circuit, it is working as a comparator.
Hardware Components
The following components are required to make Timer Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Input Supply DC | 9-12V | 1 |
| 2. | Switch | – | 1 |
| 3. | Electrolytic Capacitor | 1uF | 1 |
| 4. | Resistor | 22KΩ, 1KΩ | 2, 1 |
| 7. | IC | LM741 | 1 |
| 8. | Diode | 1N4007 | 1 |
| 9. | Transistor | 2N3904 | 1 |
| 10. | Relay | 12V | 1 |
LM741 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of LM741
Timer Circuit
Working Explanation
The operating voltage of both the circuits is 9 to 12 volts DC. the difference between both the circuits is of the output, in figure 1 the LED will glow for a specific time period on pressing the push button S1 and in figure 2 the relay will be activated by when push button S1 is pressed.
The working of this circuit is simple on pressing the push button S1 it sends an input signal to the operational amplifier IC LM741, and it sends the signal to the LED. Whereas in figure #2, the output of this IC is not enough to drive a relay directly therefore a 2N3904 transistor is used. Now the amplified output is sent to the relay. A 1N4007 diode is used across the relay to save the circuit from the back EMF of the relay.
The preset time period for the activation of LED or the relay depends on the value of the 1uF capacitor. By increasing its value you can increase the preset time period, 1uf gives a time delay of approximately 30 seconds. The relay’s voltage should be the same as the input voltage.
Applications and Uses
You can connect any AC/DC electric appliance with the relay to operate it with this circuit such as lamp, fan, LED lights, etc.
