# Simple long duration timer circuit

Simple long duration timer circuit using OP-AMP ICs
If you need to build the RC timer circuit that long time delay we need to use too many resistors and capacitors. This may have caused the error is quite large. From the change to device degradation and leakage.

This circuit allows the RC time constant of the time up to 100 times ever. In principle, reducing the current that uses charge to the capacitor so will cause the voltage to rise up slowly.

## How op-amp long timer works

In the circuit diagram, when press button S1, C1 will be discharged out. It causes the IC1’s output that connected by follows voltage is also 0 volts. At the inverting input of IC2 will have the voltage lower than other input, cause the output of IC2 is higher positive.

The voltage across R4 while about 120 mV. Thus the capacitor-C1 so get charging through from R2 by the current about 120 nA, which approximately 100 times that of Connection resistors R2 and C1 to the positive voltage. Then C1 is charged fully and then a constant voltage of 120 mV, then it will stop charging.

Consider the below of R4 to return to the output of IC1. And while the voltage across C1 increases, It makes the output voltage and R2’s voltage increase as well. Until the output of IC1 higher than 7.5V.

According to the set to the non-inverting input of IC2 by R6 and R7, it makes the output of IC2 is “0”. The feedback little by R8 to eliminate noise caused by the output of IC1, to be extended to the IC2, giving effect to the output it took to motivate other circuits anymore.

The period of the circuit is given by the equation.

From this equation, it is evident that much hassle. In a moment, we can roughly equal to 100 multiplied by the C1. The C1 is measured in micro-farads, if C1 is the first micro-farads, it is time to 100 seconds. Multipliers can be changed by changing the R2 is adjustable. Or R61 and R7 to the Tunable value of 10 kilohms.

Note:
R4: 100 ohms ¼ W resistors
R3: 3.3K ¼ W resistors
C2: 1nF or 0.001uF 50V ceramic capacitor
IC1: CA3130, OP-AMP IC

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