Accurate 50Hz Oscillator Circuit Using 555 And 7490
This circuit is a getting a 50Hz pulse. It comprises a 555 timer and two 7490 divide-by-ten counter chips 7490.
| PARTS LIST | |
| R1 | 2.2kΩ |
| R2 | 142kΩ (120kΩ + 22kΩ) |
| R3 | 5kΩ PRESET |
| C1 | 0.001µF (102) |
| IC1 | NE555 |
| IC2 | 7490 (SN74LS90N) |
| IC3 | 7490 (SN74LS90N) |
| IC4 | 7805 Regulator |
The 555 generates a frequency of almost 5KHz which can be adjusted by VR1. This pulse fed to one divide-by-ten counter IC2 (7490) which gives an output of 500Hz (500KHz/10=500Hz). This frequency of 500Hz is again fed to the next counter IC3 to get 50Hz pulse (5ooHz/10=50Hz).
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To get accurate 50Hz pulse, the 5k preset has to be set.
The circuit works on a regulated supply of 5V.
If you reducing R2 (like 120kΩ), this circuit uses as 60Hz oscillator.
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