hi every body I have a signal generator thak works with 555 sometimes I see a a noise like digital FM that I think it from 50hz
Sounds like you need a power supply with better regulation!
Best regards,
Bob Masta DAQARTA v4.50 Data AcQuisition And Real-Time Analysis
Try explaining the question properly.
Graham
Bob Masta said a better power supply, which is a good guess.
There is also the "voltage reference" pin on the 555, which is pin 5. Varying the voltage there will shift the frequency of the 555 oscillator, and if it's audio frequency injected there the oscillator will be frequency modulated. Putting a bypass capacitor on pin 5 will fix that.
Of course, in order for that to be the problem, there has to be some strong AC nearby. While many 555 circuits will show that pin bypassed, I've never bypassed it 35 years of using the IC, and I've never had a problem.
Michael
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