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Why is my 555 timer keyboard starting with noise? Answered

Hi!!! :/) I have made a 555 timer keyboard using a tactile button series with resistors, but rather than staying silent until I press a button, it makes noise as soon as I start it. All the buttons function properly, raising the note in intervals but it starts with sound. I have thoroughly searched my button/resistor series for accidental bridges between joints but have found none. This is my first "real" soldering/perfboard projects, so mistakes could have been made! Could there be any other reason for this noise? I cannot find somewhere else where the circuit may be completing. I have included the schematic I am using.

Any help would be appreciated ]:>) 
Thanks!!!!

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0
iceng
iceng

Best Answer 3 years ago

To calm a 555 add a 0.01 to 0.1 uF capacitor to pin_5 and ground..

Another concern, is the wiring to the buttons which can capture radio waves and cause the sensitive flip-flops in the IC to trip if there is no calming cap...

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ToggleSwitch
ToggleSwitch

Answer 3 years ago

I'll add that capacitor! Thanks!!!

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rickharris
rickharris

3 years ago

The output of the 555 is dependent on the charging and discharging of the capacitor C1. and resistor R5

When you turn on the capacitor has to go through a charge cycle to set the 555 times up ready for use. I expect this is where the noise comes from.

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ToggleSwitch
ToggleSwitch

Answer 3 years ago

I will try letting the capacitor completely charge/discharge.

Thanks so much!!!!