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I have two 555 timer chips. The 1st is used to create a transition every .1 seconds while the 2nd is used in a monostable configuration to debounce a button. When using my DLA to look at the output of the debouncing 555 timer, I am seeing small spikes in the output that correspond exactly with the frequency of the output of the other oscillating 555 timer. I have attached my schematic showing my interconnections. Note the schematic shows connections to a terminal block. However, in my breadboarded version I have a 100K Ohm resistor tied to positions 7 and 8 of the block and a button tied to 5 and 6.

It is also the case that the LED's along with current limiting resistors or NOT in my current circuit when I am doing this recording.

I have also attached a screen shot of the trace from my DLA.

Schematic

DLA Trace

The 555 timer I am using is the SA555 chip.

Any thoughts on how to prevent this would be greatly appreciated.

With Decoupling capacitors of .1uF and .01uF on the power rail of the 2nd 555 timer

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  • \$\begingroup\$ This is just a canned comment to let you know that what you're trying to build from discrete analog components (possibly incorporating Opamps and/or NE555) is a digital control problem and thus can easily and with lower parts count be solved with a microcontroller with really minimal firmware to write. \$\endgroup\$ Dec 16 '19 at 21:46
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    \$\begingroup\$ I don't see any decoupling caps on the supply rails of the ICs, you might start there if they really don't exist. \$\endgroup\$
    – John D
    Dec 16 '19 at 21:48
  • \$\begingroup\$ Thanks @JohnD I will give that a try and report back. \$\endgroup\$ Dec 16 '19 at 21:58
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    \$\begingroup\$ @MarcusMüller Yes, am aware of that. I am working on an educational project that specifically uses the 555 timer chip as part of the experience. :-) \$\endgroup\$ Dec 16 '19 at 21:58
  • \$\begingroup\$ @KevinMcQuown that's an excellent reason :) \$\endgroup\$ Dec 16 '19 at 21:59
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You have no decoupling on your components. IC's have recommended decoupling capacitors on VCC/ power inputs for that very reason - to decouple the IC from extraneous noise in your circuit.

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Needed decoupling capacitors. Once I added a .1uF and .01uF capacitor to the vcc input of the 2nd 555 timer, the high state smoothed out considerably.

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