Two Astable NE555 Affects one another

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Two Astable NE555 Affects one another

Postby miyayoung » Fri Jul 28, 2017 9:15 am

I have two separate breadboards, on each breadboard I placed NE555 (here is the datesheet of ne555n) and both are configured in astable mode. Breadboard 1 is configured to 200Hz @ 50% duty cycle and Breadboard 2 is configured to 1.8Khz @ 50% duty cycle. Each breadboard is tested separately and measured with oscilloscope and the output of both is perfect. Now when the two breadboards are connected to the same battery 12v 7AH, the output of breadboard 1 changes to 1.2khz with fluctuating duty cycle while output of breadboard 2 stays at 1.8Khz and 50% DC, but if the breadboards are connected to different batteries, the output is OK, that is breadboard 1 gives 200Hz and breadboard 2 gives 1.8Khz. The problem only happens when both breadboards are connected to the same battery, and the circuit will be powered from only one source. Please, this is strange, I've not seen it before, please I need help.
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Re: Two Astable NE555 Affects one another

Postby ag » Wed Aug 02, 2017 7:33 am

Obviously, the battery connection is contaminated with 1,8Khz signals coming from breadboard 2. You need to block that signal using filter circuit, e.g. a 100nF capacitor. You should be able to see that signal on your oscilloscope.
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