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Cross channel interferance

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New Member
I have got a problem. I designed a circuit which controls up and down movement of lights. I'm using remote digital receivers which supplies a trigger pulse of 1 seconds to a 74121 IC. It inturns provides a 0.5 second pulse (One shot). The pulse from the IC is fed to a transitor CBC182 this inturn switches a pair of relay's that have 220VAC on the NO contact. I designed three circuits that are exactly the same. All these circuits have two channels (UP and DOWN) to each channel a relay is connected. I have on each circuit a +5VDC regulater this is the only physical connection between these three circuits. These regulators are connected to a 12VDC rail. Now the problem is when I connect the 220V to the relay's and operate the one circuit the other two circuits get some sort of interferance on them and they switch the relay's without receiving a pulse from the digital receiver. So the other lights move at random. I have already grounded the unused inputs to all of the IC's. Now what can I do to stop this interferance from the 220V onto the other channels??????????? :evil:


Well-Known Member
Do you have good decoupling on your 5 volt regulators? I would connect a 10uF tantalum cap from each +5 volts to ground, and a 0.1uF cap across the power supply pins of each IC that is powered off these regulators, as well as a 0.1uF cap from the +v connection of each relay coil to the emitter of the transistor driving it. You also need a diode such as 1N4001 across each relay coil, cathode to +V, anode to the collector of the driving transistor.
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