74HC_HCT157N

[Jay Gonzo]

Hi,
I am using this mux to design a circuit. It is a quad 2:1 mux so I am using 3 inputs and the E and S is grounded.
The 3 ouputs are connected via optocoupler to 3 relays (SPST). The problem is the when I connect the circuit the relays are continously switching on and off.
My connection is like this:
E and S = GND
IN : pin 2,5,11 and 14 from microcontroller
OUT: pin 4,7,9 and 12 connected to 3 optocoupler and to 3 relays
My problem is the relays are continously switching which I do not want.
Any ideas to this problem?
//regards,Jay

 

[Grossel]

Possible errors: Opto coupler may be disturbed by ambient light. Your circuit is wrong. Everything works but you have written bad code so it doesn't work as expected.

 

[ChrisP58]

A clearly drawn schematic of your entire circuit would help.

If you freeze all of the pins from the microcontroller, what happens to the relays?