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Multiple relay with controllers

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With R4, R9 and R13 replaced with a link it should work. As the schematic showed it, might have worked but the highest voltage you could get on U1 inputs would be half VCC (because of the voltage divider, example R4 and R1) less some extra voltage dropped by the transistor in the PC817. That might not be enough to ensure logic levels were satisfied. Personally, I would link out R4, R9 and R13 and also increase the value of R1, R2 and R10 to say 4.7K as there is no advantage in the extra current being drawn through them.

Brian.
 

Hi,

...or use a HCT595...

Klaus
 

For correct shift register operation, the clock signal has to to fulfill the maximum rise/fall time requirements of HC logic family. A standard opto coupler probably can't guarantee this, high load resistance values further slows down the edges. An ST clock buffer may be required.

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...or use a HCT595...
To save the useless series resistors?
 

Hi,

To save the useless series resistors?
No, just to minimize the count of modifications to the given schematic...

There are so many ways and so many reliable and proven circuits available ... the OP could use.

Klaus
 

Hi,

Are you aware that you didn't show the 470 resistor in your schematic?

Generally you are free to use as many resistors you like.
The only thing you have take care is to satisfy the datasheet specifications.

Klaus
 

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