Hi,
a frequetly asked question. Thus there are discussions/solutions in the forum already.
some questions about o your circuit.
* an optocouper is for isoation. Do you need isolation at all?
* a relay provides isolation. A gain: do you need isolation? The relay connection seems that you don´t need isolation at all.
* do 5V and 12V reference to the same ground?
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from what I see .. you don´t need isolation. Thus you dont need a relay. A simple logic level MOSFET (plus a freewheeling diode) will do the job.
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Part selection:
Just go the the internet site of the distributor of your choice and use the according selection tool. Then input your design parameters. We don´t know them.
You will find many parts fitting to your requirements. You are free to choose...
Klaus