Photodiode Circuit

[PKn]

Hi, I'm wanting to implement a photodiode relay control circuit and have browsed the internet for a circuit. Here's one that seems good, Figure 7, Simple dark activated relay circuit: http://www.sentex.ca/~mec1995/tutorial/ ... ocell.html

QUESTION: It shows a supply voltage of 12VDC. If I were to use a 5v relay, would it work with 5v supply?

Thanks

[Richard]

Should be OK - why not try the simpler circuits and see. You might have to adjust the values of the variable resistors in series with the LDRs, to get exactly the turn on/off range you want.
The 741s may not work too well on a +5v power line, but you could always power the relay from +5v, and the rest of the circuit from +12v.