CDRIVE
Hauling 10' pipe on a Trek Shift3
OK, this is not a substitute for a proper supply but once you have one and if you still have spike issues you can try this circuit. I replaced the 7808 with a simple RC filter that should tame any spike noise on you supply. Making R1 higher, say 10Ω, will help filter things even more but its value must be made small if the relay you choose is a heavy duty model that pulls a lot of coil current. This is because the lower the resistance of the coil the more current it will demand. The more current it demands the higher the voltage drop across R1. C3 & C4 aren't critical and can be larger if you like, say 100uF or even higher.
BTW, the voltage rating of your PIR (5V to I forget) should never be used as a proper operating voltage. This is because minimums and maximums are just that. If minimum is 5V then I would not go below 6V and if 25V is maximum then I wouldn't even exceed 23V. You always want a safety margin.
Chris
BTW, the voltage rating of your PIR (5V to I forget) should never be used as a proper operating voltage. This is because minimums and maximums are just that. If minimum is 5V then I would not go below 6V and if 25V is maximum then I wouldn't even exceed 23V. You always want a safety margin.
Chris