I am looking for a circuit that would allow a laser to start an 12v alarm when the beam is cut, but i want the alarm to keep on as the beam hits again the LDR .Mainly my problem is that when the beam hits again the LDR the alarm stops. I don’t want it to stop. Or maybe use some 555chip and make it stop after 20sec or so…
Does any one know a SIMPLE(im not an electrician) circuit that I can use?
This is what im using now. **broken link removed**