Raptor1956
New Member
I have a request to provide an external/remote alarm light from a piece of equipment my company installed but the only signal source is a buzzer that goes off when the system is in an alarm state but also beeps when the automation begins to move. So, I built a simple circuit with an opto-isolator with Darlington output that power both the buzzer (25ma) and a time delay (on delay) relay (also about 25ma). I used the opto-islolator because I did not want to increase the loading of the drive circuit powering the buzzer. The on delay relay was chosen to filter out the short duration ( under 2 seconds) beeping when the automation starts so that the alarm light only goes on when the buzzer alarms for more than the time delay setting.
Now, I made the mistake of assuming that the beeping was driven by the buzzer itself and the the signal to it was not pulsing -- WRONG. So now I need to add a retriggerable delay of, say 3 or 4 seconds so that when the system goes into alarm the ouput of the retriggerable will remain on and then the on delay relay, set to somthing more than the 3-4 seconds, will operate correctly.
I could use something like the 74HC423 but since the system is powered by 24VDC I'd prefer a retriggerable able to tollerate 24VDC without having to add a 7805/7812.
So, any recommendations on component choice for the higher voltage or should I just use a 123/423 component and add the 7805/7812?
Thanks,
Brian
Now, I made the mistake of assuming that the beeping was driven by the buzzer itself and the the signal to it was not pulsing -- WRONG. So now I need to add a retriggerable delay of, say 3 or 4 seconds so that when the system goes into alarm the ouput of the retriggerable will remain on and then the on delay relay, set to somthing more than the 3-4 seconds, will operate correctly.
I could use something like the 74HC423 but since the system is powered by 24VDC I'd prefer a retriggerable able to tollerate 24VDC without having to add a 7805/7812.
So, any recommendations on component choice for the higher voltage or should I just use a 123/423 component and add the 7805/7812?
Thanks,
Brian