Hi
Looking for information about a low voltage (12v from a Dewalt Battery) thyristor to trigger an alarm.
I have PIR's and tilt switches , BUT the tilt switches only have a quick pulse of 12v so need a trigger to produce a static 12v
sorry if my explanation may seem confusing not that good an explaining stuff.
The circuit comprises of a board that plays a voice message (My son wants the alarm to shout "You F'''G Bas@@D i'll break your legs) then after a pause to put on the siren and lights.
I have pir's and Tilt switches but the tilt switches that just provides a quick 12v when activated , so need some way to the alarm on a constant voltage.
any idea's ?

 

Are you sure you want a thyristor? Once triggered it doesn't switch off until you disconnect the power supply.
It really doesn't matter whether you use a 50V thyristor or a 600V thyristor, the lower voltage one is only very marginally more efficient.
Trigger current is the important parameter to check.

 

Are you sure you want a thyristor? Once triggered it doesn't switch off until you disconnect the power supply.
It really doesn't matter whether you use a 50V thyristor or a 600V thyristor, the lower voltage one is only very marginally more efficient.
Trigger current is the important parameter to check.

OK so is there something else ? Once the alarm has activated the system would be shut off to disarm the alarm anyways. so the voltage would be reset. The trigger current would be from the Dewalt battery so going through the circuit would be around 2 Amp. as its fused to that rating. Would the resistor's used with the thyristor need to be any different depending on what Thyristor voltage is used.

 

Depending on how short the pulse is, a simple latching relay circuit could work, with the benefit of no tiny connections and no sensitive delicate electronics. So the first questions are : Is the circuit to the triggers isolated? and then, how long would the tilt switch closure pulse be?
Certainly it can be done with electronics, but a simple latching relay will be a lot more flexible to interface.

 

Depending on how short the pulse is, a simple latching relay circuit could work, with the benefit of no tiny connections and no sensitive delicate electronics. So the first questions are : Is the circuit to the triggers isolated? and then, how long would the tilt switch closure pulse be?
Certainly it can be done with electronics, but a simple latching relay will be a lot more flexible to interface.

Hi the pulse depends on how long it's tilted , (it's to detect anyone climbing in the van) it is sensitive controlled so i can alter it obviously don't want it to go off in the wind, so if someone is in the van it would be on a few seconds maybe ? all triggers are wired to the board via wire. He wants all the system to be able to move from van to van.

 

A portable alarm system in a box is certainly possible. And a small relay with two Normally Open contacts will be all that is required besides the battery and whatever alarm sounding device you pick. A relay might take up to twenty MILLISECONDS to operate and seal the latch circuit. That should not be any problem.

 

I have some 9304 transistors and B772 would these be suitable ?
presume it would be like this but not sure of the resistor value.

A portable alarm system in a box is certainly possible. And a small relay with two Normally Open contacts will be all that is required besides the battery and whatever alarm sounding device you pick. A relay might take up to twenty MILLISECONDS to operate and seal the latch circuit. That should not be any problem.

Yeah but trying to find a good thyristor was the problem I tried the two in my diagram thy did not work just gave the LED i was testing a faint glow then when triggered it was brighter plus was not sure just what resistor to use, there are some diagrams BUT none I can see that actually list all the parts and are for low voltage , many for heavy duty mains. Like I said tried the one I thought would do it with just a 1k for LED and 1k for base but failed ;P
Any type of quick latching type would work just needs to give a constant 12v to the alarm via a 555 timer set for a couple of seconds delay.

 

Tilt switch used