NAND astable timer

[madmikejt12]

i tried the circuit on breadboard and got it working, however, if the switch is pressed, then let go (i.e. door opens and closes) then it stops timing and the final output stays low (alarm doesnt go off) i thaught of using a thyristor to latch the switch, but that didnt work... so i got the thyristor circuit working on its own, and that worked.... but i cant link the output from the thyristor to the NAND gate timer... here are my 2 circuits:

Edit: i used a thyristor because i thaught it would be simple and my teacher does not want me using any more chips because it gets too complicated

 

[audioguru]

i tried the circuit on breadboard and got it working, however, if the switch is pressed, then let go (i.e. door opens and closes) then it stops timing and the final output stays low (alarm doesnt go off)

A burglar can't steal anything if the door has closed.
Your thyristor works, and a flip-flop circuit made with two gates would also work.

 

[madmikejt12]

A burglar can't steal anything if the door has closed.

good point

Your thyristor works, and a flip-flop circuit made with two gates would also work.

the thyristor circuit at the top doesnt latch, but the bottom one does

you mean 2 nand gates? that would require an extra chip