for my project im building a circuit on a breadbaord which im trying to make "warn the driver when its cold outside" im doing this by building a 555 astable with an LED as the output, a 555 monostable to trigger the astable to stay "high" for a certain amount of time then go "low".
my question is how do i link a thermistor to the monostable to the astable?
o can build then seperatly but i dont know how to link them!!

 

Don't understand why you want both an astable and a monostable. Do you want the circuit to stop blinking after a certain period of time?

A comparator can detect the thermistor voltage and inhibit the 555 operation (keep Reset pin low) until the temperature drops below your desired warning temperature.

 

thanks for the reply and yes i do want the LED to stop blinking after a while or else it will just get ridiculously annoying..
ive built the monostable and the astable but i dont know how to connect them together!
(im still nooby with electonics)

 

Below is the basic hookup for the comparator and two 555 circuits. I didn't show the rest of the 555 circuit or the power connections since I figure you can take care of that. I can help you with some of the calculations if you like.

Make sense?

 

What exactly is an "a-level" project?
Is it a Freshman thing or a senior thing? I hope it's not Grad school.

 

is there any way of doing this without a comparator?
an a-level is 2 years of college in the UK just before university..
thanks for your replies!

 

A very small uP would do this. If you use something easy to program like a little Picaxe 08M2 and a DS18B20 sensor, you wouldn't need any other parts and could whip it together in no time..

FWIW-You can use an op amp instead of the comparator. Either way, make sure the current through the T-mister is low enough to keep it from self heating.

I can't think of any analog sensor that does not require some sort of signal conditioning.

 

is there any way of doing this without a comparator?
................

Why don't you want a comparator?

 

I wish they had Electronics as a subject when I did my A-Levels. I would have aced it.
Instead I had to take two Maths, Physics and Chemistry.