Design a Circuit

[YarisSi]

I've been trying to work out how to make a simple (I think) circuit but have no electronics knowledge and could find nothing on the internet. So I've just realised I might get lucky here. ;-)

The circuit needs to light LED A if the temperature falls below a specific temperature (92F/33.3C) and light LED B if it goes above 96F/35.5C.

It would need to be compact (Key Fob size) and also a test button to check the batteries are not flat.

So does anyone know where I can find out how to make such a circuit?
Thanks
Si

Sorry if you thought I meant road circuit. But that would be in General Gassing.

>>> Edited by YarisSi on Wednesday 8th December 15:38

[john_p]

How much electronics knowledge do you have?

Something like this:

www.zen22142.zen.co.uk/Circuits/Switching/coldsw.htm
doubled up, with a resistor/LED instead of a relay, and an overall test circuit that would manually switch on the transistors to check the LEDs

Although whether you'd be able to build it to key fob size, I have no idea!

>> Edited by john_p on Wednesday 8th December 15:43

[YarisSi]

None.


>> Edited by YarisSi on Wednesday 8th December 15:42

[docevi1]

is this to be in the car or hand? It'd be fairly easy to do with the right bits but if it's handheld temps will be screwy.

Whate temp are you measuring?

[simpo two]

I think you need a thermistor, which is a temperature sensitive resistor. But I have no idea what to do after that

[YarisSi]

It will be handheld.

[john_p]

YarisSi said:

None.

OK well not the end of the world .. buy a breadboard, a bag of components, some wire and a power supply, and get playing

Although it will probably be easier to just buy one if you want it key fob sized .. by the time you've gone through all the hassle.

[YarisSi]

Damn

I might see if I can find some student to make it for me.
Thanks
Si

[Pigeon]

Something along the lines of john p's reply except that with your two trigger points so close together and specified to three figures a thermistor arrangement will probably not be accurate enough. You can get temperature sensors whose output changes by a reliable 10mV per degree C. One of these, a potential divider using high-stability resistors dividing the voltage from a reference diode, and two op-amps. Piece of piss

[wedg1e]

Sounds like something for checking female fertility...
'Course you'd need different length probes, all of them labelled as 2" bigger than they really are...

[YarisSi]

wedg1e said:

Sounds like something for checking female fertility... 'Course you'd need different length probes, all of them labelled as 2" bigger than they really are...

LOL
PMSL