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Temperature detector design

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May 5, 2011
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As a school project i am supposed to desing a circuit that has three leds, one will light when it is lower than 20*c, one between 20 and 30 , and one when higher than 30*c. I can use the device AD22100. it has an output voltage equation like :
VOUT = (V+ / 5 V) × [1.375 V +(22.5 mV/°C) × TA]
where v+ is typically 5v and ta is the temperature.
calculations show that 20*c outputs 1.8v and 30*c outputs 2.1v. I can not find a way to detect this voltage intervals.
Do you have any ideas on how to achieve this?. We are allowed to use any components- diodes, zener diodes, ttl gates, mosfets etc.

Strange. The datasheet states the device can only drive small loads, 1 to 2 mA.

When output reaches, say 1.7 V, this can drive a red led.
But without a resistor in series it will hold the output at 1.7 V. Did the professor say you can use resistors?

Are all led's allowed to be lit at the same time?
If so then you might find another led that will light at 2.1 V. Different voltage ranges apply to different color led's.

If you're very meticulous, you can devise a resistor network that will divide down a target voltage so that it just starts to bias an led. You adjust the divider to the led turn-on voltage.


Oh, you ARE allowed to use components.

The easy way is to use an op amp as a voltage level detector. You may need two or 3 of them.
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