El cheapo sensor

Some of the AVR microprocessors have an on-die temperature sensor and bandgap reference, including the 75-cent-in-quantity 8 pin ATTiny45. By connecting up the ADC registers the right way it can measure its own supply voltage and use that to help calibrate the temperature sensor; even without more sophisticated calibration temperature measurements seem accurate to within a couple degrees C, and Vcc measurements to within a couple mV. All without any external components

Here's a '25 logging its own Vcc and temperature to a PC over a software serial link at 9600 baud. Measured Vcc on a calibrated DMM is 5.15 volts, its readings are bouncing around between about 5.14 and 5.18:

The temperature rise is me pointing a heat gun on low setting at the top of the chip from about 1.5 feet away.

You get serial output, i2c interface, and microprocessor for "free", too!

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bitrex
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'45 that is, the '25 isn't a particularly good value for only 2k of program memory

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bitrex

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