Low cost temperature indicator - one LED per degree C

The novel use of components in this electronic temperature indicator make it very simple and economical to build. It uses only three ICs, an LM335 temperature sensor, a723 (old faithfull) voltage regulator and a TL489 five stage analogue level detector. The temperature sensor ( IC1) is supplied with a constant current from the reference output of the 723 (IC2). This provides a stable zero point setting enabling accurate readings to be achieved. The circuit around the 723 is arranged to allow the output of the regulator to vary +12 V one LED per degree C between zero volts and one volt. It also acts as an amplifier with an effective gain of 20. The output is fed to the input of the analogue level detector IC3. Depending on the voltage level at its input, this IC will light one or more of the LEDs D1 .. .D5. Since the sensitivity of the sensor is 10 mV per degree centigrade (10 mV/°C), and the gain of the 723 is 20x, it follows that the TL489 requires an increase in voltage level o...