Digital thermometer circuit based on CA3162 CA3162 and LM35

Posted on Feb 5, 2014

A simple digital thermometer circuit with out a micro controller and having a seven segment LED read out is shown here. The circuit is based on three ICs: CA3162, CA3161 and LM35. CA3162 is a monolithic analogue to digital (A/D) converter that has BCD output. The A/D converter inside the IC is a dual slope type with differential inputs. The IC has

Digital thermometer circuit based on CA3162 CA3162 and LM35
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an internal timing circuitry and hold function. When the hold function is enables, the output IC latches itself to the present state. CA3161 is a monolithic BCD to seven segment converter IC. It can directly drive a seven segment display and there is no need for current limiting resistors. LM35 is a three terminal precision temperature sensor IC from National semiconductors. The output of LM35 is highly linear and has a scale factor of 10mV/C. The IC consumes only 60uA as standby current and is calibrated directly in degreeCelsius. IC LM35 is used for sensing the temperatures. A voltage proportional to the temperature will be available at pin 2 of the LM35 and this voltage is coupled to the high input pin (pin11) of the CA3162. CA3162 does the job of converting this analogue voltage in to a BCD format. POT R1 connected at pin 13 of the CA3162 is used for gain adjustment while POT R2 can be used for ZERO adjustment. Capacitor C2 is the integrating capacitor of the A/D converter circuitry inside the IC. The working of the CA3162 is as follows, the voltage applied to the input pin (pin11) is converted into a current (using the built in V/I converter circuit) that charges the integrating capacitor C2 for a preset amount of them. Then the integrating is disconnected from the V/I converter circuit and a reference constant current source is connected to the integrating capacitor. The time taken for the charge to restore to its...

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