LM35 to ADC

The circuit described here is the digital and display section of a thermometer; the analogue circuitry and signal conditioning required to use an LM35 temperature sensor are described elsewhere in this issue (‘LM35 to ADC’). The analogue-to-digital converter used here is hidden inside a PIC16F873 microcontroller behind the RA5 port pin. It has a resolution of 10 bits (1024 steps), allowing a temperature range of 128 ?C to be divided into steps of exactly 128 ?C / 1024 = 0.125 ?C.

Resistors

R1 = 10k

R2-R13 = 220

Capacitors

C1 = 100nF

C2 = 10µF 16V radial

Semiconductors

D1-D5,D7-D11 = LED, 5mm

D6 = TwinLED (DuoLED) green/yellow

IC1 = PIC16F873-20/SP, programmed, order code 030190-41

Miscellaneous

X1 = 8MHz ceramic resonator (3 pins)

S1,S2 = BCD complement switch (APEM PT65-702)