Intelligent Presence Simulator

The circuit is very simple, as we have employed a microcontroller – a ‘little’ 12C508 from Microchip, which is more than adequate for such an application. It is mains powered and uses rudimentary voltage regulation by a zener diode. A relay is used to control the light(s); though this is less elegant than a triac solution, it does avoid any interference from the mains reaching the microcontroller, for example, during thunderstorms. We mustn’t forget this project needs to work very reliably during our absence, whatever happens.

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Materials

080231-PCB.pdf

080231-11.zip

Component list

Resistors
R1 = 1kOhm 500mW
R2 = 4kOhm7
R3 = 560Ohm
R4,R6 = 10kOhm
R5 = 7kOhm5
R 7 = LDR
R8 = 470kOhm to 1 MOhm
P1 = 470 kOhm potentiometer
Capacitors
C1 = 470µF 25V
C2 = 10µF 25V
C3 = 1nF5
C4 = 10nF
Semiconductors
D1,D2 = 1N4004
D3 = diode zener 4V7 400 mW
LED1 = LED, red
D4 = 1N4148
T1 = BC547
IC1 = PIC12C508, programmed, see Downloads
Miscellaneous
RE1 = relay, 10A contact
S1 = 1-pole 3-way rotary switch
F1 = fuse 100 mA
TR1 = Mains transformer 2x9 V, 1.2 -3 VA
4 PCB terminal blocks, 5 mm lead pitch
5 solder pins
PCB, ref. 080231-I from www.thepcbshop.com