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Circuit and PCB design by Phil Townshend c.
Project by Martin King

This project is based around a PIC micro-controller. The time is set by the rotary switch to one of 12 different settings ranging from 1 to 20 minutes. As soon as the start button is presed the timer begins counting down with the minutes remaining displayed in the dual 7-segment display. When the time is up the unit beeps for 7 seconds. After a while the unit then powers down to sleep mode until the start button is pressed to save battery power. The battery used is a 9v PP3.

The timing intervals on the switch are: 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18 and 20 minutes. These can be changes in the program.doc file in the Time variable table. If you want a pre-programmed PIC with different time intervals please specify them when you order.

Download Circuit details and PCB, (PDF - 72K).

The case was shaped from 3mm acrylic using. The acrylic was bent using a strip heater and some wooden formers. The front panel was a laminated print out produced on Microsoft Publisher.

The PCB holds all the components except the start and power switch. Care must be taken when fitting the rotary switch that it is correctly orientated and the switch connections shaped so they will fit through the PCB. Also ensure the PCB holes for the switch are drilled to at least 2mm.

The PCB needs to be secured to the front of the case. The mounting of the rotary switch holds the PCB to a certain extent, but the thread is only plastic and will not take too much strain. Try to add some other form of fixing if possible.


Rotary switch used. The connections were trimmed to fit through a 2 mm hole. you can buy types with the connections already shaped. Buzzer used a basic 6v type with around 3Khz pitch @ 80dB

Rapid part no.
R1 1K
R2-6 1K5
R7-9 1K
R10 10M
R11-17 100ohm
C1,2 100nF
C3 100u
C4 470u
C5,6 22p
C7 100u
IC1 PIC16F84
IC2 CD4511
IC3 7805
T1,2 BC183L
T3 BC212
D1-12 1N4148
D13 1N4001
LED Display Dual CC 7-seg
X1 3.2768MHz
BZ1 6v Buzzer
16 pin IC Socket
18 pin IC Socket
SW1 12way SP rotary
PB1 Push to make switch
SW2 SPST toggle switch
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