This timer circuit uses 120 volts household mains and should only be attempted by someone that has the knowledge and skills to safely construct such a project. Otherwise personal injury and or property damage could result.
Main aquarium timer circuit board schematic.
CD4541 Timing Calculations
To change the clock timing of the CD4541 ic. R1 and C1 set the oscillator frequency and R2 should be >10K and approximately 2 times the resistance of R1.
The CD4541 in my circuit is running at approximately 36hz and is outside of the range of the specified 1kHz to 100kHz for the RC network calculation formula from the device data sheet but seems to give a calculated frequency very close to the actual operating frequency of my timer circuit.
I have the CD4541 configured as a single transition 16 stage 65536 count timer that effectively acts as a 15 stage counter 32768 count. Below I have the time delay calculation for my aquarium timer with the oscillator running at 36 hz (cycles per second).
32768 count / 36hz = 910 seconds
910 seconds / 60 seconds = 15 minutes
Oscillator frequency calculation.
Where the frequency is between 1kHz and 100kHz.
freq. = 1 / 2.3 R1 C1
Values from my circuit plugged in.
35 = 1 / 2.3 56000 .00000022
Main circuit board drawing showing components.
Aquarium Timer Parts List
| B1 - DF06 Bridge Rectifier
C1 - .22uf 25V Polyester Film Capacitor
C2 - 1000uf 35V Electrolytic Capacitor
C3 - 22uf 35V Electrolytic Capacitor
D1 - 1N914 Diode
D2 - 1N4001 Diode
F1 - 10A (1/4" x 1 1/4") Fuse
F2 - 500ma (5mm x 20mm) Fuse
IC1 - CD4541 Programmable Timer IC
IC2 - LM2941 Regulator
Q1 - 2N2222 Transistor
R1 - 56k (All resistors 1/4 watt)
R2 - 100K
R3 - 15K
R4, R5, R10 - 33K
R6 - 560R
R7 - 56K
R8 - 10K
R9 - 1K
AC Receptacle - Kobiconn 161-0715-E
Power line cord (Polarized)
PCB Mount Fuse Clips
Relay - T90S5D12-12
SW1 - Push button spst momentary switch
T1 - Radio Shack 273-1385B Transformer
(120V Primary, 12.6V Secondary)
Main circuit board. Viewing traces through top of board.
Power supply circuit board drawing showing components.
Power supply circuit board. Viewing traces through top of board.