R1_____________47K 1/4W Resistor
R2______________1M 1/4W Resistor
R3,R5_________120K 1/4W Resistors
R4____________Photo resistor (any type)
C1,C3__________10΅F 25V Electrolytic Capacitors
C2____________220nF 63V Polyester Capacitor
D1,D2________1N4148 75V 150mA Diodes
IC1____________4060 14 stage ripple counter and oscillator IC
IC2____________4017 Decade counter with 10 decoded outputs IC
Q1____________BC337 45V 800mA NPN Transistor
SW1___________2 poles 6 ways Rotary Switch (see notes)
SW2___________SPST Slider Switch
BZ1___________Piezo sounder (incorporating 3KHz oscillator)
B1____________3V Battery (two 1.5V AA or AAA cells in series etc.)
This timer was deliberately designed for people wanting to get tanned but at the same time wishing to avoid an excessive exposure to sunlight.
A Rotary Switch sets the timer according to six classified Photo-types (see table).
A Photo resistor extends the preset time value according to sunlight brightness (see table).
When preset time ends, the beeper emits an intermittent signal and, to stop it, a complete switch-off of the circuit via SW2 is necessary.
I & children
Light-eyed, red-haired, light complexion, freckly
20 to 33 minutes
Light-eyed, fair-haired, light complexion
28 to 47 minutes
Light or brown-eyed, fair or brown-haired, light or slightly dark complexion
40 to 67 minutes
Dark-eyed, brown-haired, dark complexion
52 to 87 minutes
Dark-eyed, dark-haired, olive complexion
88 to 147 minutes
The darkest of all
136 to 227 minutes
Note that pregnant women belong to Photo-type I
Needing only one time set suitable for your own skin type, the rotary switch can be replaced by hard-wired links.
A DIP-Switch can be used in place of the rotary type. Pay attention to use only a switch at a time when the device is off, or the ICs could be damaged.
Source: Electronics Lab