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Tan Timer (BC337)

2017-04-07 16:10  
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This article describes the Tan Timer (BC337). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: BC337.

Six timing positions suited to different skin types

Circuit diagram:

Tan Timer


R1_____________47K   1/4W Resistor
R2______________1M   1/4W Resistor
R3,R5_________120K   1/4W Resistors
R4____________Photo resistor (any type)

C1,C3__________10µF   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 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.


Photo-typeFeaturesExposure time
I & childrenLight-eyed, red-haired, light complexion, freckly20 to 33 minutes
IILight-eyed, fair-haired, light complexion28 to 47 minutes
IIILight or brown-eyed, fair or brown-haired, light or slightly dark complexion40 to 67 minutes
IVDark-eyed, brown-haired, dark complexion52 to 87 minutes
VDark-eyed, dark-haired, olive complexion88 to 147 minutes
VIThe darkest of all136 to 227 minutes
Note that pregnant women belong to Photo-type I


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