Circuit diagram:
Parts:
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.)
Device purpose:
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-type | Features | Exposure time |
|---|---|---|
| I & children | Light-eyed, red-haired, light complexion, freckly | 20 to 33 minutes |
| II | Light-eyed, fair-haired, light complexion | 28 to 47 minutes |
| III | Light or brown-eyed, fair or brown-haired, light or slightly dark complexion | 40 to 67 minutes |
| IV | Dark-eyed, brown-haired, dark complexion | 52 to 87 minutes |
| V | Dark-eyed, dark-haired, olive complexion | 88 to 147 minutes |
| VI | The darkest of all | 136 to 227 minutes |
| Note that pregnant women belong to Photo-type I | ||
Notes:
- 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. Please pay attention to use only one switch at a time when the device is off, or the ICs could be damaged.
