Very simple circuitry
R1 4K7 1/4W Resistor
R2,R3 1K 1/4W Resistors
C1 100?F 25V Electrolytic Capacitor (See Notes)
D1 1N4002 100V 1A Diode
Q1 BC547 45V 100mA NPN Transistor
Q2 BC327 45V 800mA PNP Transistor
P1 SPST Pushbutton
RL1 Relay with SPDT 10A min. switch
Coil Voltage 12V. Coil resistance 150-600 Ohms
This device is a simple timer, allowing to keep on the headlights of your vehicle for about 1min. and 30sec., e.g. when accessing some dark place, without the necessity of coming back to switch-off the lights.
Pushing on P1 allows C1 charging to full 12V battery supply. Therefore Q1 is driven hard-on, driving in turn Q2 and its Relay load. The headlights are thus activated by means of the Relay contact wired in parallel to the vehicle's headlights switch. RL1 remains activated until C1 is almost fully discharged, i.e. when its voltage falls below about 0.7V.
The timing delay of the circuit depends by C1 and R1 values and was set to about 1min. and 30sec.
In practice, due to electrolytic capacitors wide tolerance value, this delay will vary from about 1min. and 30sec. to 1min. and 50sec.
An interesting variation is to use the inside lamp as a command source for the timer. In this way, when the door is opened C1 is charged, but it will start to discharge only when the door will be closed, substituting pushbutton operation.
To enable the circuit acting in this way, simply connect the cathode of a 1N4002 diode to R1-C1 junction and the anode to the "live" lead of the inside lamp.
This lead can be singled-out using a voltmeter, as it is the lead where a 12V voltage can be measured in respect to the vehicle frame when the lamp is on.
The Relay contact must be rated at 10A or more.
Timings obtained trying different tolerance electrolytic capacitors for C1:
100?F = 1'30" to 1'50"
47?F = 0'45" to 1'05"
220?F = 3'15" to 4'15"
Reprinted Url Of This Article:
- LED Circuits and Projects
- Automatic Room Light Circuit Schematic Presentation
- Driving dot LED (AT89C2051)
- Low Drop Linear LED Driver
- 110V Light Dimmer using TRIAC (2N3053)
- LED Audio Level (VU) Indicator and Alarm: The Dot Turns to B
- Electronic Fifteen LED Roulette (CD4514)
- USB chargeable flashlight & circuit tester with char
- Timer light switch circuit
- AC Powered-LED Flasher
- Stereo LED Power (VU) Meter(LM3915N-1)
- 6 Channel Auto Reverse Sequential Disco Running Lights (LM
- Light flasher circuit
- 7-Segment (Led) Display Driver Circuit
- 240v HV-AC HIGH POWER LED
- Automatic light dimmer circuit
- Six Zone Alarm With LED Display
- Leds Or Lamps Sequencer electronic circuit diagram
- Five-Decade Dynamic Light-Level Meter (LM114)
- Blinking LED Emulates Incandescent Bulb
- 10 led VU Meter using LM3915
- SCS-Silicon Controlled Switch
- Digitally Controlled Negative Voltage Supply (MAX837)
- An automatic headlight brightness switch circuit study
- 8 channel light chaser using 8051