Dome light dimmer for Cars

Hi there, back to business, previously i have post about some fun electronics on intercom and theft preventer alarm. Before i start today's post, I would like to ask all cars freaks here, what would you like your cars take part in the coolest light decorations? That would probably be a big dream for street homies with V8 under their hood or likely to say some with turbos and superchargers.

Alright that is totally out of the topic! So about doing light decoration on a car instead of a house, this is a simple circuit where you can make your car dome light fade out when you close your car door instead of just goes OFF. This unique circuit makes your dome light look cool.

 

Diagram 1

When a car door is open, the push to off switch of the door is ON and hence it charges the 22 uF capacitor fully

 

Capacitor in white area (edited with Adobe PhotoShop CS3)

The opamp is acting as a voltage follower and its output is same as the voltage across the capacitor, which is 12V when the capacitor is fully charge. Due to high voltage at the output of the IC, the transistor saturates, turning ON the bulb to full brightness.

Now when the door is closed, the door switch is push and so the switch goes OFF. When the switch is OFF, the capacitor starts discharging slowly through VR1 and the 10k resistor and the voltage across it decrease slowly.

 

White highlighted area shows the process (edited with PhotoShop CS3)

Thus at the output of IC 741 also the voltage decreases gradually, hence decreasing the base to the transistor. This produces a slowly decreasing current through the bulb and the bulb fades out and finally when the capacitor is fully discharged, the bulb goes OFF.

After building the circuit, with the push-to-off switch in ON position (not pushed in) i.e. the car door open, adjust the preset VR2 to the required initial brightness of the bulb. Then push the switch in to turn it OFF (or just close the car door) and adjust VR1 for the time to bring the bulb from full brightness to OFF.

I would suggest you set VR1 and VR2 to their maximum values. instead of using the original stock bulb in the car, u can easily replace it with white LED but adjust the maximum brightness in order not to burn the LED as it only consume 1.5V each LED.

Note: 2N3055 power transistor needs proper heat sink

But in my ride I use LED which is slightly brighter than the stock bulb. You even can put these LED's underneath the chair of your car and made it act like a neon.

That is all for today from me. hope you can join the local auto-show in your area. Signing off for today's post just from Mohamad Fairulnizam.