Dome Light Dimmer For Cars

This unique circuit makes your dome light look cool. Usually when the car door is closed, the dome light just goes OFF. With this circuit, you can have our dome light fade slowly in brightness and finally go OFF. This slow dimming of the light gives a very good feeling at night. It looks very romantic!
The circuit can be explained as follows: When the car door is open, the push to off switch of the door is ON and hence it charges the 22uF capacitor fully. 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 charged. Due to a 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 pushed in and hence 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 decreases slowly. Hence at the output of IC 741 also the voltage decreases gradually, hence decreasing the base current 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 close the 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.

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Wiper Speed Control

A continuously working wiper in a car may prove to be a nuisance, especially when it is not raining heavily. By using the circuit described here one can vary sweeping rate of the wiper from once a second to once in ten seconds. The circuit comprises two timer NE555 ICs, one CD4017 decade counter, one TIP32 driver transistor, a 2N3055 power transistor (or TIP3055) and a few other discrete components. Timer IC1 is configured as a mono- stable multivibrator which produces a pulse when one presses switch S1 momentarily. This pulse acts as a clock pulse for the decade counter (IC2) which advances by one count on each successive clock pulse or the push of switch S1. Ten presets (VR1 through VR10), set for different values by trial and error, are used at the ten outputs of IC2. But since only one output of IC2 is high at a time, only one preset (at selected output) effectively comes in series with timing resistors R4 and R5 connected in the circuit of timer IC3 which functions in astable mode. As presets VR1 through VR10 are set for different values, different time periods (or frequencies) for astable multivibrator IC3 can be selected. The output of IC3 is applied to pnp driver transistor T1 (TIP32) for driving the final power transistor T2 (2N3055) which in turn drives the wiper motor at the selected sweep speed. The power supply for the wiper motor as well as the circuit is tapped from the vehicle’s battery itself. The duration of monostable multivibrator IC1 is set for a nearly one second period.

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Charge Monitor For 12 V Circuit Diagram

A battery is a vital element of any battery-backed system. In many cases the battery is more expensive than the system it is backing up. Hence we need to adopt all practical measures to conserve battery life.
As per manufacturer's data sheets, a 12V rechargeable lead-acid battery should be operated within 10. IV and 13.8V. When the battery charges higher than 13.8V it is said to be overcharged, and when it discharges below 10.IV it can be deeply discharged. A single event of overcharge or deep discharge can bring down the charge-holding capacity of a battery by 15 to 20 per cent.
It is therefore necessary for all concerned to monitor the charge level of their batteries continuously. But, in practice, many of the battery users are unable to do so because of non-avail­ability of reasonably-priced monitoring equipment. The circuit idea presented here will fill this void by providing a circuit for monitoring the charge level of lead-acid batteries continuously. The circuit possesses two vital features:
First, it reduces the requirement of human attention by about 85 per cent.
Second, it is a highly accurate and sophisticated method.
Input from the battery under test is applied to LM3914 1C. This applied voltage is ranked anywhere between 0 and 10, depending upon its magnitude. The lower reference voltage of 10.IV is ranked '0' and the upper voltage of 13.8V is ranked as '10.' (Outputs 9 and 10 are logically ORed in this circuit.) This calibration of reference voltages is explained later.
1C 74LS147 is a decimal-to-BCD priority encoder which converts the output of LM3914 into its BCD complement. The true BCD is obtained by using the hex inverter 74LS04. This BCD output is displayed as a decimal digit after con­version using IC5 (74LS247), which is a BCD-to-seven-segment decoder/driver. The seven-segment LED display (LTS-542) is used because it is easy to read compared to a bar graph or, for that matter, an analogue meter. The charge status of the battery can be quickly calculated from the display. For instance, if the display shows 4, it means that the battery is charged to 40 per cent of its maximum value of 13.8V.
The use of digital principles enables us to employ a buzzer that sounds whenever there is an overcharge or deep discharge, or there is a need to conserve battery charge. A buzzer is wired in the circuit such that it sounds whenever battery-charge falls to ten per cent. At this point it is recommended that unnecessary load be switched off and the remaining charge be conserved for more important purposes.
Another simple combinational logic circuit can also be designed that will sound the buzzer when the display shows 9. Further charging should be stopped at this point in order to pre­vent overcharge.
The circuit is powered by the battery under test, via a voltage regulator 1C. The circuit takes about 100 mA for its operation.
For calibrating the upper and lower reference levels, a digital multimeter and a variable regulated power supply source are required. For calibrating the lower reference voltage, follow the steps given below:
Set the output of power supply source to 10. IV.
Connect the power supply source in place of the battery.
Now the display will show some reading. At this point vary preset VR2 until the reading on the display just changes from 1 to 0.
The higher reference voltage is calibrated similarly by setting the power supply to 13.8V and varying preset VR1 until reading on the display just changes from 8 to 9.

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