0 Car Headlight with Delay Circuit

What this circuit does is when you push the push-button PB1, it will make your headlight turns on for several seconds or minutes then it will turn off. The idea of this is when you push PB1, the capacitor C1 will charge and transistors Q1 and Q2 are on. During this instant, the bulb is on. When PB1 is open, the charge will drain to the resistors R1 and R3 until the capacitor voltage drops to a certain voltage that will turn off the transistor Q1 (bulb is off). Increasing the value of capacitance increases the duration of the delay. The circuit is very similar to Delay Switch using Transistor and Delay Off Circuit.

Pinout of Q2 (BC327, 9012)

Pinout of Q1 (2N2222, 9013)

Part List:
R1 - 3.9 kilo ohms 1/4W
R2 - 1.2 kilo ohms 1/4W
R3 - 1.2 kilo ohms 1/4W
C1 - 47uF electrolytic capacitor rated 16V
D1 - 1N4001 or similar diode
Q1 - 2N2222, 9013 or similar NPN transistor
Q2 - BC327, 9012 or similar PNP transistor
RELAY - 12V relay with internal resistance 100 to 500 ohms
BULB - 12V  bulb
PB1 - any Push-button

0 Delay Switch using Transistor

This simple delay switch is made up only by transistors and has very minimal parts. The function of this circuit is the combination of delay on switch circuit and delay off circuit, but much simple compared to the two. This project is very helpful in delay off or on in the car lighting system and other device powered by 12V battery.

Circuit Operation
Initially, the lamp is off and capacitor has no charge. At the moment the switch SW is closed, the capacitor charges and the voltage across it increases at a rate dependent primarily to the value R1 and C1. When the voltage across C1 is enough to trigger the transistor Q2, the lamp starts to light up. The same thing happens when the switch is open, the capacitor discharges to R4. When the voltage across the capacitor is drops, the Q2 turns off. Thus increasing the values of R1 and C1 increases the delay of turning the circuit ON (4 sec) while C1 and R4 combination determines the delay in turning the circuit OFF.

delay switch schematic

Part List:
R1  - 22 kilo ohms 1/4W
R2 - 120 kilo ohms 1/4W
R3 - 56 kilo ohms 1/4W
R4  - 47 kilo ohms 1/4W
C1 - 47uF electrolytic capacitor rated 16V
Q1 - 2N2222, 9014, 9013 or similar NPN transistor
Q2 - IRF530 or any NMOS minimum current 5A
SW - any switch available
Lamp - lamp or any DC devices

Part Pinout: Click to diagrams to enlarge

IRF530 pins

2N2222 and NPN transistor pins

2 Car Brake Light Circuit

A simple tail and brake light circuit for cars and vehicles using LED. When the vehicle is slowing down, switch s1 will be closed and LED will illuminate in low light. The LEDs will consume about 10mA each. When brake is applied, the switch s2 will closed and allowing the LED to illuminate at full brightness. This time the LEDs will consume 25mA current each. The circuit employs a constant current method, the same method used in the cheap power led driver circuit.
The current drawn by every LED is given by the simple equations:
Current on slowing down = 0.3/R2; and Current on brake = 0.3/R3  all current in Amperes

brake light circuit

2N2222 pinout

Part List:
R1 - 1.2 kilo ohms 1/4W
R2 - 30 ohms 1/4W
R3 - 12 ohms 1/4W
D1, D2 - 1N4001, 1N4004 or similar silicon diode
LED - red LED (3mm or 5mm) or any low power LED of your choice
Q1 - 2N2222, CS9013 or similar NPN transistor (higher power the better)
Bat - 12V car battery

Note: If your are planing to use power LEDs or modify the circuit to cater more LEDs, just replace the transistor with higher power capacity, and replace the values of R2 and R3 using the formula presented above.

34 12V Battery Charger ( simple and automatic)

This is a modification of 24V battery charger to cater 12V battery that requires higher charging current. Unlike the automatic 12V battery charger, this one is simpler and no comparator needed. It is more efficient also and less heating even at higher charging current. It automatically turns the charging off when the battery has reached its full charges voltage ( Vfull-charge =VDz + 1.4). The LED will light up when fully charged.

12V charger schematic

Part List :
R1 - 3.3 kilo ohms 1/4W
R2, R3 - 1.2 kilo ohms 1/4W
R4 - 5.6 kilo ohms 1/4W
R5 - see Charging Current vs R5 table below
LED - red or any 3mm or 5mm LED
Q1, Q2 - 2N2907, CS9012, 2N4403 or similar PNP transistor
Q3 - 2N2222, CS9013, 2N5551, or similar NPN transistor
Q4 - FQP27P06 or any P-channel Mosfet with higher capacity
D1 - 1N4001, 1N4004 or similar diode
Dz - 1N5242B, or any 12V zener diode
DC - 16VDC, 20A max AC-DC converter or DC power supply

P-channel Mosfet pinout

PNP transistor pinout

NPN transistor pinout

Charging Current vs R5

DC power supply

AC-DC converter schematic

Part List :

Transformer - 220V to 12V-0V-12V center tap 250VA

D - D2020L or any rectifier diode rated min 20A

C - 2200uF electrolytic capacitor rated 25V

Other useful chargers :

6V battery charger - good for 6V lead acid battery

12V charger - automatic type, current and voltage controlled

24V charger (simple and automatic) - similar to this circuit

Universal charger - charge any battery voltage form 1.2V up to 12v

Mobile phone charger - very simple charger for phones

0 Simple Battery Voltage Indicator for 12V Lead Acid

This simple circuit will help us monitor the voltage of a 12V lead acid battery in our vehicles. It uses only one transistor and no comparator needed unlike the battery discharge indicator circuitry.

Indicator circuit

Summary of the operation:
1. Only Red Led is on when voltage is less than 11.2V
2. Red and Green on (like orange) voltage is between 11.2V to 11.7V
3. Only Green Led is on when voltage is more than 11.7V


Part List:
D1 - 11V zener minimum 1/2W
D2 - 9.1V zener minimum 1/2W
R1, R3 - 1.2 kilo ohms 1/4W
R2, R4 - 120 ohms 1/4W
LED1 - high efficiency Red LED or any Red with 2V forward voltage
LED2 - any Green LED with 2.1V forward voltage
Q - 2N2222, BC547, CS9013 or similar NPN transistor

NPN transistor pinout

Note: You can use dual-color LED. See LED basic info to know more about the voltage drop of different LED color.

0 Lamp Flasher Circuit using FET

It can be used as lighting indicator and flasher in vehicles. Unlike the BJT based flasher, this one has higher current capacity thus can power not only LED but also bulbs or lamp.

Circuit Schematic

Part List:
Bulb - 1W to 30W bulb  rated 12V
R -  see table below
C -  see table below
Q - IRF530, IRFZ44N, or similar N-channel Power MosFet

IRF530, IRFZ44N pins

Rate of the flash:
Both bulbs flashes at the same rate or duration T but not at the same time. The duration T is approximately 0.7RC.

Current in both MosFets

RC time constant table

19 12V to 24V DC-DC Converter using 555 IC

This DC-DC converter  steps up 12V from battery to 24V DC. The converter can deliver around 2A current or can power 40W to 50W of load. Click diagram below to enlarge.

DC-DC converter schematic

The heart of the circuit is the 555 timer IC that delivers pulses to the transistor. The frequency of the output pulses is around 653Hz and operated at 55% duty cycle. The transistor Q3 and zener D2 regulates output to 24V dc. LED  is for output voltage indicator. D4, R6, D3 and C4 regulate and filter the supply for the driver IC.

Part List:
R1 - 2.7 kilo ohms 1/4W
R2 - 10 kilo ohms 1/4W
R3 - 1.2 kilo ohms 1/4W
R4 - 120 ohms 1/4W
R5 - 1.5 kilo-ohms 1/4W
R6 - 47 ohms 1/2W
LED - red or any low power LED
C1 - 220nF
C2 - 100nF
C3 - 1000uF ( higher the better) electrolytic capacitor rated 16V
L1 - min 40 turns (60t is best) #20AWG in ferrite antenna bar
D1 - 6A rated diode or higher
D2 - 1N4749A, 1N5359B or 24V zener diode (min 1W)
D3 - 1N4739A
D4 - 1N4001, 1N4002, or similar
Q1 - TIP41C or NPN transistor with min 10W power capacity
Q2 - 2N3055 or similar NPN power transistor
Q3 - TIP41C or 2N3055
555 timer IC

Part list diagrams/pinouts: click to enlarge

TIP41 or TIP31 pins

555 IC pins

2N3055 pins

Ferrite winding in antenna rod (60 turns is better)

1 Battery discharge indicator for 12V lead acid

This circuit will indicate the battery charge level, thus giving us idea when are we going to charge or replace it with a new one. Initially when a 12V (marked) lead acid  battery is fully charged, the voltage is around 12.7V (100% charge).When the battery is left uncharged for period of time, it starts to loss its charge and there come a time when the battery voltage drops  to  10.5 (0% charge).See table below for voltage vs battery charge.

battery voltage vs charge

Operation summary:
When battery voltage is above 12.2V (70%-100%), all LED is on. When voltage is between 11.7V to 12.2V (30%-60%),  only LED2 is on. When voltage drops below 11.7V, all LEDs are off.

indicator schematic

LM393 pins and internal connections

Part List:
LM393 comparator
R1 -120 ohms
R2 -560 ohms
R3 -560 ohms
R4 -12 kilo-ohms
R5 -4 kilo-ohms
R6 -2.7 kilo-ohms
R7 -2 kilo-ohms
R8 -2 kilo-ohms
D1 -5.1V zener diode
LED1,LED2 -red, orange, yellow and either LEDs

26 Automatic 12V Battery Charger

This time we are going to build an automatic charger for  12V lead acid battery. First we need to know the guidelines of a good charger for a lead acid battery and this guidelines will be our basis in our design.

According to sources  a good charging consist of three stages namely the constant current charging stage, followed by constant voltage charging and the final stage which is the float charge.

The scenario is that initially the discharged battery is charge at a constant current of about 10% to 30% of its rated capacity until it reaches to a certain voltage (around 2.3V per cell) it begins to saturate. Then this time the constant current charging is turn off and the charger employ a constant voltage charging until the current delivers to the battery drops down about 3% of its rated value.After reaching this point, the charger starts the float charging which is to compensate battery self discharge.

The diagram below shows the the three stages together with the state of voltage (yellow) and current (red). Click to enlarge.

Charging stages of Lead Acid Battery

Our Battery Charger design:
1. Meet the good charging guidelines of lead acid battery
2. Battery charger should be simple and cheap.

Charger Schematic and Operation Click to enlarge

charger circuit 

From the circuit above, the charger is composed of AC to DC converter, comparator for constant current and constant voltage control, transistors and zener diodes.
If the discharged battery has an open voltage of less than 13V, the output of  comparator U1 is open while U2 is shorted to the ground. In this case, constant current charging is implemented and controlled only by the
R3 and zener2 combination with magnitude of current to be delivered to the battery is :
Current (I) =( (Zener2 voltage)-0.7V) / R3


When the voltage of the battery reaches over 13V, U1 is shorted to ground while U2 is open. In this case, constant voltage charging is performed. The magnitude of voltage is limited and controlled only by Zener3.
Battery Voltage =  (Zener3 voltage) -1.4V

You can modify and improve the circuit by adding LED indicators and change the magnitude both voltage and current by simple using the formulas above.

Materials:
Transformer - 220V to 15V-0-15V, 15 to 20VA
R1 - 50K-ohm 1/4W resistor
R2 - 5K-ohm,1/4W resistor
R3 - 3.3-ohm 5W resistor
R4 - 3.9K-ohm 1/4W resistor
zener1 - 13V 1/2W zener diode (1N5243B)
zener2 - 4.7V 1/2W zener diode (1N5230B)
zener3 - 15V 1/2W zener diode (1N4744A)
Q1,Q3 and Q4 - NPN general purpose transistor (9013,2n222, etch)
Q2 - PNP power transistor (TIP32C or TIP42C)  pin out below
C1 - 1000uF 25V electrolytic capacitor
D - 1N4001 or any rectifier diode
U1 and U2 - dual comparator (LM393)  pin out below

TIP32 and TIP42 Pinout

LM 393 pinout