Simple Car Battery Charger

Simple Car Battery Charger
This very simple circuit uses a transformer ,two diodes , a capacitor and an ammeter.
To charge a battery just connect the + and - terminals of the circuit to the corresponding terminals of the battery.
When the battery is not charged, the ammeter reading shows 1-3 amps.
When the battery is fully charged the ammeter reads Zero or nearly zero, after which the battery should be removed from the
charger.
The circuit is a full wave rectifier using 2 diodes for rectification. The capacitor is used for smoothing.
I think the circuit works fine without the capacitor since the battery itself acts a BIG capacitor. But when you are using the
circuit to supply 12V (as a battery eliminator) the capacitor needs to be present.
Care should be taken NOT to reverse the + and - terminals while connecting it to the battery.
Self switching Power Supply Click here for the circuit diagram
One of the main features of the regulated power supply circuit being presented is that though fixed-voltage regulator LM7805 is used in the circuit, its output voltage is variable. This is achieved by connecting a potentiometer between common terminal of regulator IC and ground. For every 100-ohm increment in the in-circuit value of the resistance of potentiometer VR1, the output voltage increases by 1 volt. Thus, the output varies from 3.7V to 8.7V (taking into account 1.3-volt drop across diodes D1 and D2).
Another important feature of the supply is that it switches itself off when no load is connected across its output terminals. This is achieved with the help of transistors T1 and T2, diodes D1 and D2, and capacitor C2. When a load is connected at the output, potential drop across diodes D1 and D2 (approximately 1.3V) is sufficient for transistors T2 and T1 to conduct. As a result, the relay gets energised and remains in that state as long as the load remains connected. At the same time, capacitor C2 gets charged to around 7-8 volt potential through transistor T2. But when the load is disconnected, transistor T2 is cut off. However, capacitor C2 is still charged and it starts discharging through base of transistor T1. After some time (which is basically determined by value of C2), relay RL1 is de-energised, which switches off the mains input to primary of transformer X1. To resume the power again, switch S1 should be pressed momentarily. Higher the value of capacitor C2, more will be the delay in switching off the power supply on disconnection of the load, and vice versa.
Though in the prototype a transformer with a secondary voltage of 12V-0V, 250mA was used, it can nevertheless be changed as per user’s requirement (up to 30V maximum. and 1-ampere current rating). For drawing more than 300mA current, the regulator IC must be fitted with a small heat sink over a mica insulator. When the transformer’s secondary voltage increases beyond 12 volts (RMS), potentiometer VR1 must be redimensioned. Also, the relay voltage rating should be redetermined.
Light Flasher -Naveen P N Click here for the circuit diagram
This is a very basic circuit for flashing one or more LEDS and also to alternately flash one or more LEDs.
It uses a 555 timer setup as an astable multivibrator with a variable frequency.
With the preset at its max. the flashing rate of the LED is about 1/2 a second. It can be increased by increasing the value of the capacitor from 10uF to a higher value. For example if it is increased to 22uF the flashing rate becomes 1 second.
There is also provision to convert it into an alternating flasher. You just have to connect a LED and a 330ohm as shown in Fig.2 to the points X and Y of Fig.1. Then both the LEDs flash alternately.
Since the 555 can supply or sink in upto 200mA of current, you can connect upto about 18 LEDS in parallel both for the flasher and alternating flasher (that makes a total of 36 LEDs for alternating flasher).
Automatic Dual output Display Click here for the circuit diagram
This circuit lights up ten bulbs sequentially, first in one direc- tion and then in the opposite direction, thus presenting a nice visual effect. In this circuit, gates N1 and N2 form an oscillator. The output of this oscillator is used as a clock for BCD up/down counter CD4510 (IC2). Depending on the logic state at its pin 10, the counter counts up or down. During count up operation, pin 7 of IC2 outputs an active low pulse on reaching the ninth count. Similarly, during count-down operation, you again get a low-going pulse at pin 7. This terminal count output from pin 7, after inversion by gate N3, is connected to clock pin 14 of decade counter IC3 (CD4017) which is configured here as a toggle flip-flop by returning its Q2 output at pin 4 to reset pin 15. Thus output at pin 3 of IC3 goes to logic 1 and logic 0 state alternately at each terminal count of IC2. Initially, pin 3 (Q0) of IC3 is high and the counter is in count-up state. On reaching ninth count, pin 3 of IC3 goes low and as a result IC2 starts counting down. When the counter reaches 0 count, Q2 output of IC3 momentarily goes high to reset it, thus taking pin 3 to logic 1 state, and the cycle repeats. The BCD output of IC2 is connected to 1-of-10 decoder CD4028 (IC4). During count-up operation of IC2, the outputs of IC4 go logic high sequentially from Q0 to Q9 and thus trigger the triacs and lighting bulbs 1 through 10, one after the other. Thereafter, during count-down operation of IC2, the bulbs light in the reverse order, presenting a wonderful visual effect