12V 10A High current Power Supply with battery backup

The full circuit diagram of the 12V 10A Power Supply is shown in Fig.1.Power of about 18V to 25V is applied to screw terminals pins 1 (+V) and 2 (–V).Although the power supply was originally designed to run packet radio transceivers, the unit is not just confined to this type of radio. In fact, any radio can be used with this power supply. It can also be used as a main source of power; ie the battery, or used as a standby source of power in the event of a power failure. There would be a float charge for the battery when mains voltage is applied, and the battery can be relied on to supply current to equipment when the mains supply fails.

The input current to the circuit is limited by a 5A fuse (FS1) for protection purposes. Relay RLA is a small ‘homemade’ reed type that is set to close the contacts when the current drawn through this relay coil is in the order of about 1.5A. When this occurs, RLA’s contacts close, current is drawn through resistor R1, LED1, R2 and onto R3. The voltage across resistor R3 is sufficient to turn on FET TR2, which supplies power to a 12V cooling fan.

Universal Remote Control Receiver

The circuit diagram shown in Fig.1 uses a PNA4602M IR detector to receive an IR signal from  the remote control. It’s a neat device, which contains an IR receiver, amplifier and demodulator together in a single 3-pin package, and it’s normally used in circuits where you want to decode an IR remote control signal. 

The way the circuit (Fig.1) works is as follows. When there is no IR coded signal present, the output pin of IC1 remains high. This high signal is fed to the trigger input of the 555 timer (IC2), which being configured as a monostable timer, prevents the timer operating. 

Whenever you briefly press any key on the old remote control its IR signal is received by IC1 and output pin 1 produces a train of fast moving high and low pulses, which mimic the IR signal code sent by the remote control. We are not interested in this code, but as soon as the signal switches low it triggers the monostable timer IC2 and its output pin 3 goes high for a short period of time, set by resistor R2 and capacitor C2.

LDR Based Water Pump Controller

Here is a simple solution for automatic pumping of water to the overhead tank. Unlike other water-level indicators, it does not use probes to detect the water level and hence there is no probe corrosion problem. It has no direct contact with water, so the chance of accidental leakage of electricity to the water tank is also eliminated.

Two important advantages of the circuit are that the water level never goes below a particular level and no modification in the water tank is required. Fig. 1 shows the circuit of the water pump controller. The circuit uses an LDR-white LEDs assembly to sense the water level. It forms a triggering switch to energise the relay for controlling the pump. The LDR-LEDs assembly (shown in Fig. 2) is fixed on the inner side of the cap of the water tank without making contact with water. The light reflected from the water tank is used to control the resistance of LDR1.

Portable Lamp Flasher

Here is a portable, high-power incandescent electric lamp flasher. It is basically a dual flasher (alternating blinker) that can handle two separate 230V AC loads (bulbs L1 and L2).

The circuit is fully transistorized and battery-powered. The free-running oscillator circuit is realized using two low-power, low-noise transistors T1 and T2. One of the two transistors is always conducting, while the other is blocking. Due to regular charging and discharging of capacitors C1 and C2, the two transistors alternate between conduction and non-conduction

states.

The collector of transistor T1 is connected to the base of driver transistor T4 through current-limiting resistor R5. Similarly, the collector of transistor T2 is connected to the base of driver transistor T3 through limiting resistor R6. These transistors are used to trigger Triac1 and

Triac2 (each BT136) through optotriacs IC1 and IC2, respectively, and switch on the power supply to external loads L1 and L2. IC1 and IC2 operate alternatively at a low frequency

determined by the values of capacitors C1 and C2.

Long-Range IR Transmitter

Most of the IR remotes work reliably within a range of 5 metres. The circuit complexity increases if you design the IR transmitter for reliable operation over a longer range, say, 10 metres. To double the range from 5 metres to 10 metres, you need to increase the transmitted power four times.

If you wish to realise a highly directional IR beam (very narrow beam), you can suitably use an IR laser pointer as the IR signal source. The laser pointer is readily available in the market. However, with a very narrow beam from the laser pointer, you have to take extra care, lest a small jerk to the gadget may change the beam orientation and cause loss of contact.