Simple Emergency Lamp Circuit Diagram

1. The circuit within the dotted line for a mini emergency light can be incorporated into any battery eliminator, provided the eliminator’s voltage is higher than the battery’s voltage.
2. For greater load (1.e. for more light through a b1gger lamp), Tl should be a power transistor such as ADl49. Diode in the circuit prevents the flow of current from battery in the emergency light to the radio during power failure. It is enough to use the switch in the radio set to tum it off.
3. However, when the power is off, the transistor gets forward biased and the lamp lights up.
4. Whenever there is power, the transistor is kept reverse biased and there is no current flowing through the collector circuit. 

 

The following circuit of a simple LED flasher can be used for any indication purpose in stereo amplifiers, tape recorders, fancy dolls etc. All components are locally available and the project would cost about Rs 12 only, apart from power supply.   A Schmitt trigger provides regenerative switching, and Rl gives the necessary charge/ discharge bistable action as Tl is switched on and off. R3 and R4 set the “on’ and ‘off times respectively. Brightness of the LED is set by Rl and Vg Depending upon the capacitor, the R-C time constant can be  adjusted. 

Simple 7-Segment Counter Circuit

1. lC3 is similarly fed from IC2. The contents of each decade counter are taken in BCD (binary coded decimal) form, fed through IC 7447 BCD to 7- segment decoder driver and displayed on the corresponding FND 507 LED display.
2. These shaped pulses_are counted by three decade chain counters using three 7490 ICs. Input is given to pin I4 of ICI and output from pin ll of this IC is fed to pin I4 of IC2.
3. Thus the contents of ICI, IC2 and lC3 are displayed one Ll (hundreds), L2 (tens) and L3 (units) I respectively. Capacitors Cl-C6 are used for noise rejection. A series of three diodes, all lN400l type, have been used for current limiting of the displays and also for maintaining the flow of current in a unidirectional way.
4. Sl resets the counter. Circuit diagram of regulated +5V supply is shown in Fig. 2. Mains voltage is stepped down to 9V AC by transformer xi, rectified by a rectifier bridge comprising four diodes (D4-D7) and regulated to +5V by ICS (7805)