OBJECTIVE   Timer IC 555 is versatile general-purpose linear integrated circuits and is thus the most widely used one. It is indeed a favourite with hobbyists. It is mostly used either as a monostable or an astable multivibrator. In this project activity, we shall present some modified circuits for monostable and astable operation of timer IC 555 and see for ourselve show these changes simplify design. In two of the four different circuits given here, the circuits have been so modified as to yield very simple and design friendly expressions for the monostable and astable operations. In case of modified astable circuit, the expressions for output frequency becomes f = 1/RC where (R) is charge path resistance equal to the discharge path resistance and (C) is the capacitance. In a read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

OBJECTIVE   Here is a simple and very easy to build alarm siren producing gadget capable of producing five different types of siren tones. The gadget is built around a single IC 556 which is nothing but a dual IC timer 555.That is, it has two independent 555s   within the same package. The type of siren can be selected from an appropriate combination of switches to be closed given in the accompanying table. The gadget could also be constructed using two 555s in place of one 556.   CIRCUIT DESCRIPTION For a clear understanding of this circuit functioning, it is very important to identify those pins in IC556 that represent two independent 555′s. IC555 has eight terminals namely the COMMON (Pin-1), TRIGGER (Pin-2), OUTPUT (Pin-3), RESET (Pin-4), CONTROL (Pin-5), read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

OBJECTIVE Wide fluctuations in the AC mains voltage is a very common problem in India. You should not be surprised if some one tells you that the voltage fluctuation could be as much as from 150 volts to 290 volts. Although, majority of our electrical and electronic appliances and gadgets have some kind of voltage stabilization internals built-in, yet more than 90 percent of the faults in these gadgets occur due to these power fluctuations. This simple test gadget can give you real time monitoring of the AC mains voltage in the form of glowing LEDS. It can give you the visible indication of AC mains voltage over a range of 170 volts to 280 volts in steps of 10 volts. There are 12 LEDS numbered from LED-! to LED-12. For input AC mains voltage of less than 170 volts, all LEDs remain read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

Objective The objective here is to construct an emergency fluorescent light circuit that requires neither a choke nor a starter unlike conventional mains   operable fluorescent light. Such emergency lighting units having different lighting power capabilities are available in abundance in the market. The circuit given here is simple and highly| efficient. It operates from a 6V rechargeable battery (Lead-Acid type). The battery is trickhigh-freuency-emergency-fluorescent-lightle charged when the mains is present. The battery with a capacity of 6Ah (this is the battery used in this project) is capable of providing uninterrupted lighting for four hours in the absence of mains. The switch over is fully automatic i.e. When the mains goes OFF, the battery comes into the lighting circuit read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

  Objective It is an ideal project for those who want to build something that not only teaches them something but also gives them lot of fun. As the title suggests, this gadget can be used to measure quantitatively the reaction time of an individual. The reaction time can be measured in two different settings: In the first setting, the reactiontime can be measured upto a maximum of 99ms with a resolution of 1ms. In the second setting, the reaction time can be measured upto a maximum of 990ms with a resolution of toms. You can try this gadget with your friends and relatives and find out how quickly they react to a given situation.You can, try this with yourself too at different times and when you are In different states of mind and see the difference yourself. Circuit description read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

OBJECTIVE The objective here is to build a 3l/2-digit digital voltmeter with a standard instrument sized LED display. It may be mentioned here that the IC type number ICL7107 is almost universally used for digital voltmeter application and the cirduit shown in Fig. 18.1 is basically what you would discover inside any digital panel meter with a 3l/2-digit LED display. The said voltmeter has beep designed to operate from AC mains to generate regulated +5VDC and -5DVC for the circuit. Digital panel meters with an LED display usually operate from AC mains due to significant current drive requirement of LED displays. There is a separate power supply section (Fig. 18.2) that generates regulated +5VDC and -VDC It is also worthwhile   mentioning here that this circuit can also be used for read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

OBJECTIVE The project under construction here is a DIGITAL STOPWATCH that could count time up to a maximum of 99.9 seconds with a resolution of 0.1sec (or in steps of 0.1 sec) or up to a maximum of 999 seconds with a resolution of 1 second. This has been possible by having two clock frequency options, a 10Hz clock and a 1Hz clock. This gadget can be used to accurately measure short time intervals. It is portable and operates from four rechargeable Ni-Cd cells. CIRCUIT DESCRIPTION IC1 (MM5369) is a popular IC used for generating clock pulses in digital time pieces. lC-1 along with resistors (R1), capacitors (C1) and (C2) and crystal generates a 60 Hz clock signal at its output (Pin-1). This 60Hz clock signal is passed on to the clock input of IC-3 (CD4018B) via an arrangement of read more

If you enjoyed this post, make sure you subscribe to my RSS feed!

OBJECTIVE A simple, easy to build portable all electronic resistance meter that can be used to accurately measure resistances up to a maximum of 1MΩ is the project under construction here. The circuit operates from twin 9V batteries. The resistance meter has a linear scale and the zero resistance point appears on the extreme left end of the scale. Another significant feature of this meter is that it can be used to measure resistances without   actually taking them out of the circuit.It has six different selectable ranges that permit resistance measurement in decades of (i) 1Ω to 10 Ω (ii) 10 Ω  t0 100 Ω  (iii) 100 Ω  to 1K (iv) 1K to 10K (v) 10K to 100K and (vi) 100K to 1M CIRCUIT DESCRIPTION The measurement of resistance in this meter is in terms of voltage developed read more

If you enjoyed this post, make sure you subscribe to my RSS feed!