Sajee tronics

Digital wall clocks, table clocks and desk clocks with pointer or LCD display are readily available in the market. Here we present a clock that can be built in a small budget using AT89C2051 microcontroller. Additional feature of the clock is that the time display is visible even in the dark. Circuit description Fig. 1 shows the circuit of the microcontroller-based clock. It comprises microcontroller AT89C2051 (IC1), inverting buffer ULN2003 (IC2), real-time clock (RTC) DS1307 (IC3), regulator 7805 (IC4), non-inverting source driver UDN2982 (IC5) and a few discrete components. Microcontoller AT89C2051 is the heart of the clock. It is an 8-bit microcontroller with 2kB Flash programmable and erasable read-only memory (PEROM), 128 bytes of RAM, 15 input/output (I/O) lines, two 16-bit timers/counters, a five-vector two-level interrupt architecture, a full-duplex serial port, a precision analogue comparator, on-chip oscillator and clock circuitry. Port pins P1.7 down through P1.1 of the mic...

Useful for vehicle owners, this gadget automatically turns on indoor/outdoor garage lights and raises an alert when an automobile enters the garage. Assume switch S2 is in ‘on’ (closed) state. When power switch S1 is turned on, the complete circuit is energised by the 12V DC supply. LED3 lights up to provide power-on indication. Simultaneously, IC3 (CD4017B) is instantly reset by the power-on-reset circuit formed by the combination of capacitor C4 and resistor R5, and green LED2 lights up as a standby indicator. As per the physical arrangement, IR rays from IR-LED fall on phototransistor T1 and it conducts to pull up the inputs of NAND gate N1 (used here as an inverter) to logic 1. As a result, the output of gate N2 goes high to make the monostable built around IC2 inactive. Now, when a vehicle moves through the door, the IR beam is interrupted and the output state of gate N2 changes from high to low state, which triggers the monostable and red LED1 (Rx on) lights up briefly. The o...

T his circuit lets you locate wire breaks, so you can cut the wire  insulation at precise points and repair the breaks. The working of the circuit is based on capacitive effects developed in a tube detector. Before detecting breaks, it is essential to know which wire has a break. This can be easily detected using a continuity tester. Once the wire having a break is detected, signals from the col lectors of transistors T2 and T3 (points A and B) have to be applied to the two ends of that wire and a tube has to be run along the wire for detecting the break point. This tube actually forms a capacitor with the test wire. When the tube crosses the break point in the wire, there is a flip in the LED glow indicating wire break.                    The circuit is built around a 555 timer IC (IC1), CMOS NAND gate CD4011 (IC2), CMOS NOR gate CD4001 (IC3) and a few discrete components. IC 555 is wired as an astable multivibrator....

This simple key-operated gate locking system allows only those persons who know the preset code to open the gate. The code is to be entered from the keypad within the preset time to operate the motor fitted in the gate. If anyone trying to open the gate presses a wrong key in the keypad, the system is disabled and, at the same time, sounds an alarm to alert you of an unauthorised entry. Figs 1 and 2 show the block and circuit diagrams of the key-operated code locking system, respectively. Connect points A, B, C, D, E, F and ground of the circuit to the respective points of the keypad. Keys S7, S16, S14 and S3 are used here for code entry, and the remaining keys are used for disabling the system. It is very important to press the keys in that order to form the code. To start the motor of the gate, press switches S7, S16, S14 and S3 sequentially. If the keys are pressed in a different order from the preset order, the system will lock automatically and the motor will not start. Fig. 1: ...

Normally, sound intensity up to 30 dB is pleasant. Above 80 dB, it becomes annoying. And if it goes beyond 100 dB, it may affect your psychomotor performance, detracting your attention and causing stress. Noise pollution may also affect your hearing ability.

Description: The ADXL345 is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16 g. Digital output data is formatted as 16-bit twos complement and is accessible through either a SPI (3- or 4-wire) or I2C digital interface. The ADXL345 is well suited to measure the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables measurement of inclination changes less than 1.0°. Several special sensing functions are provided. Activity and inactivity sensing detect the presence or lack of motion and if the acceleration on any axis exceeds a user-set level. Tap sensing detects single and double taps. Free-fall sensing detects if the device is falling. These functions can be mapped to one of two interrupt output pins. An integrated, patent pending 32-level first in, first out (FIFO) buffer can be used to store data to minimize host processor...

Usually, low-priced home stereo power amplifiers don’t have output level indicators. An output power level indicator can be added to each channel of these stereo power amplifiers. As low levels of the output power are not disturbing and damaging to the people, there is no need to add a preamplifier and low-level detector before IC LM3915. But you should know when the output power becomes considerably high. Here we present a very simple, low-cost stereo-level indicator circuit for home power amplifiers with power rating of around 0.5W. The circuit is built around two LM3915 dot/bar display driver ICs (IC1 and IC2). LM3915 senses analogue voltage levels to drive ten LEDs, providing a logarithmic 3dB/step analogue display. The voltage levels below 1V are not important because these correspond to a low level of the audio signal. Similarly, input voltage levels above 30V correspond to too high levels of the output power, which are not applicable for home power amplifiers. So the voltage...