Simple Low-Power Audio Amplifier (New)
The small-signal amplifier is generally referred to as a voltage amplifier because it usually converts a small input voltage into a much larger output voltage. The audio power amplifier works on the basic principle of converting low-power audio signal to a suitable level to be delivered to the load. This low-power amplifier circuit is useful for the amplification of sound from small-signal devices such as mobile phones, laptops or desktops.
Monitor for 6V/12V Batteries (New)
Rechargeable batteries of 6V and 12V are used in a large number of applications. It is imperative that these are maintained properly to get maximum life out of them. Further, their permissible number of charge-discharge cycles must be fully utilised. Here is a circuit that gives a visual as well as an audible alarm if the battery voltage is higher or lower than acceptable limits, so that corrective action can be taken.
Power-Saving Relay Driver (New)
In many circuits, the switching action is performed by a relay, which in turn activates an external load. The power consumed by the relay may be unsuitable for battery-powered applications. Here is a simple solution using some inexpensive components to considerably save power.
Simple Tester for 74xx04 and 74xx14 ICs (New)
The integrated circuits (ICs) 74xx04 and 74xx14 are very frequently used and reused during circuit design. Here xx stands for HC, HCT, AC and LS, etc. Sometimes, the internal inverters of these ICs get damaged. So, it is very important to test these ICs before initiating any experiment and sometimes during the experiments.Presented here is a simple circuit which can test these ICs statically and dynamically.
Efficient LED Blinking for Embedded Systems
Smart hardware design can simplify the embedded software and make it more reliable. Designers use blinking LED signals to indicate different status and for inbuilt testability. Making an LED array blink requires an individual software loop for each LED or an individual timer and specific software to serve it. This can be an issue in a system that uses low-level MCUs which provide limited resources.
Presented here is a simple pedometer circuit. It measures the distance covered by you while walking. It may not work very well for running!
Multi-tone Configurable Alarm
Presented here is a multi-tone configurable alarm that can be activated by temperature and other physical parameters. Its output tone can be selected through different switch combinations. Such an alarm is highly desirable when multiple alarms are present in the same area. Different tones can be selected for different alarms so that you can easily know which alarm has triggered. The alarm in this circuit is activated by temperature.
Precision 1Hz Clock
This precision 1Hz clock uses just two ICs and one junction field-effect transistor (JFET) in conjunction with a commonly available crystal and a handful of other passive components.
Subwoofer for Cars
This system needs to be attached to an existing car stereo amplifier to add extra 'boom effect' to the music. It has a dedicated loudspeaker with a power amplifier to boost low frequencies that are normally omnidirectional.
Intelligent Water Pump Controller with Water-level Display
Most of the circuits for multi-level indication/control of water in tanks employ a bunch of wires running between the circuit and the overhead tank, which accounts for almost half the cost of the entire project. Here is an intelligent scanned water-level indicator-cum-pump controller circuit that utilises just four wires to the overhead tank to indicate nine different levels.
Infrared Proximity Detector
This proximity detector using an infrared detector (Fig. 1) can be used in various equipment like automatic door openers and burglar alarms. The circuit primarily consists of an infrared transmitter and an infrared receiver.
Here is a simple water-level indicator for overhead tanks that uses three LEDs (LED1, LED2, and LED3) to indicate minimum, middle, and maximum water levels in the tank.
PWM-Based Speed Control for DC Motors
There are several methods for controlling the speed of DC motors. One simple method is to add series resistance using a rheostat. As considerable power is consumed in the rheostat, this method is not economical. Another method is to use a series switch that can be closed/opened rapidly. This type of control is termed as chopper control. We’ve described here a PWM-based chopper circuit that smoothly controls the speed of general-purpose DC motors.
LED Sand-Glass Timer
This circuit simulates the old sand-glass timer. A total of 32 LEDs create the effect of sand grains passing from the upper half of sand-glass to its lower half.
Garage Light and Security Control
Useful for vehicle owners, this gadget automatically turns on indoor/outdoor garage lights and raises an alert when an automobile enters the garage.
Presented here is a simple locker security alarm that can be used to protect a locker from unauthorised access. The circuit is low-cost and forms a fool-proof alarm that receives its control signal from a standard reed switch. The circuit works off a 12V DC power supply.
RJ45 Cable Tester
Described here is a simple RJ45 cable tester circuit which can be used for testing the RJ45 network cables. The circuit can check both straight-through and crossover-type RJ45 network cables. This is a low-cost tester designed using easily available components. Fig. 1 shows the difference between straight-through and crossover network cables.
We are all so busy with our daily lives that we forget to take our medicines on time, which can have several ill effects on our health. The circuit described here helps in making a simple reminder that allows you to set an alert for the medicines that you need to take. The device flashes an LED or rings a buzzer at the selected time intervals.
Automatic Room-lock and Lights circuit
This circuit counts and indicates up to nine persons present in the room and automatically locks the door and switches off lights as soon as they leave. It automatically switches on the lights when the first person enters the room. The circuit can be used as a power-saving device and a security device to prevent unauthorised entry in the room, especially in a business meeting room.