One Transistor Radio

Here is a simple circuit for a one transistor Audion type radio powered by a 1.5 V battery. It employs a set of standard low-impedance headphones with the headphone socket wired so that the two sides are connected in series thus giving an impedance of 64 Ω. The supply to the circuit also passes through […]

Transistorised Code Lock With Torch

This electronic lock for domestic use opens only when you connect the right combination of five switches. There are twelve switches in total. If you connect a wrong combination, the lock remains closed. At night, flip switch S3 to ‘on’ position in order to enable the torch. In the daytime, flip it back to ‘off’ […]

Mains Manager

Very often we forget to switch off the peripherals like monitor, scanner, and printer while switching off our PC. The problem is that there are separate power switches to turn the peripherals off. Normally, the peripherals are connected to a single of those four-way trailing sockets that are plugged into a single wall socket. If […]

Bipolar Transistor Tester

This tester is primarily meant to test bipolar transistors. It can indicate the type of the transistor as well as identify its base, collector and emitter pins. The circuit is very simple. The direction of current flow from the terminals of the transistor under test (TUT) is indicated by a pair of LEDs (green-red). An […]

In Circuit Transistor Checker

This simple circuit has helped me out on many occasions. It is able to check transistors, in the circuit, down to 40 ohms across the collector-base or base-emitter junctions. It can also check the output power transistors on amplifier circuits. Circuit operation is as follows. The 555 timer ( IC1 ) is set up as […]

Cheap And Cheerful Transistor Tester

By using a simple visual indicating system, this small transistor tester allows you to run a quick ‘go/non-go’ check on NPN as well as PNP transistors. If the device under test is a working NPN then the green LED (D1) will flash, while the red counterpart will flash for a functional PNP device. However if […]

Low-Noise Microphone Amplifier (OP270E)

The signal from a microphone is two weak for a standard line input. This low-noise DC-coupled microphone amplifier provides a solution for anyone who wants to connect a microphone to his or her hi-fi installation. As can be seen from the schematic diagram, a good circuit does not have to be complex. A differential amplifier […]

Economical Transistor Radio

The schematic diagram shows an audio stage with a common-collector circuit. This does not damp the tuned circuit, but instead actually increases its response. This yields good sensitivity and selectivity. Due to the low supply voltage, the subsequent audio amplifier needs three transistor stages. The volume is adjusted using the potentiometer. This radio works well […]

Practical Circuit Design Technique in Boosting Current Limit of CLDs by Using Transistor Current Gain

If you find that such an impractical way by just adding the Current Limiting Diodes (CLD) to obtain high current level, the following article may help you regarding the informations within. This article will describe you with a simplified description of practical circuit design technique in boosting current limit by using transistor current gain. What […]