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For a collector follower with emitter resistor, you’ll often find that the gain per stage is no more than 10 to 50 times. The gain increases when the emitter resistor is omitted. Unfortunately, the distortion also increases. With a ubiquitous transistor such as the BC547B, the gain of the transistor is roughly equal to 40 times the collector current (Ic), provided the collector current is less than a few milliamps. This value is in theory equal to the expression q/KT, where q is the charge of the electron, K is Boltzmann’s constant and T is the temperature in Kelvin.... [read more]

This circuit generates a two-tone effect very much alike the cuckoo sound. It can be used for door-bells or other purposes thanks to a built-in audio amplifier and loudspeaker.... [read more]

You have to admit that these tiny electronic lamps are handy, and they last almost forever. Around 40 years after Nick Holanyak developed the first LED, they have become just about indispensable. Any self-respecting electronics hobbyist always has a few in his junk box. But before you use LEDs, it’s a good idea to check them out. With a LED tester, you can even do it in the dark!... [read more]

The circuit described here is that of a metal detector. The opera- tion of the circuit is based on superheterodyning principle which is commonly used in superhet receivers. The circuit utilises two RF oscillators.... [read more]

This circuit is Ideal for car use. It has ability to transform a mains adapter in to a charger . This one can be used to charge cellular phone, toys, portables, video batteries, MP3 players, ... and has selectable charge current. An LED is located in circuit to indicate charging. Can be built on a general purpose PCB or a veroboard.... [read more]

Sometimes you have a situation where you have a 5-V supply voltage but part of the circuit needs a lower supply voltage. A voltage regulator from the Texas Instruments TPS62000 family [1] is a good choice for this if the current consumption is less than 600 mA.... [read more]