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This is a variation on the astable multivibrator. Circuit was recently developed to test for N-mosfets(the power kind e.g irf830)... [read more]

A Battery-status Indicator circuit can be useful, mainly to monitor portable Test-gear instruments and similar devices. LED D1 flashes to attire the user's attention, signaling that the circuit is running, so it will not be left on by mistake. The circuit generates about two LED flashes per second, but the mean current drawing will be about 200µA. Transistors Q1 and Q2 are wired as an uncommon complementary astable multivibrator: both are off 99% of the time, saturating only when the LED illuminates, thus contributing to keep very low current consumption.... [read more]

This is a combination digital clock timer and solar panel charge controller used to maintain a deep cycle battery from a solar panel. The timer output is used to control a 12 volt load for a 32 minute time interval each day.... [read more]

In Greek mythology, a siren was a demonic being (half bird, half woman). Later on this idea was transformed in art into a mermaid: a combination of a fish and a woman. Mechanical and electromechanical versions were invented even later, and electronic models were developed in the last century. Sirens are characterized by their ability to produce sounds that attract attention. With the exception of the flesh-and-blood models, they are thus used to warn people in a particular area of impending danger. The electronic versions are the most suitable for DIY construction.... [read more]

Here is a simple but inexpensive inverter for using a small soldering iron (25W, 35W, etc) In the absence of mains supply. It uses eight transistors and a few resistors and capacitors. Transistors Q1 and Q2 (each BC547) form an astable multivibrator that produces 50Hz signal. The complementary outputs from the collectors of transistors Q1 and Q2 are fed to pnp Darlington driver stages formed by transistor pairs Q3-Q5 and Q4-Q6 (utilising BC558 and BD140).... [read more]

In this small switching power supply, a Schmitt trigger oscillator is used to drive a switching transistor that supplies current to a small inductor. Energy is stored in the inductor while the transistor is on, and released into the load circuit when the transistor switches off. The output voltage is dependent on the load resistance and is limited by a zener diode that stops the oscillator when the voltage reaches about 14 volts. Higher or lower voltages can be obtained by adjusting the voltage divider that feeds the zener diode. The efficiency is about 80% using a high Q inductor.... [read more]