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This simple circuit will energize and de-energize a relay at the push of a button. Pushing the button once - will energize the relay. And pushing it a second time - will de-energize the relay. The accompanying Circuit Description offers a good introduction to the workings of the Cmos 4013.... [read more]

This light-weight gadget produces an adjustable gain on sounds picked up from the built-in high-sensitivity condenser microphone. So you can hear what you have been missing. With a 6V (4×1.5V) battery, it produces good results. As shown in Fig. 1, a small signal amplifier is built around transistor BC547 (T1).... [read more]

This simple circuit drives 6 LEDs in 'Knightrider scanner mode'. Power consumption depends mainly on the type of LEDs used if you use a 7555 (555 CMOS version).... [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]

It is a simple circuit regulated power supply, based on the known LM 723, that drive a transistor Q1 [2N3055]. The regulation of voltage, of expense becomes with potentiometer R1 from 0v-30v DC roughly. In order to we achieve 30 V, will should the transformer of supply TR1, it gives all the current that it asks the load, differently the output voltage it will be found in the levels of 26 V roughly. Essential is the use of a good heatsink for transistor Q1, as well as good quality of potentiometer in the place of R1.... [read more]

This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. You can adapt it to your own requirements as explained in the notes below.... [read more]