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This small transmitter uses a hartley type oscillator.... [read more]

A different circuit of electronic lock very simple, one and does not need a lot of materials in order to it is manufactured.... [read more]

This NiCd battery Charger can charge up to 7 NiCd batteries connected in series. This number can be increased if the power supply is increased with 1.65V for each supplementary battery. If Q2 is mounted on a proper heatsink, the input voltage can be increased at a maximum of 25V. Unlike most of comercial NiCd chargers available on the market, this charger has a reverse polarity protection. Another great quality is that it does not discharge the battery if the charger is disconnected from the power supply.... [read more]

The heater element (not shown) is connected in series with two back to back 16 amp SCRs (not shown) which are controlled with a small pulse transformer. The pulse transformer has 3 identical windings, two of which are used to supply trigger pulses to the SCRs, and the third winding is connected to a PNP transistor pair that alternately supply pulses to the transformer at the beginning of each AC half cycle. The trigger pulses are applied to both SCRs near the beginning of each AC half cycle but only one conducts depending on the AC polarity.... [read more]

Here's a circuit to create a buzzcoil using a standard automotive ignition coil. A 556 dual timer is used to establish the frequency and duty cycle of the coil current. One of the timers is used as an oscillator to generate the 200 Hz rectangular waveform needed to control the (IRF740 MOSFET) while the second timer switches the oscillator on and off as the breaker points open and close (closed = on). The result is a steady stream of sparks from the ignition coil spaced about 5 milliseconds apart while the breaker points are closed.... [read more]

Capacitive touch sensors are based on the electrical capacitance of the human body. When, for example, a finger comes close to the sensor, it creates a capacitance to Earth with a value of 30 to 100 pF. This effect can be used for proximity detection and touch-controlled switching. Capacitive switches have clear advantages compared to other types of touch switches (for example 50 Hz or 60 Hz detection or resistance detection), but are often more complex to implement.... [read more]