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This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 - #35 magnet wire.... [read more]

These two headlight reminder circuits are easy to install and operate on the KISS (Keep It Simple Stupid) principle. The simple circuit involves adding just a 12V piezo buzzer between the lights circuit and a door switch. The buzzer sounds if the lights are left on and you open a door. The disadvantage of this simple circuit is that it's annoying to have the buzzer sound continuously if you want to leave the door open while the lights are on. The improved circuit overcomes that problem by adding a 1000µF capacitor and a parallel 100kO resistor in series with the buzzer. Now, when a door is opened, the buzzer gives a brief burst of sound only, while the 1000µF capacitor charges. The 100kO resistor discharges the capacitor when the lights are switched off.... [read more]

The mentioned shunt-feedback configuration also allows the easy addition of frequency dependent networks in order to obtain an useful, unobtrusive, switchable Tilt control (optional). When SW1 is set in the first position a gentle, shelving bass lift and treble cut is obtained. The central position of SW1 allows a flat frequency response, whereas the third position of this switch enables a shelving treble lift and bass cut.... [read more]

This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor's output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables. The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained. Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter.... [read more]

This device allows one or more lamps to illuminate at sunset and turn off at dawn.Q1 and Q2 form a trigger device for the SCR, providing short pulses at 100Hz frequency. Pulse duration is set by R2 and C1.When the light hits R1, the photo resistor assumes a very low resistance value, almost shorting C1 and preventing circuit operation. When R1 is in the dark, its resistance value becomes very high thus enabling circuit operation.... [read more]

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam.... [read more]