Privacy phone

Undesired listening-in to phone conversations may be prevented by the present circuit, which requires only two components to protect a telephone. In each telephone to be protected, a traic is in each telephone to be protected, a triac is inserted in series with the line. A diac is connected between the anode and the gate[…]

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Multi-colour-led

Multi-color-led: It had to come: an LED that can produce all visible colors. It is the Everlight Type 339-1 VRKG-BBW. In fact, it consists of four LEDs in one case: one red, one green, and two blue.When these LEDs are driven into varying brightnesses, all visible colors and white can be produced. The circuit described[…]

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Variable differential amplifier

In a traditional differential amplifier with feedback to the -ye (inverting) input of an operational amplifier and a potential divider at the +ve (non-inverting) input. it is tricky to make the amplification variable. This is because the feedback network and the potential divider need to be each other’s image to ensure satisfactory suppression of the[…]

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PWM motor control

Pulse width modulation (PWM) is ad ideal for controlling small electric PCB drills that draw currents of up to 2 A. Larger currents are possible if T2 gets additional cooling and the value of C2 is increased. The design also makes use of the fact that the drill works with a small d.c. motor whose[…]

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