Posted on Sep 20, 2012

A single op amp-one of four contained in the popular LM324-is operating in a variable pulsewidth, free-running squarewave oscillator circuit, with its timed output driving two transistors that control the on/ off cycle of the tape-drive motor. The Dscillator` s positive feedback path holds the secret to the successful operation of the variable on/ off timing signal. The two diodes and pulsewidth potentiometer R8 allows the setting of the on and off time, without affecting the oscillator`s operating frequency.

Click here to download the full size of the above Circuit.

One diode allows only the discharge current to flow through it and the section of R8 that it"s connected to. The other diode, and its portion of R8, sets the charge time for the timing capacitor, C3. Since the recorder"s speed is controlled by the precise off/on timing of the oscillator, a simple voltage-regulator circuit (Ql, R3, and D4) is included. Connecting the speed control to most cassette recorders is a simple matter of digging into the recorder and disconnecting either of the· motor"s power leads, the ground or common side might be best, and connecting the recorder through a length of small, shielded ci!ble to the control circuit. In some recorders, a remote input jack is furnished to remotely tum on and off the recorder. Before going in and modifying a recorder with a remote jack, try connecting the circuit to the external remote input.

Leave Comment

characters left:

New Circuits



Popular Circuits

Solar powered robot
Power Supply Monitor /Memory Protector
Vlf Whistler Receiver Circuit
Arduino RFID Door Lock
original electric furnace
Gas Leakage Sensor Alarm Circuit Engineering Project using 555 Timer and MQ6 SEN 1327 Gas Sensor Module
Amplifier circuit from tube radio
Voice changer circuit diagram electronic projects using RTS0072B
Single Zone AlarmCircuit - Project
Line Following Robot circuit
Tachometer circuit diagram of a multiplier