Assembly of the F&DARC Square Wave Generator/Bridge

This project combines several features in one compact unit. The fundamental driver consists of a NE 555 square wave generator. During development, consideration and a certain amount of experimentation was given to the construction of a square wave unit using discrete components. Investigation showed however that the geometry of the square wave pro
Assembly of the F&DARC Square Wave Generator/Bridge - schematic

duced was so poor that additional complexity would be needed in the form of a Schmitt trigger circuit. In order to keep the unit as simple as possible, and at the same time produce a usefully clean and symmetrical square wave which could have further applications, the discrete approach was abandoned. The final square wave generator using an NE555 IC has both a low component count and is simple to construct; it produces an excellent square wave, rich in harmonics (for signal tracing), and ample output to drive the capacitance bridge. The whole unit in its basic form can be constructed on a piece of PCB only three inches square. If a capacitance substitution box - which in itself also has further application - is added, to extend the range and convenience of the bridge, the entire unit occupies 3" x 6". The unit is powered by a 9 volt PP3 battery. The following instructions include the circuit, component list, comprehensive layout and connection diagrams, and photographs of the completed prototype (basic) unit. The circuit diagram is given in Fig. 1, and is of the project in its basic form, i. e. without the capacitor substitution box. The circuit of the capacitor substitution box is shown in Fig. 2. With the the values of resistors used, this circuit oscillates at about 1 kHz, producing a square wave of approximately equal mark / space ratio. Should it be necessary at a later date, the frequency may be altered between about...

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