Circuit :  Andy Collinson
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Description:
A very basic square wave generator using a CMOS 4011 NAND gate.


Notes
Using two gates from a CMOS 4011 NAND chip, a simple squarewave oscillator can be made. Pinouts for the CMOS 4011 can be found in the practical section click here. For convenience the CMOSD 4011 pinout is shown below: All unused inputs should be tied to ground. The circuit uses just two gates so for example you could use the left hand gates which use pins 1 to 6. The right hand gates unused inputs should connect to ground, that is pins 8,9,12 and 13. Not shown in the schematic pin 14 is Vcc and pin 7 is the circuit ground.

Alternatively a TTL 7401 or Hi-Speed Schottky 74LS01 chip can also be used. In this circuit the mark space ratio can also be interdependently controlled by varying the value of the resistors. The rise and fall times of the output pulses depend on the operating voltage of the IC and type of IC, but will be typically in the order on tens of nanoseconds.

Typical Output Waveform
A typical output waveform is shown below: LTSpice Simulation
The circuit that produced the above output graph can be downloaded here.
To use, simply unzip the file to a known location, e.g. your downloads folder, then open the file with LTspice. For more help with LTSpice visit this page.