Practical Electronics/Plugins/Astable

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This plugin consists of a single 555 Astable. This plugin is very versatile, and can be used for any number of things, but it often is used to give a clock to run a circuit. The plugin below gives a pulse of about 2Hz with a very low mark-space ratio. The circuit diagram is given below.

This circuit obeys the following formulae with regards to its frequency and mark space ratio.

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This is different to the design equation for the standard 555 Astable. (R₂ instead of 2R₂)

The values below give a frequency of about 2Hz, with a mark-space ratio of about 1:50.

The stripboard layout is as shown below with a component list.

Ref. Component IC1 555 Timer IC R1 10K Resistor R2 330K Resistor C1 2.2μF Capacitor D1 1N4148 Signal Diode

[edit] Variations

[edit] Enable pin

To give this plugin an enable pin, replace the wire link from Pin 4 to +V with a 10K resistor going from Pin 4 to ground (Pin 1). Then add a header pin to Pin 4. A high signal on this pin will cause the astable to function, a low will disable it, locking the output low.