Practical Electronics/Plugins/Astable

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.

555 Mk-sp Diagram.svg

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

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.

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


Enable pinEdit

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.