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This is a standard application circuit of the 555 timer, producing a pulse train of constant "low" time and variable "high" time.

It is easy to wire it up in a corner of the breadboard, but I needed a module I could plug into the breadboard. Since the circuit was so simple, I decided to make it an experiment with Surface Mount Device (SMD) techniques.

A defunct hard disk drive yielded up the necessary components. A standard 555 8-pin DIP was pressed into service. Pins 4 & 8 and 2 & 7 are connected together with wire. Islands of copper were cut on a small piece of copper clad board and components soldered in. A jumper selects between capacitors of 10, 1 and 0.1 microfarads, or none at all. Plug-in sockets for connection to the outside world are individual pins extracted from a turned pin IC socket. As a simple circuit, it made a nice introduction to the world of SMDs.

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