So here I am, staring at bookshelf, thinking on what to read. While going through I found my old school note book where I had notes about creating electronic circuits. One of my favorite one is 555. Later that afternoon going through some shoe boxes, I found electronic components that were sitting there since long time. The moment I open the shoe box they started screaming at me: Solder me!, let me achieve the purpose in my life as a component. Get me wired and jolt me. I could not ignore their dramatic pleas to get burned with hot melting lead.

I quickly found one 555 chip and other components that could be assembled in an astable multivibrator. Lot of information related to IC chip 555 is available on web so, I will keep the description short.

An astable circuit produces a 'square wave', this is a digital waveform with sharp transitions between low (0V) and high (+Vs). This little circuit has many applications. Inner working of chip 555 and their application can be found on the web.

The time period (T) of the square wave is the time for one complete cycle, but it is usually better to consider frequency (f) which is the number of cycles per second.

T = 0.7 × (R1 + 2R2) × C1
f = 1.4 (R1 + 2R2) × C1

T = time period in seconds (s)
f = frequency in hertz (Hz)
R1 = resistance in ohms
R2 = resistance in ohms
C1 = capacitance in farads (F)

The time period can be split into two parts: T = Tm + Ts
Mark time (output high): Tm = 0.7 × (R1 + R2) × C1
Space time (output low): Ts = 0.7 × R2 × C1

Many circuits require Tm and Ts to be almost equal; this is achieved if R2 is much larger than R1.

So, here I am at my soldering station and I was able to assemble an astable mutivibrator in 20 mins. Please see the pictures.

It is nice feeling to work with real components after working with software components so long. There are significant similarities between hardware components and software components. Have long experience with software components and enough experience with hardware components I am able to draw similarities in their working, design, reliability, features, cost to manufacture, cost to support and cost & effort to use it reliably. Most importantly the assembly and manufacturing of the components. Unlike hardware product assembly lines, there no software product line that are available that can match the agility, cost & reliability of the hardware product assembly lines. This is an emerging field with lots of tools coming into market. There are many more aspects that we can compare and talk about software product line and hardware product lines. To keep this blog short I will talk about these aspects in my later blogs of software production line automation.