1993 NE555

On the year 1993, most of the time was spent going through different transistor circuits diagrams, inspecting broken electronic equipments etc ... This was a hobby. Had a vague idea on how transistor was biased. But didn't knew the exact reason for using various component values (like resistors and capacitors) on the circuits. The exact theory behind designing the component values got to me only much later. Also didn't know the relevance of different models of transistors were used. Didn't even knew there existed something like datasheets for these transistors.

I had couple of ITI text books on radios and amplifier circuits with me. Also, there was one book on old valve radio designs. Had a handbook of various types of transistor radio circuit schematics. A lot of time was spent on these books understanding audio amplifier circuits. It was a little bit confusing that most these books had circuits with PNP transistors, but most of circuit boards I had was of NPN transistors.

Lot of circuits were assembled and experimented. Design, assemble, experiment and dismantle, this was a constantly repeating sequence at that time. The LED dancing lights circuit with BC547 was an example. Important thing about circuit design is that, you should know deep enough of about the schematic that, you should be able to predict how your design will function even before it is powered on. Without this visualization it will be difficult to make successful designs. The same visualization is required is required to fix a broken equipment as well. You should be able to envision how the circuit will work on real world. This will also help you to locate the parts of the circuit which are not functioning as expected.

2 LED Dancing Lights

3 LED Dancing Lights

5 LED Dancing Lights

Also built few transistor audio amplifier circuits and tried tweaking them. The only tools that was available was soldering iron, screw driver and an earphone. For most of the basic things these were enough. Most of the tools were not that expensive compared to today. For example, the soldering iron costed me 25 rupees and resistors used to cost 20 paise per piece.

Most of the circuits were assembled on common PCB boards. Great deal of efforts were spent on manually routing the circuit on these boards. Many years later this helped when designing actual PCBs on CAD software.

Sometime this year, my friend Edwin shared with me some teaching notes on NE555. His mother was a teacher and at her school during the summer vacation there were some classes organized on electronics. The teaching notes also contained a huge cache of circuit schematics of NE555 on various operating modes. It even explained details on relevance of different IC pins and how they need to be biased for putting the IC in to different configurations. This was the first time something more in line like a datasheet was available to me and NE555 configurations were relatively simple compared to the transistors. More over this IC was quite cheaper to procure. The IC packaging was compact and simple enough to be used on small circuits.

The NE555 can be used in different operating modes. Functionally, few popular ones were as an oscillator and as a timer. We used this IC on LED flasher circuits and sound tone generator circuits.

2 LED NE555 Astable Multivibrator

NE555 Tone Generator / Piano

Later this year, again started focusing on radio and amplifier designs. Lot of time was spent on actual design concepts from valve vacuum tube circuits. This later helped on understanding how the upgraded transistor designs work for the similar functionality. Considering the books I was referring were quite old, it gave an insight of why exactly they chose particular design patterns on different sections of the circuit.