Working with an integrated circuit using the example of the 555 timer IC
If you work with discrete electronic components, you can deduce the circuit based on their known electrical properties.
In this example, an LED is controlled by a transistor.
The currents and voltages in the circuit can be calculated directly using formulas.
The calculation is based on the following values, for example:
- voltage drop across the LED = 2 volts,
- current through the LED = 10 milliamperes,
- voltage drop across the transistor base-emitter path = 0.7 volts,
- voltage drop across the transistor collector-emitter path = ~ 0.1 volts, etc.
The connections are visible; if the circuit is not too complex, you have an overview and understand what is happening where.
It is different with integrated circuits (ICs) ...
... which contain a large number of discrete components such as transistors, resistors or diodes.
Here, the relationships are not visible.
You only have a housing from which connections (pins) lead:
Which pin stands for what and what it is used for can be seen from the IC's data sheet.
This means that you have to learn how each IC behaves electrically and cannot draw any direct conclusions because the internal circuit is unknown or too complex („blackbox“).
If you have a block diagram of the integrated circuit, you can deduce what happens in the IC, which is helpful.
The 555 timer IC for example contains, among other things, a voltage divider, two comparators, a flip-flop and an output stage:
en.wikipedia.org
To understand how the 555 timer IC basically works ...
... it is helpful to explore it without additional external circuitry (which determines its function).
This works particularly well with a circuit simulation program where an electronic circuit can be virtually constructed and modified.
All electrical values can be measured and optimized. You then see immediately whether the circuit works as intended or not.
Here the 555 timer IC is shown in
NI Multisim.
Its eight pins are labelled, but we will only focus on those that are required for its basic function.
In order for the IC to work, it needs a DC supply, which can be seen on the left in the picture and is 9 volts.
The IC is controlled with voltages via the "Threshold" and "Trigger" inputs.
The conditions for these inputs can be seen on the right.
The reason for these conditions is the internal circuit of the 555 timer IC, which cannot be seen here. So we take the IC as it is.
In this state, switch S1 is open, so no current flows through the 555 timer IC, it does not work.
Now we close the switch.
We see that a test lamp (right above, indicating HIGH) lights up at the output of the 555 timer IC and the voltage at the output is 9 volts.
Why this is the case is clear from the conditions on the right.
The voltage at the trigger input is 0 volts and is therefore less than 1/3 ( = 3 volts) of the operating voltage of 9 volts.
The 555 timer IC then switches its output to the level of the operating voltage, i.e. 9 volts.
Now we raise the voltage at the threshold input from 0 volts to 6.5 volts.
This causes the output voltage to drop from 9 volts to 0 volts and the test lamp no longer lights up (indicating LOW).
Here too, the conditions on the right indicate why this is the case.
Since the voltage at the threshold input is 6.5 volts, which is greater than 2/3 of the operating voltage (= 6 volts), the 555 timer IC switches its output to 0 volts.
Now we reduce the input voltage at the threshold input from 6.5 volts to 2 volts and see that the output voltage goes back to 9 volts (HIGH).
The condition on the right is that the output voltage is only 0 volts if the input voltage at the threshold input is above 2/3 of the operating voltage.
And since the current 2 volts are below 2/3 of the operating voltage, i.e. 6 volts, this is not enough to set the output to 0 volts.
Once you have understood this basic operation of the 555 timer IC, you can explore its remaining connections and then look at ways of connecting it to external components.
This way you can build timer circuits, oscillators or even a Schmitt trigger, as we saw above.
I realize that circuit diagrams, numbers, formulas and conditions are not everyone's cup of tea.
Just as my attempt to explain the basic function of a 555 timer IC might be too simple for others
But everything here follows rules and principles that can be learned. Even if it looks confusing at first glance.
I can therefore recommend working with electronics, no matter what level, to anyone who enjoys finding out connections, understanding processes and doing a bit of math.
And I hope it will help to understand the electronics in cameras a little better
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All information provided without guarantee and use at your own risk.
