Break in the workshop, focus on electronics

The insides of op-amps are marvels of analog electronics design. That design, by assuring precision amplification, linearity, high speed, and so on, means that the user doesn't really have to worry much about the internals or properties of a specific op-amp. In the vast majority of op-amp circuits, the op-amp is a high-gain amplifier of any differential voltage between its + and - inputs, and is controlled by a feedback circuit. What that means is that the op-amp will drive its output voltage to make the input voltages equal. Thus, to understand the behavior of an op-amp circuit, you don't look at the op-amp, you look at the components in the feedback network.

This page shows a more or less understandable version of how to understand two simple op amp circuit topologies where the feedback is controlled through a voltage divider (pair of resistors): https://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/divided-feedback/
You will see feedback topologies like this over and over (also with capacitors if working with AC signals). IMO this is more of what an op-amp novice needs to know than the electronicshub link. I believe the treatment of op-amps in Horowitz and Hill's "Art of Electronics" is also very good.

I am currently going through the basic circuits with the operational amplifier.

Here is the inverting amplifier with negative feedback simulated with NI Multisim.

The output voltage can be set using the two resistors in the circuit.

A maximum output voltage of around 1 V below the operating voltage is possible.

Here I learned that the lower the input voltage, the greater the deviation from the calculation using the formula.

The reason for this will be interference voltages, which are noticeable here.

This can be relevant, for example, for amplifying weak exposure measurement signals in cameras, where circuits are then needed to compensate for this.

Here the operational amplifier is working as a comparator.

The task of this circuit is to compare two voltages.

One of these voltages is the reference, the other the voltage for comparison.


The reference voltage can be seen at the top left and is 2.498 volts.

The comparison voltage is shown below and is 2.398 volts, so it is smaller.

In this case, the comparator produces a positive output voltage, which can be seen at the top right. It is +4.118 volts.

The green LED lights up.




Here the comparison voltage is greater than the reference voltage.

The comparator now outputs a negative voltage.

The red LED lights up.

---

In this way, a logical operation can be carried out:

"If voltage A is smaller than the reference voltage, action GREEN occurs. If voltage A is greater, action RED occurs."

In a camera circuit, for example, the built-in flash could be activated if the subject brightness falls below a certain reference voltage value.

Or an overexposure warning could be activated in the viewfinder if the subject brightness (as voltage value above the reference voltage value) exceeds the smallest aperture and shortest shutter speed.

---

Of course, this circuit only shows the basic principle and camera circuits are much more complex.

But it is another building block to understand more.

And if an operational amplifier is shown in a camera circuit diagram, it can be checked for its function. Maybe it is switched as a comparator.


+++

All information provided without guarantee and use at your own risk.

Nice exercises; I've always found such simulations to be very informative and they're quicker to set up than a physical circuit.

koraks said:

Nice exercises; I've always found such simulations to be very informative and they're quicker to set up than a physical circuit.

Click to expand...

In the simulation you can change the values of the components, expand or reduce the circuit and always have everything in view.

With the virtual measuring and display devices you can work as you like and nothing will break.

An indispensable aid for learning and designing circuits.

Professional programs, such as NI Multisim here, also work with the dimensions of real components, errors can be built into the simulation,
the ambient temperature can be set, etc. This all comes very close to real conditions.

Indeed, some of the simulation models are pretty realistic. In most cases, it's perfectly feasible to run a simulation that's accurate enough to predict the real-world behavior of a circuit and troubleshoot it even before any parts are ordered. I virtually always simulate parts of circuits I build to verify I've got it right, there's no unanticipated effect etc.

The last application of an operational amplifier I would like to introduce here is the Schmitt trigger.

As with the previous example, this is a comparator that compares two voltages.

Depending on the result, the output voltage is either positive or negative.

Here, even the smallest voltage differences are sufficient to switch.

If the reference voltage is 5 volts and the comparison voltage is 5.01 volts, for example, the comparator switches the output voltage.
This allows an exact changeover point to be set, but this is not always advantageous.

If the comparison voltage fluctuates around the changeover point, the comparator switches constantly. Eg. 5.3, 4.7, 5.6 volts etc.
This would mean, for example, that a connected LED is constantly flashing. Or the display lighting in the viewfinder of a camera, which
reacts to changes in the brightness of the environment.

To avoid this the Schmitt trigger expands the comparator with what is known as positive feedback, which creates two changeover points that are separated in terms of voltage.

For example, the LED could be switched on at 5 volts but only switched off at 3 volts. Voltage changes between these values do not affect this; the LED does not flash.

---

The Schmitt trigger was invented by American scientist Otto H. Schmitt in 1934 while he was a graduate student.

Click to expand...

The Schmitt trigger can be constructed from individual components such as transistors and resistors or mainly with an operational amplifier.

It is an ingenious circuit based on the principle of voltage dividers and positive feedback.


In this example, the LED on the right is switched off at a reference voltage of 8.1 volts (DC voltage source, see bottom left).

By returning the output voltage to the reference voltage (see positive feedback via resistor R9), the lower changeover point (UL) for switching on the LED is formed, which is approximately 5.4 volts here.



When the reference voltage is reduced to 5.39 volts, the LED switches on again.

At the same time, the upper changeover point (UH) is set at approx. 8.1 volts using the same positive feedback principle.

The two changeover points can be set using resistors R4, R5 and R9. They can either be further or closer together in terms of voltage, depending on what you want.

---

To build a Schmitt trigger with an operational amplifier, you don't need to understand the theory behind it and the interplay of the voltages.

You can use an electronics app, for example, that shows the circuit and calculates the values for the changeover points.

The corresponding formulas are also given in case you want to calculate the values for the circuit yourself.






I recreated this circuit in NI Multisim (see above).

My values are slightly different, but that probably has something to do with the OP 741 I used. The app shows a generic operational amplifier.

---

With these considerations of the operational amplifier as an important component of analog electronics, we move on to digital electronics.

Here are just a few principles to understand how the world of high and low, or 1 and 0, basically works.

This should help when looking at complex circuits so that you don't sit there completely helpless


+++

All information provided without guarantee and use at your own risk.

A Schmitt trigger can also be built using the 555 timer IC.

The 555 IC contains, among other things, a voltage divider, comparators, a flip-flop and an output stage.

This module can be used to build timers, pulse generators or oscillators using additional external components.

The 555 IC contains 25 transistors, two diodes and 15 resistors.

See



In the following circuit as a Schmitt trigger, the 555 IC controls two LEDs.



At an input voltage of 6 volts the red LED lights up.




If the input voltage drops to 3 volts, the green LED lights up.

This creates two separate switching thresholds. The corresponding voltage difference is called "hysteresis".

For details of the circuit, see:

---

I have already seen a 555 IC in the circuit diagram of an SLR, but I can't remember which one it was.

Andreas Thaler said:

This creates two separate switching thresholds. The corresponding voltage difference is called "hysteresis".

Click to expand...

Which for a Schmitt trigger is quite essential, and one of the main reasons why they're generally not implemented with an opamp. The usual solution is to use a dedicated Schmitt trigger IC. They're not very commonly used today as discrete parts since they're integrated on the GPIO's of microcontroller as well as the digital inputs on a plethora of IC's.

Andreas Thaler said:

I have already seen a 555 IC in the circuit diagram of an SLR, but I can't remember which one it was.

Click to expand...

There are different types of 555's, but the difference doesn't mean that one is used as a Schmitt trigger, an oscillator, flip-flop etc. The difference is usually in voltage rating and power consumption, not to mention package size. The application is determined by how it's implemented. So just by noting there's a 555 in there, you can't already say what it's used for. You have to look at the context for that.

koraks said:

So just by noting there's a 555 in there, you can't already say what it's used for. You have to look at the context for that.

Click to expand...

And that doesn't include the ones that were produced back then.

Do you think that I have not addressed the topic of „wiring“ clearly enough here?

An easy-to-understand description of the 555 timer IC can be found on the website of the German electronics retailer Conrad. It is worth translating the page from German if necessary:

Andreas Thaler said:

An easy-to-understand description of the 555 timer IC can be found on the website of the German electronics retailer Conrad. It is worth translating the page from German if necessary:

NE555 Schaltungen » Aufbau und Funktionsweise des Timers erklärt

Interessante Infos zum Timer NE555✓ Interner Aufbau, Anschluss und Funktionsweise✓ Technische Daten und unterschiedliche NE555 Schaltungen✓

www.conrad.at

Click to expand...

And here (Conrad site, German) is an equally easy-to-understand article on how an operational amplifier works, using the LM358 as an example:

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:





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


+++

All information provided without guarantee and use at your own risk.

Andreas Thaler said:

In this example, an LED is controlled by a transistor.

Click to expand...

If you leave out the transistor and R2, the circuit will do the same.

koraks said:

If you leave out the transistor and R2, the circuit will do the same.

Click to expand...

What am I trying to do with this example?

To show that a discrete circuit with a few components is easy to understand and the voltages and currents are understandable as long as the circuit is not too complex. In contrast to an IC. Whether the circuit makes sense or not is irrelevant.

I also want to post articles about electronics here that might inspire others to get involved with the topic as well. In order to understand more about the electronics in cameras.

Perhaps you would like to join in, since you are an expert.

There are several publications about the 555 timer IC, I particularly like this Kindle book by Jacques Vrey:

This book is a basic electronics course guide in which you will learn some basic principles of electronics and circuit building. The book contains practical electronic exercises in which you build your own working circuits based on the 555 timer integrated circuit. While building the circuits you will also learn the fundamentals of electronics and electronic components. You will, however, need to purchase a handful of electronic components from your local electronic component store to be able to complete all the exercises. The goal of this book is to teach you the basics of electronics without being bogged down by too much theory.

Click to expand...

amazon.com


Of course, there are also numerous pages on the web about the 555 timer IC with information and circuits to recreate.

Andreas Thaler said:

I also want to post articles about electronics here that might inspire others to get involved with the topic as well. In order to understand more about the electronics in cameras.

Perhaps you would like to join in, since you are an expert.

Click to expand...

If you like these sorts of puzzles, you'll find that there are several online forums dedicated to this sort of thing. People come there and ask their questions/present their problems. Trying to figure out their problem is a nice way to learn a thing or two, I find. Not saying that we shouldn't discuss this here on Photrio. By all means, go ahead! Just offering an additional option.

Andreas Thaler said:

a discrete circuit with a few components is easy to understand and the voltages and currents are understandable as long as the circuit is not too complex. In contrast to an IC.

Click to expand...

Well, that condition expressed in "as long as the circuit is not too complex" needs to be emphasized. Generally when trying to understand an IC-based circuit, you divide it into manageable chunks that are still relatively easy to understand. Large circuits with IC's tend to be much more intuitive and easy to understand than large circuits based on discrete components. Here's an example I posted some weeks ago: https://tinker.koraks.nl/photography/solid-as-a-rock-fixing-an-old-ac-stabilizer/ The only IC's in this circuit were two opamps and a linear regulator; all the rest was done with discrete components. Had this been done the way we'd generally do it today, i.e. with a small microcontroller, analyzing the circuit would have been far easier. The circuit also would not have failed in the way it did, since the switching logic wouldn't have depended as strongly on the tolerances of aging components. The fact that we don't necessarily understand what goes on inside the IC is generally not so relevant from a practical viewpoint. We only need to have a functional understanding of it in order to work with it. Translating this to a typical 555 circuit: if you encounter a circuit that does a bit of timing or pulse generation, it would take me hours and hours of research to figure it out if it's built from discrete components. If it uses a 555, the black box behavior is in fact an advantage, since it hides the underlying complexity and we only need to bother with the visible bits, accepting the 555's as a functional building block whose implementation we don't need to be concerned with.

koraks said:

Not saying that we shouldn't discuss this here on Photrio. By all means, go ahead! Just offering an additional option.

Click to expand...

Sure, I will put the basics of digital electronics into one more article so that 0 and 1 don't remain a mystery. But that is very dry stuff and requires a special way of thinking

It's best to look at the three basic logic gates AND, OR and NOT and what you can do with them.

I can't say anything about the camera circuits in practice anyway, but the point is to at least get a little idea of what they mean.

Then we'll move again on to the screwdriver.

Finally, here is an example of how you can use the 555 timer IC as a time-controlled switch.


Monostable flip-flop (source: Jacques Vrey: The 555 Timer – Basic electronics introductory course)


The 555 timer IC cannot do anything on its own; it must be connected to electronic components and voltage.

The idea in this circuit is to make the LED at the bottom right light up for around five seconds by pressing a switch once. After that, it should go out again.


Trigger and threshold work together

If you press the switch (S1) that is connected to the trigger pin of the 555 timer IC, it is set from 9 volts to 0 volts and the IC activates its output. Current flows and the connected LED lights up.

At the same time, the electrolytic capacitor (C1) connected to the threshold pin is charged, which takes a certain amount of time. As soon as the voltage on the capacitor has reached a certain level, the 555 timer IC switches off its output and the LED goes out.


Capacitor and resistor regulate the lighting duration

The duration of the charging process depends on the capacity of the capacitor and the amount of current that flows into it per second. The amount of current is regulated by a resistor (here R1). A capacitor with a larger capacity takes longer to charge than a capacitor with a smaller capacity.

So by connecting the 555 timer IC to additional electronic components, you can create a so-called monostable flip-flop that allows current to flow for a certain time. In our example, this is through an LED.

Below the circuit diagram you can see time/voltage curves for the trigger pin (red), the threshold pin (green) and the output (blue). They show what happens when the switch on the left (S1) is activated.


+++

All information provided without guarantee and use at your own risk.

This concludes my foray into electronics.

Perhaps this information will help you get an idea of what an operational amplifier and a 555 timer IC can be used for.

As far as I remember, operational amplifiers can be seen in the circuit diagram for the Canon AE-1. Here, they are part of an integrated circuit.

And I still can't find out in which camera I saw a 555 timer IC

Andreas Thaler said:

And I still can't find out in which camera I saw a 555 timer IC

Click to expand...

Maybe it was custom to print fake type descriptions on the ICs in these earlier times already as it is custom today?

forest bagger said:

Maybe it was custom to print fake type descriptions on the ICs in these earlier times already as it is custom today?

Click to expand...

Then you can't trust the circuit diagrams from back then at all

I don't know that these will be of value when repairing film cameras, but the market for more advanced STEM toys seems to have crashed and burned, and maybe as a result, I've found 2-3 Arduino kits, plus the Kano Pixel, at my local thrift store in recent months.

Too bad about Kano Pixel in particular, as their original, cloud-based development system looked very cool, and in lieu of that, it seemed that my Pixel had been reduced to a pretty bit of useless junk. Until I found a howto for replacing the original firmware with one based on MicroPython.

But, typical modern experimenter's set is almost entirely focused the world of code, microcontrollers, and GPIO. Which isn't necessarily a bad thing, but maybe a bit too modern to relate to cameras designed decades ago!

4season said:

the market for more advanced STEM toys seems to have crashed and burned

Click to expand...

Not so sure about that. I think the main "problem" is that the ecosystem is so vast by now and there's such a massive choice in kits, modules and boards at phenomenally low prices, that it's only logical that they start heaping up all over the place. For instance, the collection of modules in the upper right section of your photo are generic parts that can be had for <$1 a piece now (SR04 ultrasonic sensor, DHT11 temp/RH sensor, 'joystick' module, breadboard 'power supply').

The interest in this subject matter is very, very much alive, also in education. The main effect this has had is that Chinese industry and retail have jumped on it, and this now puts lots of fun, useful and interesting technology in the hands of just about anyone. What you perceive as 'crashed and burned' is in fact the global democratizing of microcontroller electronics. It's unprecedented in that it manages to reach vastly more people than back in the day with HAM radio kits etc.