Break in the workshop, focus on electronics

[Andreas Thaler]

I have worked through my open repair projects in the last few months and am now taking a longer break.

During my last project I noticed that I was no longer prepared to fight for success. So it's time to put the screwdrivers down for some time.


Electronics in cameras

I would like to pursue my other area of interest, electronics, with a focus on the electronics in SLRs.

Unfortunately there is almost no specialist literature on this and documentation is also rare.

It is not enough to admire the complex electronics in SLRs, you should at least understand how they basically work.


The best place to find information on this is in The Camera Craftsman and the SPT Journal as well as the C & C Troubleshooting Guides as far as available.

Here it is usually the articles by the highly respected and brilliant Larry Lyells that provide further information.


A general approach

To keep things simple I will approach the topic in general and try to understand the respective camera circuits in terms of system and process.

Analogue and digital electronics can be found in my favourite cameras from the 1980s, and this also involves microprocessors and microcontrollers. A fascinating subject.

I look forward to reports and discussions on the topic!

 

[Andreas Thaler]

After a quick repetition of the basics of electronics, it's time to specialize.

I'm currently working on operational amplifiers, their application and wiring.

To do this, I'm building circuits from the learning kit "Introduction to electronics with operational amplifiers". There are descriptions and all the electronic components are already included.

But as with repairs, the table quickly gets full and it takes just as much concentration.

For the experiments, I do circuit calculations, which I compare with the measured values. Then I simulate the circuit in MultiSim on the PC and see if everything works together.

Operational amplifiers are high-quality integrated amplifier circuits that can be used to solve various tasks depending on the wiring, e.g. amplifying sound signals or signals from sensors, but also comparing two voltage values.

The learning kit contains the popular LM358, which integrates two operational amplifiers.

I want to use this to get myself ready to make the operational amplifier circuits in the Canon AE-1, for example, easier to understand.

 

[4season]

That's a pretty sweet experimenter's kit! Most of the ones that I've seen concentrate on Arduino, Micro Bit and Raspberry Pi, with much emphasis on coding, and not so much about analog circuits.

 

[Andreas Thaler]

That's a pretty sweet experimenter's kit! Most of the ones that I've seen concentrate on Arduino, Micro Bit and Raspberry Pi, with much emphasis on coding, and not so much about analog circuits.

I'm very interested in the basics, even if you can't build great circuits with a few discrete electronic components. But that's not my goal.

Microcontrollers are also fascinating but I have an aversion to programming, it's not my thing.

 

[Andreas Thaler]

ELV offers experimental boards for analog and digital circuits. This includes a board for the popular timer IC NE555.

This comes with connections and standard components already mounted, saving space and assembly and only requiring wiring on the board.

The experimental boards can be purchased as kits or already assembled.

ELV Bausatz Experimentier-/Steckboard EXSB1 inkl. Gehäuse

Eine Versuchsschaltung auf einem Steckboard aufzubauen ist deutlich komfortabler als das Auflöten von Bauteilen. Veränderungen in der Schaltung…

de.elv.com

ELV Bausatz Digital-Experimentierboard DEB100

Im Digital-Experimentierboard DEB100 sind bereits alle für Experimente grundsätzlich benötigten Bauteile integriert, sodass nötige Verbindungen nur…

de.elv.com

ELV Bausatz NE555-Experimentierboard NE555-EXB

Das großzügig dimensionierte und mit praktischer und hilfreicher Bedruckung versehene Experimentierboard ermöglicht das Experimentieren und die…

de.elv.com

Experimentierboards

Stöbern Sie durch unsere große Produktauswahl aus dem Bereich Elektronik-Bausätze und Experimentierboards. Jetzt im ELV Online-Shop informieren. ELV…

de.elv.com

 

[Andreas Thaler]

That's a pretty sweet experimenter's kit! Most of the ones that I've seen concentrate on Arduino, Micro Bit and Raspberry Pi, with much emphasis on coding, and not so much about analog circuits.

I have some work ahead of me

This is for practice and in-depth study, with a focus on better understanding camera electronics.

There is no literature on this, so I'll try with the basic components and basic circuits.

 

[Andreas Thaler]

You can use these learning kits however you want. You can simply recreate the circuits or think about how everything works.

It's also a good opportunity to practice calculating and measuring electrical values.

Not everything is explained in the manual in detail, so you have the opportunity to clarify questions yourself using specialist literature.

Time at the table passes quickly.

How much current flows through the LED? But is that the total current flowing through the circuit?

Modification of the circuit to better understand the connections. Here the bridging of a simple touch switch with a plug-in cable.

Approach to a current calculation by hand, calculated with a pocket calculator.

Confirm the result with the app (Electronic ToolKit PRO). The power loss at the resistor is also displayed here.

Enter the measured and calculated values into the circuit diagram, comments for explanation.

 

[4season]

You can use these learning kits however you want. You can simply recreate the circuits or think about how everything works.

Yours looks like a modernized, and more adult version of a kit that I was given when I was a kid:
https://www.hlj.com/my-kit-150-electronics-set-gak02098

But I recall mine featuring a selenium solar cell - and being able to buy a replacement from a Radio Shack store! Yes, I am feeling very old right now. Elenco still offers something similar in the USA:
https://shop.elenco.com/consumers/electronic-playground-130.html

FWIW, Gakken still offers "Science for Adults" products, but they can be a bit pricey:
https://otonanokagaku.net/english/

 

[Andreas Thaler]

And here the circuit simulated in NI Multisim:

Circuit description (without details):

• This circuit is designed to amplify a weak input signal so that the LED at the bottom right lights up.
• The sensor on the breadboard consists of two contacts that are closed with the finger.
• Skin conducts, but the resistance is very high. Therefore, only a small amount of current can flow.
• Depending on whether the skin is dry or moist or the pressure on the contacts is high or low, the "finger switch"
  conducts more or less current to the LM358N operational amplifier.
• In the simulation, I replaced the finger and its resistance with a potentiometer (R3) whose resistance can be adjusted.
• The operational amplifier is wired with negative feedback so that it amplifies the weak input signal via the finger (potentiometer)
  to provide the LED with enough current to light up.

• The potentiometer allows maximum current to pass (i.e. the finger is moist or has good contact pressure).
• The input signal of 1.19 uA is amplified and a current of 5.4 mA flows through the LED.
• This corresponds to an amplification of approximately 4500 times (!).

• Now the potentiometer reduces the current by 50%.
• This means that the input signal is amplified less and the LED lights up more dimly.

• And finally, the potentiometer is set so that only the minimum current flows into the operational amplifier.
• The amplification is too low for the LED, it just glows.

Conclusion

• The operational amplifier can be used to amplify weak currents.
• One such weak input signal in the camera can be the current from a photodiode that measures the brightness of the subject.
• An operational amplifier is used to amplify it so that an LED exposure display lights up in the viewfinder.
• But you can also use the operational amplifier to compare two signals and determine whether the signals are the same or different in strength (comparator).
  Logical circuits can be built with this.
• But I don't know enough about that and refer to the specialist literature Or maybe someone would like to say more.
• To understand what an operational amplifier is and what it can be used for, this example is enough for me.
• And by now I don't want to know much more than that, because I'm just interested in an overview of camera electronics. The danger of getting lost in the depths of electronics is huge ...

+++

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

 

[Andreas Thaler]

Yours looks like a modernized, and more adult version of a kit that I was given when I was a kid:
https://www.hlj.com/my-kit-150-electronics-set-gak02098

But I recall mine featuring a selenium solar cell - and being able to buy a replacement from a Radio Shack store! Yes, I am feeling very old right now. Elenco still offers something similar in the USA:
https://shop.elenco.com/consumers/electronic-playground-130.html

FWIW, Gakken still offers "Science for Adults" products, but they can be a bit pricey:
https://otonanokagaku.net/english/

Very tempting!

But I'm staying strong because I want to go back to the broken cameras and screwdrivers!

 

[Andreas Thaler]

The great thing about working with analogue electronics is the combination of building on the breadboard, circuit calculations, measurements, simulation, maybe soldering a prototye and bringing it all together.

This means you can spend hours working on details and always have something different to do, so there is a lot of variety. And you learn a lot in the process.

 

[Andreas Thaler]

The author of the learning package is Burkhard Kainka, one of the leading electronics engineers in Germany with a focus on imparting basic electronic knowledge, both analogue and digital.

Elektronik und Mikrocontroller

b-kainka.de

 

[Andreas Thaler]

What's interesting about the circuit simulation above is that the current through the LED is higher than the total current of the circuit. That's actually not possible.

Am I misunderstanding something or is it Multisim?

 

[Andreas Thaler]

The circuit is an impedance converter with a gain of 1. The input signal is therefore not amplified.

So why the operational amplifier?

The purpose of this circuit is to keep the input signal unchanged when there is a load.

For example, I could apply the weak output voltage of a photocell to the input of the operational amplifier and connect a load behind it, such as an LED.

Without an operational amplifier, the LED would reduce the output voltage of the photocell and receive less current, so it would not shine as brightly.

I simulated the circuit in EveryCircuit:

The picture shows three independent circuits for demonstration purposes.

Above is the circuit with the operational amplifier. On the left is an input voltage of 4.5 volts, which is output on the right at the same level as an output voltage. The load is a 1 kiloohm resistor. 4.05 milliamperes flow through the resistor. This is enough to make an LED glow dimly as a load, for example.

At the bottom right is the „photocell“, shown as a loaded voltage divider, with a load of 1 kiloohm too. It can be seen that the output voltage has dropped to 4.09 millivolts, i.e. by a factor of 1000. Only 4.09 microamperes of current flow through the resistor, 1000 times less. If the load were an LED, the current flowing through it would also be 1000 times smaller and that is not enough to make it light up.

Below on the left is the simulated photocell as an unloaded voltage divider. This structure can also be found in the circuit with the operational amplifier above. The output voltage is 4.5 volts.

Here are two more simulations with lower load:

Load = 100 ohms

Load = 10 Ohms


It can be seen that the output voltage at the operational amplifier remains the same and an increasingly larger current flows.


Conclusion

• The operational amplifier circuit as an impedance converter ensures that an input voltage remains stable, even when it is loaded.
• This is important for measuring circuits, for example.

---

https://www.allaboutcircuits.com/technical-articles/negative-impedance-converters/

 

[Andreas Thaler]

There are mathematical formulas for dimensioning the circuitry of an operational amplifier.

For my purposes, I now understand enough to be able to imagine this circuit variant.

This should help me when I see such a structure in the circuit diagram of a camera.

Maybe someone who has a deeper insight than me would like to comment

 

[4season]

What's interesting about the circuit simulation above is that the current through the LED is higher than the total current of the circuit. That's actually not possible.

Am I misunderstanding something or is it Multisim?

I'm pretty sure you can do that, but at reduced voltage. Maybe measuring VA would give you a truer sense of what's going on.

 

[Andreas Thaler]

I'm pretty sure you can do that, but at reduced voltage. Maybe measuring VA would give you a truer sense of what's going on.

But according to Kirchhoff, all partial currents must add up to the total current and this must also flow through the return conductor to the voltage source.

Definitely interesting.

 

[Andreas Thaler]

But it's the same in EveryCircuit, see circuit on top.

Here, 4.5 mA flows through the load resistor on the right, but only 2.05 uA flows back to the voltage source through the voltage divider.

How is that possible?

I must have misunderstood something central here

 

[Andreas Thaler]

The 4.5 mA are real, where do they flow?

 

[Andreas Thaler]

I measured the current through the LED via the return conductor to my laboratory power supply at 2.2 mA. So the total current does not disappear via ground. I am relieved.

The measured current differs significantly from the simulated one (4.5 mA) but that doesn't matter. The operational amplifier in EveryCircuit is a generic component, so that may be the reason. Or the forward voltage of the LED used on the board differs from the simulation. This is just about the principle.

That concludes the topic of operational amplifiers, but I will continue to look into it a bit.

I am particularly interested in the circuit as a comparator, which is also used in cameras.

 

[Andreas Thaler]

I forgot to set the LED in the simulation. Now the current matches the measurement.

 

[koraks]

Here, 4.5 mA flows through the load resistor on the right, but only 2.05 uA flows back to the voltage source through the voltage divider.

Looks like that simple simulation powers the theoretical opamp from a theoretical, implicit source. So the output of the opamp sources current that doesn't come from the 9V source you modeled. Just like in the real world; the current won't be drawn from the non-inverting input either, but it'll be supplied by the opamp's power supply rail.

The operational amplifier in EveryCircuit is a generic component

Exactly. It also will have infinite current source and sink capabilities, as well as an infinite voltage rating and it'll be perfectly rail-to-rail.

Likewise, there may be faults in the simulation model of the LM358 you used in the other simulator, resulting in weird outcomes.

I am particularly interested in the circuit as a comparator

For that, you use a reference voltage and apply it to the inverting input. Note you can make the comparator swing either way depending on whether you use the inverting or the non-inverting input for the signal.
Note also that there are dedicated comparator IC's that work largely like an opamp, but they're intended to provide a clean binary output and generally involve a hysteresis to prevent oscillation if the input is very close to the reference voltage.

 

[forest bagger]

The 4.5 mA are real, where do they flow?

It seems to me that your simulation does'nt understand what an OP amp is doing.
The current that flows out of the output of the OP amp comes directly from the + 9 V DC of the battery over the diode D1.

 

[Andreas Thaler]

It seems to me that your simulation does'nt understand what an OP amp is doing.
The current that flows out of the output of the OP amp comes directly from the + 9 V DC of the battery over the diode D1.

Circuit simulation is a great thing, complex processes can be captured in detail and in any time extension.

Even the big Multisim is not error-free, but there are users who ask questions.

 

[Andreas Thaler]

Here is a very good and understandable introduction to the topic of operational amplifiers.

The almost perfect amplification circuit in a small format that can be used to more than just amplify signals:

Operational Amplifier Basics

Here is the detailed information about operational amplifier basics, circuits, characteristics, Frequency response and applications.

www.electronicshub.org

The OP Amp 741 is the classic. It is also available as a kit with discrete components. This shows what is inside a small OP Amp IC:

The XL741 Discrete Op-Amp Kit

Evil Mad Scientist Shop: DIY and open source hardware and software for art, education, and world domination.

shop.evilmadscientist.com

IC 741 Op Amp Circuits Characteristics & Pin Diagram

A complete guide to IC 741 Op Amp circuits. Learn about why IC 741 is called operational amplifier, characteristics along with pin diagram.

www.electronicshub.org