# Schematics (understanding and drawing them)

Hey guys,

I’d like to open this thread to discuss about drawing and understanding electronic schematics, and would love if this becomes a place where newbies can share their first attempts and be corrected by those who are more experienced

As u know I’m quite new to electronics and would love to start drawing my schematics.
I got a couple of questions to start:

1. How did u start approaching schematics? Got any suggestions on how to start drawing your own?
2. Where do u all guys draw your schematics online?

Hier is the one I drew for the [Arduino controller] that I built for my sound installation. I’d love to get some feedback on this!

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I’m known to occasionally draw my schematics by hand, especially when sketching out a new design, but otherwise I mostly use EasyEDA these days. A lot of people use and like KiCad, which is a bit more powerful but it’s 2020 and I don’t install software if I don’t have to

So what is your circuit supposed to do? I see a 5 V battery (is that a thing?), two LEDs without current-limiting resistors, so they’ll die almost immediately, and two variable resistors that don’t do much, except consuming 5/5000 = 1 mA at one end, or shortening the battery and damaging themselves at the other end. That’s probably not what you set out to build

(I can guess what you’re aiming for, but explaining it to yourself in terms of your schematics might be a more useful exercise.)

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Every circuit has at least one goal and it is that which you need to concentrate on. So probably you are trying to solve a problem, like: my signal is too low in amplitude. Next you need to come up with an algorithm or plan or method how to resolve the situation. One plan could be: amplify the amplitude by multiplying it with a constant, another could be to add a constant voltage to it. After that, and I want to emphasize this, after coming up with a plan, you start the execution.

If you are new to electronics, first you need to study the laws of physics involved. What is the relationship between voltage, current, resistance etc. Then you study what type of components / tools exist. How does a diode work, what are its limitations? How does a resistor work, what are its limitations? You study example circuits, lots of them. Often from those you get inspired to make your own variations. Get familiar with what voltages are common in circuits. Is it odd that a pre-amplifier draws 1 A of current or not? Is 50 Volts a common voltage to power an amplifier in a radio or not? Oh yes, and don’t forget that electronics from a certain voltage on start to get dangerous. Invest in a multimeter or 2. Doesn’t have to be expensive, the important bit is that you do measurements, lots of them and learn from those.

The LEDs in your schematic show that you haven’t found out about the maximum voltage a LED can withstand and the maximum current they can hold, potentiometers of value 5k cross the power lines is an odd construct. Again if you look at lots of example circuits, after w awhile you would have spotted the series resistor a LED is often accompanied by and probably started to wonder why that is the case. Asking yourself that question will help you a lot.

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Are you me?​​​​​​​​​

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@fredrik thanks for the advice on the website! In fact I’d like to start drawing my schematics by hand, which I find much more fascinating.
Yeah now that I think about it my schematic doesn’t make any sense ehehe, the error is that the pot is connected to the LED, affecting its brightness. I get quite confused when it comes to drawing components that like pots have 3 pins; in this case the anode of the LED is connected to the center pin of the pot and the cathode to ground.
How should I draw something like that?

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You can draw that exactly as you just described it. But the potentiometer might not be able to withstand the current for the LED if it is a low power type for long.

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@Jos I studied already about components,Ohm’s Law and stuff and I already have a multimeter and know how to use it I also already built this circuit and I wanted to try laying down a schematic (it has been working for about a week now)! I recognize that it deosn’t make any sense ahaha.
Basically the purpose of this circuit is to act as a controller: I’m reading the two resistance values of the pots with an Arduino, and mapped them to Max/Msp to control my patch. In this case I’m using 5k pots because I found that they were fitting good to my purpose, which is moving around the screen. I also tried bigger values and I noticed that they moved too slow. Thanks for your advices

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But how do I specify wether other components are connected to the central pin rather then to the side ones? I guess that the incoming signal is connected to one of the sides, which is one connection on the schematic, but it’s the output that confuses me

The output is the bit sliding over the potentiometer (internally) from one side to the other, i.e. its middle terminal. It is in fact a voltage divider that consists of 2 resistors the ratio of which you can change by rotating the axis of the potentiometer. The confusing bit may be that both input and output share the GND as terminal.

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Yeah yeah I understand that, so I just draw it like this? I noticed also that the direction of the ramp will vary depending on which of the sides pin we plug the incoming signal right?
Is this correct now?

I got also another question regarding the connections.
I know that the dots are used to indicate that two wires are connected together, do I have to draw them also to indicate that a component is connected to that (like I did here) or only when it’s wire and wire?
(sorry I forgot to draw the arrow on the second pot, it is not a resistor!)

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What you’ve drawn is a symbol for a variable resistor, which in practice normally is a potentiometer with one end terminal connected to the middle. A potentiometer with all three terminals has one of these symbols (I guess the left is more used in America and the right more in Europe):

The resistance from the top to the bottom is fixed, and the resistance between either and the middle varies.

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To stick with your design, this is what I mean.

But this is purely for illustrative purposes because if you would connect a LED !with a series resistor! to the output of this little circuit the potentiometer would than have to be of a type that can conduct the current drawn by the LED. A “normal” potentiometer would not be able to do so. So this is not a good way to e.g. make a dimmer for a LED.

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This is something I did not know. Can you go into some detail? Of course the potentiometer alone would not be safe for the LED, because it can go down to ~0R, but if there’s a series resistor of suitable size, is there still a risk to the potentiometer?

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If you see the potentiometer as 2 resistors, then the upper half becomes smaller and smaller as you move the slider up. The power in that small resistor (I^2 * R) will produce more and more heat on a smaller surface and it will likely burn.

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So what current level is safe? When I look at a potentiometer datasheet I see a power rating but that’s presumably not for power across a tiny fraction of the pot. And I don’t see a current rating.

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That is a good question. I only consider them usable for signal manipulation, not for anything above fractions of a milli amp. For real power you would use robust devices like this:

or this:

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Sorry so should I add resistors between the pot and the LED? I don’t want the thing to break or worse burn in the middle of the installation

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The resistor is a start, but you need to make sure that the current that the led needs to light up is maybe less than 1 mA. So the series resistor should be something like (5 - 2.7) / 0.5e-3 = 4600 Ohm. Make it 4k7. I’m assuming the LED will light at 2.7 Volts (this depends on the color of the LED / the material it is made from). Try that and tell us whether it worked.

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The power rating is for the full potentiometer track, so you can calculate max current as sqrt(power/resistance). E.g. for a 10k potentiometer of the type you linked to, sqrt(0.2W/10k) = ~4.5 mA. This applies to any point of the track, so it’s safe to use as a voltage divider up to ~45 V across the entire pot (but you probably want to stay well below that and also make sure you don’t otherwise exceed the spec, e.g. sqrt(0.2W/1M)×1M = ~450 V across a 1M is probably not a good idea).

If you use the same potentiometer as a variable resistor, you must make sure that you don’t exceed that current through the circuit even with the potentiometer at ~0 ohm, e.g. by making sure that you have other resistances in series, or limited current drive capacity.

If you need to regulate current, get a rheostat, as Jos says; they’re built for that purpose.

(Or use active components; there are plenty of things that are happy to regulate currents, but tiny potentiometers aren’t such a thing )

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I think that the LEDs haven’t pop yet because I supply 5V with Arduino, and not directly from the wall socket. I tried that as well and I saw that the response on my computer was extremely scarattering and jittery, so I went back to the Arduino. Internet says that it supplies 40 mA of current

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