Hi. I'm John P. Neumann...
In Ms. Katzens 3rd grade classroom during the holiday party we made an electronic circuit! Well, we tried to. Unfortunately, the project was overly ambitious for the time constraints that we had. So what happens next?
My child is missing parts or I don't know if they're missing parts
Understood. Not everyone got to finish. Please reach out to me at john.p.neumann [at] gmail.com and I'll be happy to drop the missing parts off. If your childs circuit is incomplete, they're missing parts. If it just doesn't work, they probably have everything, but the circuit just needs to be troubleshot.
My child didn't get to finish
I know and I feel bad about that. However, I've written a step-by-step guide below! And if you have any questions, you can reach out to me directly. If you're missing parts, see the previous section.
My childs circuit isn't working
So, this is a bit different. Some of the circuits only light up, while others blink. However, what I'm happy to do is if you can take a picture of the circuit, I'll help diagnose what the issue happens to be. 9 times out of 10, there's one thing out of place and it's super simple. Email me pictures at john.p.neumann [at] gmail.com, and I'm happy to look. If you would rather stop by, let me know and we can schedule a time for me to take a gander.
So what was this project
So the intent of the project was to create a blinking LED using a common circuit (with a few tweaks) to run off of two cr2032 batteries. The circuit is known as an "Astable Multivibrator". It's one of the most common circuits used in electronics. It generates a square wave signal and is useful for anything that requires timed pulses. In this case we wanted to generate a pulse that would turn two LEDs on and off, with neither of them being on at the same time.
Blinkin' Xmas
Blinkin' Xmas is a beginner level circuit that's formally known as an Astable Multivibrator. In simple terms, the circuit does not have a stable state and as such, continues to flip-flop between each side which provides enough power to light one LED at a time. This is an oversimplification of what it does. Think of it like this:
You have 1 power cord to charge something. But you have a friend over who also has the same thing that needs the same power cord. You decide to share the power, but only until each device is charged enough to turn on. So you plug your thing in. It turns on and your friend takes it from your device and plugs theirs in. As theirs turns on, yours turns off, so you take it back and plug yours in. This goes on until you decide that this is probably not nearly as fun as doing something else. Soooooo....
Let's build a circuit!
Breaking down the circuit
So each part does something different. Let's break down the circuit, piece by piece and talk about what each thing in this circuit is doing. Also, it's probably time to note that there is a single subtle difference between this circuit and a normal Astable Multivibrator. That difference is the addition of a variable resistor. We'll talk about why this is added in a moment. Let's dive in.
Schematic
What is this craziness above? That's a circuit. The circuit is the basis of every electronic device you've ever touched, seen, or used. The circuit describes the components (parts) and how they are all connected together. Each symbol is referring to a specific part, which has been standardized. This means that you can speak any language in the world and if you see a circuit schematic, you'll be able to read it [1]! So let's do a quick walkthrough of this circuit.
Let's start with where we're getting our power from. We see that the positive power connects to a switch. That's a double-pole double-throw switch and we're only using one side of the switch, so that means, we're treating it as a single-pole single-throw switch. Coming out from the switch, we're connecting pin 2 to both of the leds, and the variable resistor. If we go back to the leds, we can walk down the leds to see that there's a resistor connected to the cathode side of the led. After that, it connects to the collecter of the NPN transistor, which is also connected to the positive side of an electrolytic capacitor. The negative side of the electrolytic capacitor is attached to the base of the opposite NPN transistor, which is also connected to another resistor. The bottoms of those resistors are connected together, which is then running into the second pin of the variable resistor. The emitter pin of the NPN transistors are just connected to ground. SO EASY RIGHT!
If you skipped all of that, I don't blame you. That's a mouthful that doesn't really explain anything. Let's actually step through this in a sane way.
Assembly Instructions
So let's do one thing real quick, because it'll make things easier. Let's swap out that switch we have so that it's a little less confusing.
Much better. Ok. So let's not start where we did the first time: And let's get some components on the board before we add power. For future reference, this is always a good idea. Power is usually the last thing you'll add, unless you're testing a particular part of the circuit. Let's start by opening the box.
Now if we empty the box, and separate the components we've got this:
Neat! Let's take one of those things with 3 pins and looks like a fork and plug it into the breadboard. Let's start by making sure that the potentiometer (the big thing that you can turn thats on the corner of the breadboard) is to your right side (which also means it should be further away from you).
Before you plug this fork looking thing in, let's define what it is. This is an NPN Transistor. There are several types of transistors and they all do different things for different purposes. In this case, we want it to act like a gate for voltage. So the key with the transistor is that you want to make sure of three things here:
- That they both face the same direction;
- the rounded side should be facing towards the potentiometer so the flat side should be towards you;
- That when you place it, you're placing it as far to the edge of the breadboard as possible;
- That the far left pin (as you're looking at the breadboard and the potentiometer) of the transistor is in the same row as the black wire.
The reason we want the far left pin on the flat side to connect to ground is because we need the voltage to be higher on the base (the middle pin) than the emitter (the far left pin) for it to power up. So connecting to ground, is what we want. Ground, in this case, is going to be the negative side of the battery. In any case, we want it to connect to the black wire.
Once you've done that, we're gonna do the same exact thing on the other side of the board.
Again, we want the far left side to connect to ground and we want both of the transistors to face the same direction (so if the round sides are facing each other, something is wrong in the circuit).
Next, we're gonna add both of the 10k Ohm transistors. You can tell that the transistors are 10k Ohm by the colors of the bands around the resistor. In this case we want the following colors:
- Brown
- Black
- Orange
- Gold
Resistors have color codes that mean specific things. It's not something you'll memorize, but here's a way to check what the colors mean: 4 Band Resistor Color Code Calculator.
So the thing here is that the resistor has two ends. It doesn't matter which end is placed where. So, you want one side of the resistor to be placed directly next to the right-most pin of the transistor (so opposite of where you were looking last time), and the other side of the resistor should line up in the same row as the purple wire that's running to the potentiometer. The image below, should show you want I'm talking about.
Cool, so, we've now got our resistors in. Resistors do exactly what their name says: They resist! (Viva La Resistance!) What they resist is current the flows through the circuit. Resistors are part of almost every circuit and every piece of electronics that you'll ever use or build. So, you need to do the same thing on both sides again here. (You'll notice that almost everything we do on one side, we're going to do the same exact thing on the other side.)
Sweet! Nice job! Now the next thing we're gonna do is we're gonna grab those things that look like a can. Now, these are called capacitors and because they're a special type of capacitor (called electrolytic capacitors), how you place them makes a HUGE difference. So, pay attention closely to this section.
Electrolytic capacitors are polarized, which means they have a positive and a negative side. You can think of them like a battery. Every battery has a positive side, and a negative side. Or you can think of them as Two-Face. Two-Face has a good side and a bad side. The good side (the positive side) needs positive current. The bad side (the negative side) needs negative current. The easiest way to determine which side is the positive side and which is the negative, is to look for the white or grey line on the capacitor. The side with the white or grey line is the negative side. The positive side is... Yeap! The other side. So we need to connect this in a very paricular way. We want the positive side to be in front of the first pin of the transistor and the negative side of the capacitor to be in front of the 10k resistor we just added.
The image here is not great, but here's the thing, if you look at where the 10k resistor is connecting both pins, you can clearly see that we don't the negative side to be in front of the side where we connected the resistor to the purple wire. We want it to be on the same row where the purple wire is making an X. If that's not clear enough, don't forget to check the fritzing diagram so you can see where things are.
And again, do the same thing on the other side. :)
Ok, so now we've got the capacitors in. Woot! We've only got a few more things to connect until we get some Blinkin' Xmas lights!
So the next thing we're gonna do is we're gonna add the 220 Ohm resistor. This resistor has the following color code:
- Red
- Red
- Brown
- Gold
You'll be connecting this resistor in front of the positive side of the capacitor (pick one, it doesn't matter which) to the hole right before the red wire that's coming from the potentiometer (or the switch - again, this depends on the side you're doing it on).
Now we're going to add the red led. If you're not sure which is the red led (because they both are clear LEDs - poor choice on my part), take the longer pin (the anode) of the LED and put it on the positive side of the CR2032 battery and the shorter side (the cathode) on the negative side of the battery. You should not do this for longer than a second as it could damage the LED. Once you've figured that out, you want to place the LED as close to the middle of the breadboard as possible. You want the shorter side (the cathode) to be in front of the resistor you just put in, and the longer side (the anode) to be in front of the red wire coming from the potentiometer (or the switch... Yes, I'm repeating myself. Consider this verbose logging - One person got that joke... HI!).
And now... We're gonna do the same thing on the other side for the last two parts, except that this time your resistor is going to have the following colors:
- Brown
- Green
- Brown
- Gold
Again, we want the resistor to go from the positive side of the capacitor to right before the red wire that's either coming from the potentiometer (or from the switch). Then you'll connect up the green LED. The thing with LEDs is that not all LEDs are created equal. Each LED requires specific voltage to be dissipated from it so that it doesn't burn up. This is the reason that we have different resistors for each LED. This is part of what's called ohm's law. It's like when you're told to clean your room and you don't and you get in trouble. It's a law... You can't break it.
OMG! We're almost there! Alright, so two last things here. First one.
Put the switch into place. Fair warning - The switches do not sit nicely. I apologize. However, there's a hacky way you can make this work without the switch that we'll get to later. An alternative is to get a different switch (I've yet to find a switch that sits nicely in a breadboard (without mangling or soldering, so if you or your parent knows of one, please let me know). Ok, so switch is in and you're feeling awesome. The switch should be as close to the edge of the board as possible, specifically because this is a space constrained design AND because the wires have been run specifically to work the way they do. Make sure that the switch is in the off position (so to the right) so that you can experience the gloriousness of turning it on.
We're almost there. Last part. Take the two CR2032 batteries and insert them into the battery holder. Now, you're going to take the battery holder which has two pins:
- The side that has the square "nub" coming out is positive.
- The other side is the negative side.
Now, you want to place the POSITIVE at the EDGE of the board right before the long red wire is. In other words: If you're looking at the board and the potentiometer is to your right - the long red wire is in the second hole over and the second hole up. The positive side of the battery holder should be in the second hole over and the first hole. The negative side should be on the other side of the board in the same row as the positive side (so all of the black wires should be in the same row as the negative lead).
You did it! You're awesome! Congratulations! Now you can put it in your box and you've got your very own nightlight that YOU made. Or you've just got an awesome light. No matter what you made it! Move over Tesla... I've got some kids that are awesome. ;)
Parts List
Here are the various parts that we used for this. As a note, the switch should be a single pole switch, however, I had DPDT switches on hand.
Additionally, the wire at the end is only needed if you either:
- Don't have any; or
- Don't want to connect the components to each other directly.
- Yes, you can connect all of the components directly to each other. However, it's ugly and is harder on your hands.
- The latter part of the above is why using the wire is better with kids.
Resources
Below you'll find further resources for yourself or your child, as well as, downloads for the files that were created to create this project. All of the software used is "free". Eagle is an Autodesk product, but can be used for educational or hobbyist use for free with an Autodesk account. Fritzing is an open source project that has no strings attached.
I'll add the eagle file soon.
I'll add the fritzing file soon.