# Home school circuit analysis class suggestions needed

#### MrChips

Joined Oct 2, 2009
28,111
Another father who has offered to help teach is more of a software guy, I’m hoping he can teach arduino for a couple weeks.

I like the idea of using the arduino and transistor to control a light bulb. That’s a great application. Arduino has enough power for an LED, But not much more. So to get more power, let’s use a transistor!

I might need a little help putting that all together…
We are here to help. Don't be afraid to ask.

#### dl324

Joined Mar 30, 2015
15,510
so here is an NPN. If enough current flows to the base then the led turns on.
You're using the transistor as a switch. In saturation mode, we assume a beta of 10 for 2N3904. To have a 30mA LED current, you need to have at least 3mA of base current.

Many T1 and T1-3/4 LEDs will have a maximum continuous current of 20mA. You can drive them at higher currents when the duty cycle is less than 100%. Some HP LEDs from the 70's allowed peak currents of 1A.

#### rpschultz

Joined Nov 23, 2022
279
I appreciate the help!
Feels like I’m drinking from a fire hose…

#### crutschow

Joined Mar 14, 2008
31,495
So what’s the easiest type of solder for beginners? 60/40? 63/37? Flux core? Rosin core?
Make sure you always use rosin or other flux designed for electrical work, never acid flux.
Acid flux is designed for soldering two pieces of metal, such as copper tubing joints, not electrical wires.
It is corrosive to wires and leaves a conductive residue.

#### MrSoftware

Joined Oct 29, 2013
2,069
I appreciate the help!
Feels like I’m drinking from a fire hose…
Technical people tend to overcomplicate things, at the level you're teaching at keep it basic, don't let the crowd confuse you with details that don't matter at this level of design. You're a mechanical guy, so a comparable example would be teaching kids to build a bridge using popsicle sticks and glue. You might teach the basic design of a truss, "here glue the sticks like this because it's strong", but you're certainly not going to teach them how to solve all the stresses in a truss. The same thing applies here, glue some parts together and see how it works, mention the concepts but don't get lost in the itty bity details.

#### rpschultz

Joined Nov 23, 2022
279
Yup, absolutely. With transistors, I’m just trying to understand it well enough to teach the basics in a way they understand.

I also like the idea of them learning 3 ways:
On paper
In spice (Eagle)

if they get the same answers for all 3 it should reinforce the concept. Anyway, just talking out loud.

Ultimately they’ll walk away from this class with a nice solder kit and a circuit they built and hopefully the confidence to do “the next” project on their own if they want.

#### MrChips

Joined Oct 2, 2009
28,111
A word of caution.

Inevitably, students will ask a question such as, "Why do we do ___ and not ___?"
If you truly don't know the answer don't guess. Tell them you don't know and direct them to how they can find the answer on their own. Or say, "I will find the answer and get back to you."

I have witnessed instructors trying to teach a subject that they knew little about. That is very sad state of affairs.

#### rpschultz

Joined Nov 23, 2022
279
I’m not a BSer. It’s easy for me to say, “I don’t know. Let’s look for the answer together.”

#### dl324

Joined Mar 30, 2015
15,510
With transistors, I’m just trying to understand it well enough to teach the basics in a way they understand.
I'm not sure what simulator you're using to get this result:

An LED with only transistor leakage currents isn't going to have a 1.3V drop. And there aren't many red LEDs that are going to have a forward voltage drop of 1.85V at 30mA.

If you're going to use this circuit to teach, you should be prepared to explain why you chose each component value.

#### rpschultz

Joined Nov 23, 2022
279
Yeah I just found that on the internet as an example of npn transistor. Most of the circuit made sense to me. But You’re right, I thought most LEDs maxed out at 20mA. Sorry, bad example.

#### dl324

Joined Mar 30, 2015
15,510
I just found that on the internet as an example of npn transistor. Most of the circuit made sense to me. But You’re right, I thought most LEDs maxed out at 20mA. Sorry, bad example.
Have you tried to simulate with Eagle yet?

Another point. Electricial engineers/technicians don't like colored schematics. Do mechanical engineers make colored drawings?

With Eagle, you can print black and white PDF and do a screen capture for posting. That gets rid of the meaningless colors.

#### rpschultz

Joined Nov 23, 2022
279
That’s an interesting topic. Obviously drawings have always been black/white. But the drawing standard ASME Y14 allows for color. I sometimes use color for isometric views of assemblies to give better contrast. It’s an option that some engineers use occasionally.

I’m in Puerto Rico on vacation. I found out about my friends brain tumor while my family an I was at the airport. So I have limited ability right now (just a phone). But yes I have been using Eagle for a few months now. I Learned how to simulate a HPF cutoff frequency. When I get back I’ll definaty have to begin simulating transistors.

funny. @MrSoftware suggested multisim. When I visit that site here in Puerto Rico it’s all in Spanish

I’ll keep the black/white thing in mind, thanks.

#### dl324

Joined Mar 30, 2015
15,510
Multisim isn't free. I used the free version Newark or Mouser offered. They stopped supporting it, so I stopped using Multisim. Didn't like it much anyway. The only reason I used it was because it was popular with schools and a lot of students show up here using it.

I use a logic simulator quite a bit. Mostly because I'm lazy and sometimes because I don't have the parts I need (and don't want to buy them). For analog, I'm old school and enjoy the challenge of using the simulator between my ears. I use LTspice mostly for varying things (like temperature) that are too tedious with actual breadboards.

The version of Eagle that I use is very old and I don't like what they've done in the newer versions. Do they still have a free version that requires an account? They didn't add simulation support until 8.4.

#### rpschultz

Joined Nov 23, 2022
279
I’ve got Eagle 9.6 I think. It’s free so far. I really like it, but I have no reference to anything else.

#### rpschultz

Joined Nov 23, 2022
279
After only using Eagle for a month or two, I created a circuit (with help from people here), simulated it and did the layout, and sent it to Osh Park for fab. Really easy. I’ve got pictures of the layout at the end of that thread.

again I have no reference to other software. But for someone who has never done anything like that before, it was pretty easy in Eagle.

I spent a couple weeks on the schematic. Then a couple weeks on the PCB layout. I gotta say, the auto router was amazing. I ratsnested it to the best of my ability, and the auto router gave me great options. I picked the best one and just tweaked a few areas and increased trace thicknesses. Super easy.

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#### MrSoftware

Joined Oct 29, 2013
2,069
Another point. Electricial engineers/technicians don't like colored schematics. Do mechanical engineers make colored drawings?
I like color sometimes, it depends on how busy the design is and what the color signifies. Color can be helpful on a very busy page.

Multisim isn't free.
Is it only free for existing accounts? I've been using a free account for years, I just opened one of my saved designs now and it's still working. It's great for simple stuff and works in a web browser so no need to install anything.

#### rpschultz

Joined Nov 23, 2022
279
I like color sometimes, it depends on how busy the design is and what the color signifies. Color can be helpful on a very busy page.
if you just screenshot the Eagle schematic it has all those +s everywhere, grab points for each component. So I export the image(gets rid of +s), and I prefer it in color although there is a B/W option. I’m not sure why color would be bad? It distinguishes between different type of components.

#### BobaMosfet

Joined Jul 1, 2009
2,063
A friend of mine teaches a high school circuit analysis class to home schoolers. They meet once/week. 15 boys age 14-17, my 14 yr old son included. My friend (40) just got diagnosed with a brain tumor, 3 young kids. Ug. But we are hopeful, he’s still in the diagnosis stage.

I offered to teach the 2nd semester for him. I’m a mechanical engineer who has dabbled in electronics for 25 years. Guitar amps, pedals, etc. I recently designed a circuit here on AllAboutCircuits; a condenser mic preamp/HPF for my guitar. Schematic, sim and layout in Eagle. Prototype PCB being made currently at Osh Park.

First semester the kids got a lot of the basics. For the 2nd semester I’d like to shift focus and make it more hands on. I’d like to teach them to solder and by the end of the semester for them to build a circuit of their choice. They could copy a circuit they find on the internet, buy/build a kit, or design their own. The class will learn Eagle and put their circuit through Eagle Spice.

They all have an Arduino board in their packet and I should be able to acquire enough multimeters for everyone. Amazon has decent looking solder kits for $12/ea. I have a decent supply of resistors, caps and pots. Can acquire LEDs, op amps, transistors, etc as necessary. I taught HS physics a long time ago, so I know the challenges of doing a lab in 50 minutes. But I’m open to advice. I’d also love project suggestions for me to give to the class. What type of circuits are cheap (<$25?!?) and easy to build, yet still cool?
Thanks!
I recommend you see if you can get a copy of this book for every student- It will help them tremendously:

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

As for what kind of circuit- I would pick something, or several somethings that show them how to achieve something in the real world- not just theoretical. For example- Something that can sense when water is pooling on the floor (simple closed circuit, with an alarm), or something. I recognize that may be too simple- but if they can see how it can be applied to something real in their world, it has a much better chance of being exciting, of value and interest.

Like solar things- Maybe a solar powered cellular charger- can be used for cellphone. Easy to make and demonstrate with very few parts, but has a real-world application and keeps in the 5V world. Can power their arduino, etc.

Hope that helps

#### dl324

Joined Mar 30, 2015
15,510
if you just screenshot the Eagle schematic it has all those +s everywhere, grab points for each component. So I export the image(gets rid of +s), and I prefer it in color although there is a B/W option.
If you print to PDF, the origins of things aren't printed.
I’m not sure why color would be bad? It distinguishes between different type of components.
Why do you need components to be color coded? Wires and buses in Eagle are different colors, but I print everything in B&W and never have a problem telling one from the other.