Cardboard Knife Switch

For many electronics enthusiasts there is a special place in their heart for knife switches. At least that’s the case for educators I’ve worked with the past decade or so. My guess is it has to do with the simplicity of the knife switch in explaining how a circuit works. Is the circuit opened or is it closed? A knife switch provides a visual demonstration of this like few other switches do nowadays.

Knife switches are not used for most modern day circuits as they have been replaced by switches that are safer at high voltages, but since we work with low voltage circuits in educational settings this DIY Cardboard Knife Switch is perfect.

I’ve talked to a few educators and heard complaints about how expensive the old style knife switches are. (You can buy new “cheap” plastic versions for about $2 per switch, but the ceramic ones are often $10 or more.) I thought I’d lower the curve by creating a cheap DIY version that can be made with Maker Tape.

There’s a template that can be used to make one from cardboard or other material that’s got some rigidity and thickness to it. Cardboard is great, foamcore could work, cereal boxes are too thin. The template expects some cardboard and a way to cut it, which could be an X-ACTO knife, some scissors, a razor blade, or even a laser cutter.

Once you have your four pieces you attach some conductive Maker Tape, poke some holes for the brass fasteners to go through, and you’re nearly done!

Assemble the four pieces using the brass fasteners to hold them together and to act as a pivot point for the lever and you’ve got a knife switch. It may help to pinch the top of the two outside pieces a bit narrower so the knife is guided into place a bit better. (You’ll see this tip and more in the PDF guide.)

Besides the Brown Dog Gadgets Project Database, you can also find this project on Instructables.


Seeeduino Nano

The folks over at Seeed Studio sent me a Seeeduino Nano to check out. I’ve used a lot of Arduino boards over the years, including plenty of cheap Arduino Nano clones. Most of the clones have worked fine but every now and then I’ve seen a bad one come through. The Seeeduino Nano is a nice quality board with a little extra to make it useful for beginners or people more interested in making things quickly/easily than they are soldering wires.

One interesting thing about the Seeeduino Nano is that it used USB-C to connect to your computer. While most of the Arduino UNO boards I’ve used still use USB type B, and lots of other boards use Mini-USB or Micro-USB, the Seeeduino required a USB-C cable. Luckily, I had one on hand. If you don’t already have a USB-C cable, you’ll need one for the Seeeduino Nano.

My favorite part about the packaging of the Seeeduino Nano is the warning on the back that says “Best to keep away from fire”, mainly because I’ve worked on multiple Arduino projects that specifically involved fire… But I digress… for most people keeping away from fire is probably a good idea.

Here’s the top view of the Seeeduino Nano next to a ELEGOO Nano board. You can see the difference in the USB connector and a few other features. One difference with the ELEGOO boards is that they come with the header pins included but not soldered in place. (Here I’ve soldered them to the board.) There are times when you don’t want header pins solder into place. My guess is that for the target market of the Seeeduino Nano, the pins already installed makes sense.

Another thing about the ELEGOO boards is that I can’t easily find them listed on the web site. Here’s a post about them, but in the past if I’ve purchased them I’ve found them on Amazon for a price close to the Seeeduino Nano, though I’ve only seen them as a 3-pack.

(Note in the photo above the boards are the same dimensions, the Seeeduino is just on an angle due to the extra connectors on the top.)

Since I had a project already done with a Nano in place (via my Anrduino Nano Breakout Board) I just swapped in the Seeeduino Nano, uploaded the code, and it worked great.

Where the Seeeduino Nano really shines is the capabilities it has with the Grove system from Seeed Studios. If you don’t want to solder, and also don’t want to stick a lot of wires and components into breadboards, the Grove system might be what you are looking for. Again, I see this is a match for those who are more interested in the code than the wiring of electronics, or for workshops where soldering might be a concern (with kids or those not able to solder for other reasons).

In the photo above you’ll see the Seeeduino Nano along with the Grove Shield, a Temperature & Humidity Sensor, and a connector wire.

It’s also worth noting that the Seeeduino hardware and Grove system are open source, and others have embraced Grove. Adafruit has a Grove Shield for Particle Mesh and Feather Boards.

Above you’ll see the Seeeduino Nano plugged into the Grove Shield which has a Temperature & Humidity Sensor sensor attached. This takes seconds to connect versus soldering things or plugging things into a breadboard. When I taught basic Arduino classes I always told students to unplug their Arduino when they wired up the breadboard, and then to double-check the wiring for errors before plugging in the board again. The Grove plug-in system eliminates much of that guesswork. You can’t really plug things in backwards.

Here’s the Temperature & Humidity Sensor. I’ve worked with logging temperature and humidity before, so I’m not really new to this. The new part is the simplicity of just plugging things in.

I grabbed the example code Seeed Studio provided and had a few issues. Nothing I couldn’t fix, and I did open an issue about it. In the end I grabbed Adafruit’s library for the DHT Sensor as well as the Adafruit Sensor library (which is required by the DHT library) and got things up and running. If you’re not interested in downloading zip files from Github you can also install these libraries right from the Arduino IDE.

Overall the Seeeduino Nano is a good quality Arduino board, and the Grove system makes it very easy to get up and running. In this specific test I did run into some trouble with their example code, but in most cases those issues are solvable, and there’s probably an alternative example or library out there that will do what you want or need.

Finally, here’s a short video of the game scoring system I mentioned above. The Seeeduino Nano is taking input from a number of pins (that will eventually be triggered by switches or buttons) to keep score, where each pin is a different point value, and then using the piezo speaker to play a sound for each point value as well as displaying the points on a small LED display.


Rapid On/Off Time (Almost)


I should have known this project was doomed from the start. When I laser cut a piece of paper to test the fit of the components, I somehow managed to flip around the holes for the LED displays, so I ended up building it flipped from what I designed. If that was the only issue, things might have been okay…


Hey, things fit! This was all good (though as mentioned, flipped) and as a front panel it looks fine. Let’s move on to the back of things…


Still good! A few laser cut spacers to get the LED panels flush. The rotary encoders and the outlet are all good. Of course we still need to add wires to get it all connected.


Wires in place. Not bad. I added an Arduino Nano with one of my breakout boards and screw terminals, and there’s a relay module to be controlled by the Arduino. All good.

The idea was that the first encoder would control how many seconds/minutes the outlet was on and receiving power, while the second encoder would control how long the outlet was off or not receiving power. This would allow me to control a 120 VAC device turning it on and off for set amounts of time. (I know, I probably could have used a timer relay, but I wanted to build something.)

Somehow, I never quite got the code to work. Maybe there were some weird issues with the encoder library, or using two encoders, along with the LED panels, I don’t know… but I tried for a few hours to get it to do what I wanted, and it never did. Typically with code issues I bang at it until it works, but for this I just sort of gave up.

In the end it didn’t matter much because I ended up using a variac to lower the voltage instead of togging the full 120 VAC on and off. I also ended up stealing the LED panels and the Nano for another project that had to be done in a hurry. I’ve still got the other parts in place, so who knows? Maybe I’ll return to it in the future…


My First Noisemaker

Noisemaker from the 1980s4938

I came across a treasure in one of the (many) boxes of “old things” in the basement. What you see is a Radio Shack project box with a speaker and a switch on it. Yeah, it’s a noisemaker, and I built it in the mid-1980s.

Fun fact, I used to do electronics in high school, and while I’m not sure this was a project we did in class, I’m guessing I may have built it around the time I was in school. It was probably around 1985 or so, if I had to guess. (I think I took two years of electronics classes.)

Noisemaker from the 1980s4939

The speaker has a “grill” that appears to be made from a metal screen, maybe from an old scrap window screen? I do know it would have been built with whatever stuff was around the house. I think I used Elmer’s glue to attach the screen to the speaker. It seems to have held up! The lettering for the “ON” label was most likely done using Liquid Paper and there’s a bit of clear Scotch Tape covering it as a protective layer. This also held up well!

Noisemaker from the 1980s4940

There’s a hole in the case. I’m not sure why. If I had to guess, I probably burned it with my soldering iron. I should say “Solder Gun” because at home we had one of these, and I don’t know if it belonged to my dad and I used it, or he bought it for me, but I do remember it wasn’t easy to solder with. At the time I didn’t realize this wasn’t the preferred tool for delicate electronics work…

Noisemaker from the 1980s4942

It looks like the soldering joints on the speaker held up fine… not so much for the masking tape, which dried up and lost its “stick”. I guess I just taped the speaker down, and used the tape as an insulator for the speaker contacts. (I did not know about hot glue yet.)

Noisemaker from the 1980s4945

Let’s pop this sucker open! Solid core wire and a 9 volt battery connector are visible. There’s also a piece of paper that I assumed was to insulate the metal battery housing from the electronics. And then…

Noisemaker from the 1980s4946

I took out the piece of paper and… oh my gawd, I actually documented this thing. There’s a circuit diagram and a Bill of Materials! This explains so much about my life, and honestly, I’m sort of proud of teenage me. Good Job, Petey!

And no, it’s not a proper schematic, but it’s approximately how I document most of my work/projects nowadays, using circuit diagrams, like you might create with Fritzing.

Noisemaker from the 1980s4947

Finally! We’ve got a perf board inside with a few components soldered onto it, and and rudimentary strain relief by running the wires through the mounting holes of the perf board. Well done, Petey!

Noisemaker from the 1980s4949

Let’s flip it over and… oh my gawd, the soldering! Sheesh! Now I am embarrassed! But this does lead me to believe I did this project at home, since that’s where I was using a giant soldering gun and giant solder not quite suitable for delicate electronics. Oh well, at least my soldering skills have improved since the mid-1980s!

Oh, in case you’re wondering how it works, look at the diagram for a clue. You touched the metal bolt sticking through the enclosure and the top metal piece of the enclosure, and you completed the circuit, and could get weird tones based on how much you touched and how hard you pressed. I was really hoping to include a video but sadly, it did not work after 30 years of sitting in a box. Drat!

(And yes, I’m really tempted to build a new version of this to see what it sounds like!)


PCBWay Prototyping Service


The crew at PCBWay got in touch with me to see if I’d like to try out their service. I’ve used other PCB manufacturers in the past, so I figured I’d give PCBWay a try to see how they worked. The ordering process was not the smoothest, but the boards turned out well, were very affordable, and they got to me pretty quickly.


I designed this PCB years ago and I’ve used them a lot in my noisemakers and while I might modify them in the future, they are still pretty useful, so I figured I’d make more.


I had my Gerber files ZIP’d up and ready for upload, so I started the process with PCBWay, which I assumed would be similar to other PCB manufacturers I’ve used. Yup, pretty close. Note that for color you can choose green, red, yellow, blue, white, black, or “none” at the same cost, but choosing purple, matte green or matte black cost bit more. (Not quite double, but more than just a few bucks.) I’m not sure what “none” looks like, but I am curious.


So I added the boards to my cart, and I first noticed that I could not change the quantity. This was a little annoying, as I wanted to try different quantities to see how it affected the price. You can do that, but only at the first step in the process, at the “Online Quote” step, not once it’s in your cart, so make sure you know how many you want before your add them to your cart!

When I went to checkout I then found out I could not check out. Right, seems my boards were “Subject to audit.” Yes, they had to be approved by someone (a human I guess) before I could order them, which seemed weird. (Notice the yellow highlighting I added to the cart image above.)


Now, this is partially my fault, as I didn’t see this the first time I uploaded files. There is a little bit of text on the upload form that shows it could take “10min to 1 hours” for approval. I’m not sure exactly how long it took, as I did this late one night and didn’t get an email about approval until the next day. This was the most annoying part of the ordering process. When I want to order something I don’t want to have to wait hours, or even one hour between putting it in my cart and being able to order it. Perhaps they could make it so that you can place your order, and then if not approved for some reason (?) they could refund the order. Or who knows, maybe this whole “approval” thing is due to some new tariff laws. I have no idea.


Like I said, pricing is good. I got 75 boards for $32. That’s about 43 cents per PCB. These are tiny boards though, so obviously the price per board goes up when you get larger boards. With approval completed (by some human, I guess) I was able to move on to shipping options.


I went with shipping via DHL, which came in at $21, so the order total for 75 boards ended up being $53, making each board cost approximately 71 cents. (Obviously ordering more would probably bring that price down, but I really doubt I need more than 75 of these right now.)

I uploaded the PCB files on July 21st, and they were approved and ordered by July 22nd. Manufacturing was completed by July 25th and they were then shipped via DHL July 27th and I got them by July 30th. That’s about an 8 day turnaround for these printed circuit boards. (With some weekend days in there.) Not bad! For US shipping DHL is probably the best option for getting them fast. There were two cheap shipping options, one being an ePacket (which seems to be how I get most of my eBay electronics delivered) which was $8 but had a 10 to 15 day delivery time frame. There was also “China Post” option which was $7 but showed 25 to 40 days for delivery. Wow. So the ePacket is not too bad if you do not need your boards in a hurry.


The boards from PCBWay look good and got to me fast. They were also very affordable. Overall it was a good experience except for the issue of having to wait until files were approved before ordering and not being able to change quantities once the item is in your cart.