BlinkyBadge

In the summer of 2019, I got a request from one of my colleagues to enable STEM learning for girl students. Most girl students were disinterested in Arduino or programming, so we had to create something which would get them interested in these topics.

We decided to not jump directly to Arduino, but take a simple step of learning how to connect components on a breadboard, how to read a circuit, what each components does, etc.

With that goal in mind, we decided that blinky lights in a certain pattern would be a good first project.

We chanced upon a youtube video which showed exactly this. Here is the video.

Supplies

BC547 Small signal Transistor x6

47uF Capacitor x6

10kohm resistor x6

330 ohm Resistor x6

5mm LED x6

9v Battery

Step 1: Testing and Verification

The creator of the video is using what is known as a ring oscillator to feed input from one stage of a circuit to another. When the last stage is reached, it feeds it back to the first one, thereby making a ring. It uses readily available components and can be made on a breadboard easily.

Step 2: Testing on Breadboard

Before I jumped to making a PCB, I did some tests on a breadboard to understand how the circuit works and what are its connections.

Step 3: Figuring Out How to Power It

In the original idea, the power is coming from a 9V battery, which is not the right kind or a wearable locket. We did a test with a CR2032 coin cell and it worked very well.

With all parts checked and confirmed, it was time to make a schematic and a PCB.

Step 4: Making a Schematic

I used EasyEDA (www.easyeda.com) for my schematic and PCB design. There is nothing to install, all libraries are online, and the autorouter is pretty solid for simple designs.

I first translated the whole circuit to schematic, made connections on the software, and then looked for the right kind of switch and battery socket. I found both of these on Easy EDA.

One of my requirements was to have the battery socket polarized. Even if the child wished to put the battery in reverse, they could, but the circuit would not be powered. To make the badge almost the size of the cr2032 battery, I figured that it was not possible to do with through hole components. I used a mix of 0603 and 0805 packages for resistors and LED's, the capacitors were also 0805 package. These can be easily soldered by hand and a fine soldering tip.

Once you create a schematic, it is worthwhile to check connections and review multiple times.

Step 5: Designing the PCB

This is the challenging part.

Designing a PCB requires you to be creative as well as be practical in how you have to lay out parts. The creativity is needed to make the PCB look appealing to students, and the practical nature is required so that you can safely and surely solder parts. You also have to keep in mind how will the user use the pcb.

With all that in mind, I exported the schematic design to PCB using Easy EDA.

Normally, Easy EDA will give you a square PCB outline, along with all parts bunched together.

Because there is no easy way to make a circular outline of the PCB, i used my favorite vector graphics tool called Inkscape.

Inkscape allowed me to make a outline in the shape that I wanted, and I can import the outline as a dxf into EasyEDA.

Once my outline was nailed down, Easy EDA allows you to arrange the parts in a circular manner using the Arrange Option. You can specify the radius for the arrangement and Easy EDA will put the parts around a circle.

Step 6: Routing

Once you have put the parts in their positions, it is time to route. Routing is the process of converting the connections in the schematic to tracks on the PCB. Sophisticated algorithms will take the connections and make the routing patterns using design and manufacturing rules.

The traces are placed on both side of the PCB ( Top and Bottom) and are connected with holes called Vias.

Once routing is complete, it is time to do a Manufacturing check and send the board designs ( called gerbers) for manufacturing.

Step 7: Send Gerbers for Manufacturing to JLCPCB

Easy EDA has integration with JLCPCB, which is manufacturing facility based out of Shenzen, China.

You essentially export your design, and it pops the above screen. You click on Order at JLCPCB, and it will take you to the JLCPCB ordering page.

You can learn about the ordering process in the video.

Based on your quantity of PCB and delivery address and shipping method, it takes somewhere between 3-10 days for the PCB's to arrive. I received mine in 6 days.

Step 8: PCB's Arrived

My PCB's arrived in a vacuum sealed bag and nice packaging.

The vacuum sealed bag prevents any kind of tarnishing of the tracks and pads on the PCB, so you should only remove it when you are ready.

PCB quality was very good and I was very happy with the outcome.

Step 9: Soldering and Results

I quickly sat down to solder these by hand to test. I used a Micro Soldering iron to solder all the parts. My first soldering exercise was shabby, but it works.

I also found a beaded chain with a ring to put it around the hole in the pendant.

I did some tests and added different colored LED for a Christmas'sy feeling with red and green.

Step 10: Making Your Own PCB

Now that you have a fair idea of the process, why dont you jump in and make your own project. Start with something small, and then grow from there.

Ask me questions in the comments, I will be happy to answer them.

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