This is the fifth part of the meta-tutorial, where I talk about designing a cheap plant watering sensor. If you did not already read the first, second, third and fourth part, please do it now. These parts contain a lot information which lead to this point of the tutorial.
The fourth part ended with step 20, where I did usability tests and stability tests using the preliminary firmware. This article will focus on designing the final board for the project.
Step 21: Design the Final Board
Designing a good board is like one of these puzzles with quadratic tiles, where you try to lay down a 3✕3 set where all edges match. Often a small change result in many follow up changes, so you have to rip-up a lot of routes and design them in a new way.
My goals for the board were:
Everything, except the two LEDs, should go to the top side of the board.
Reduce the amount of vias to the absolute minimum.
Create a ground pour, especially around the oscillator part, to reduce noise.
Move the button as far as possible from the oscillator to minimise the influence if the user presses the button.
Make it as small as possible.
I worked with small iterations, checking the design after each iteration and checked the design against my goals. To keep track of the changes, I versioned each larger iteration. This way I could go back at a later stage for comparison or if a change did not turn out well.
I worked with Autodesk Eagle to create the board. This tool is in the current state far from perfect, but it is cheap and has all required features for the task. For me personally, these are the features I need to design a board:
Smart routing editor which is linked to the schema.
Quick and easy way to create vias and see the required connections.
Good library support for symbols and packages.
Design rule checks.
Quick board preview to check label placement and design.
I just finished part 2 of the project description for the Outmoded Sequencer. In this second part I describe the steps from the prototype to the final device. I copied the preface from the page after this link .
Building the Outmoded Sequencer was a really interesting project where I learned a lot. It was the first project with a custom designed PCB. Usually I just solder everything onto stripe boards, because I only produce one single device. The complexity of this device with the matrix forced me to design a proper PCB, soldering everything on a stripe board is feasible but requires more space and a different approach for the matrix.
Not everything turned out as well as expected. First there was the idea with the matrix using steel balls as switches: Even with the magnets generating a certain force to the pads, the steel balls do not connect as reliable as I would like they do. As you can see in the demonstration video, it is still possible to have a lot of fun playing with the sequencer – however better connections would make the experience even better.
Should you build your work Outmoded Sequencer? Yes, absolutely! But you should definitely use a different approach for the matrix. Best first only experiment with the matrix part until you have a working solution there before you add the other parts around.
Should you use the provided PCBs? No, better design your own board especially implement the matrix in a different way.
Should you use the circuit design as provided? Yes, definitely! The design is, in my opinion, a very good start and should give you a reliable and working device with minimal effort. Keep in mind: This is a minimal design and there and many ways how to improve certain aspects of the circuit. So feel free to address the problems if you have components left, to spend on this project.
Hurray! I just finished the final Outmoded Sequencer device. The tuning of all frequencies was way faster than I expected, because I used a new method. Have a look at the following photo gallery before I tell you some details.
You can see the device is build like a control desk, with the PCB a little bit at an angle. The left knob on the top controls the speed of the sequencer and the right one the volume.
A did a few tests already and the idea with the steel balls is working, but not great – just ok. So sometimes they do not connect and you have to move them a little bit until they make contact again. Most of the positions are working always without problems.
It is a great fun to play with the device, changing the pattern while the melody is playing. Now everything is finished, I also can move two steel balls at a time which can create interesting variations.
Next I will do a detailed video, where I demonstrate the final Outmoded Sequencer. It should give you a better impression of the device in action. I will also setup a complete filter chain, so you can experience how easy you can use the sound of the sequencer as input to do various interesting effects.
I will also add the second part of the project page, where I explain some of the details about the magnet matrix and how the whole thing is built.
There are seven absolutely perfect PCBs left, so I think about to give them away if someone is interested into building the project. But be aware, this is no kit, just the plain PCB. You also have to use the exact same components as I did – or at least ones which perfectly fit into the holes. All components should be available to buy at various stores, and I will provide the exact part numbers.
Here a short update on the progress with the final Outmoded Sequencer project. I did the whole assembly of the final PCB and connected everything. You can see part of the soldering process in the following video:
I accidentally cut a route on the bottom of the PCB, so I had to fix this with a short wire. It is not visible on the final device. The magnet matrix mentioned in a previous post is already securely fastened to the bottom and holds the steel balls in place.
There are only the final adjustments of the frequencies left to do. I have to tune each tone and add the last four missing resistors.
The final black and gold PCBs for the Outmoded Sequencer arrived. They really look great with a nice contrast between the solder mask and the silk. The surface is somehow glossy and the routes are barely visible under the black solder mask. Now I really hope I will not find any further problems with this PCB.
This nice PCBs were produced by PCBWay. As you can see, the quality of the PCB is very good. They produced it in three working days and it was shipped in three days via DHL.
The final version is 8mm wider and 10mm higher than the prototype PCB. You can also see how I rearranged the components to move the matrix more to the center.
A very interesting fact is, that I could simplify the routing, because I mounted the resistors and diodes back in the normal horizontal way. This created space under the components which I could use for the routes. Here the routing of the final board: