After building the prototype of the Outmoded Sequencer I started working on the final device. This second part describes all steps and details of the final device.
Table of Contents
- Designing the PCB
- Building the Magnet Matrix
- Preparing the PCB
- Soldering the Components to the Board
- Building the Case
- The Finished Device
- Tuning the Notes
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.
Designing the PCB
The first step was to build the final PCB. Here I learned a few things from the prototype:
- Vertical mounted resistors save space, but there is less space left under the resistor for routes. Interestingly this leads to longer routes and more vias. So I went back to regular mounted resistors.
- I increased the size of the PCB a bit to make room around the matrix, which is needed to be able to pick up the steel balls.
- Moving the red LEDs to the left side not only looks better, it also simplifies the routing. It also moves the matrix more into the center of the PCB.
- I also moved the chips as close as possible to the locations where they are used.
- The bottom mounted potentiometers were a bad idea. I just added pads to connect them. This also simplified the routing, because I could move the pads closer to the sections where they are used.
- I added A on/off switch that was missing.
- To connect the sequencer to an audio interface, I added a line out jack which automatically switches between the built-in speaker and the output.
Here a comparison between the prototype and the final PCB:
Building the Magnet Matrix
Next I build a matrix with magnets to hold the small steel balls into place. This matrix of 8×8 neodym magnets exactly matches the pads of the board. It is later mounted below the PCB, so there will be one magnet for each pad on top.
I am using these small, but very powerful neodym magnets. They have a diameter of 4 mm and a length of 5 mm. You can get this magnets, and many other shaped magnets, from Supermagnete, they deliver the magnets to almost all European countries.
I start with a piece of plywood. Using the holes in the PCB as a template I make marks into the plywood using a stitching awl. Next I drill 64 holes with a diameter of 4 mm into the plywood.
To fasten the magnets I glued a thin paper on one side of the plywood and put a small amount of glue into each hole from the other side. Then I place one magnet in each hole and make sure they stay in place.
This is very difficult, because this magnets are really strong and you have to keep them from leaving their holes and stick together. If the holes are precisely made, the magnets can not move easily which prevents them from popping out of the holes.
Next I add a thick layer of black acrylic paint to the wood and magnets from the other side. Dry acrylic paint gets very tough and will stop the magnets from moving around or even pop out of the holes.
The paint and glue has to dry for 24 hours, then I cut the plywood to the final size. I use an utility knife to do this.
Now I add another layer of black acrylic paint to the whole block. I also paint the other side of the magnet matrix which will be visible through the holes of the PCB. This has to dry for another 24 hours.
Preparing the PCB
In the PCB are just 64 small holes as lead for the real holes of the matrix. I use a small 4mm drill to create the grooves for the steel balls in the matrix.
Soldering the Components to the Board
Next I solder all components to the board, starting with the smallest ones. See the following video for the soldering process:
After soldering the components to the board glue the magnet matrix to the bottom of the board. Aligning the magnets with the pads is essential in this process. For this reason I marked the center of the four corner magnets, this marks were visible through the holes from the top side and allowed a precise alignment.
Building the Case
First I cut the base plate to the right size. Here I used the exact size of the PCB and added some room for the control plate on the top. I used the dimensions 137mm × 123mm for the base plate.
Next I cut the control plate with the dimension 137mm × 50mm and used the PCB and top plate to drill 3mm holes for the M2.5 screws and spacer. I also added the holes for the speaker and the two potentiometers. Afterwards I spray painted the two plates and let them dry for 24h.
The assembly for the control plate is quite simple. Fastened the two potentiometers in the plate, cut the axis to the right lengths and added the knob. I also glued the speaker at the right place. Later I soldered wires to all parts, ready for assembly.
I added the battery holder on the base plate by simply drill very small holes at the right locations through the plate and glue them to the base. Then I soldered wires to the connectors at the bottom side and used two additional holes to get the power wires back up to the PCB.
In a last step I combined everything and soldered the wires from the battery, potentiometer and speaker to the PCB.
The Finished Device
Everything in place it looks nice and I like the different colours with the contrast to the black board and plywood.
Tuning the Notes
To tune the individual notes I connected the device to an audio interface. Using this input I used audio analysis to determine the precise frequency of the signal. Tuning the tones this way was simple and fast.
The following video is showing a small performance using the Outmoded Sequencer. I deliberately kept the audio simple without fancy filters to give you a good impression of the actual sound. At the end I add some simple effects to show you the potential of the sound if processed with any audio software.
- The schema for Eagle 7.7
- The board for Eagle 7.7
- The Gerber files for the final PCB
- The final schema for the project as PDF
I hope you enjoyed this project description and I could you inspire to build something similar. If there is anything missing on this page, please leave a comment.