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• Fetch V2 - Massive Hardware Upgrade

  Applied Procrastination • 08/24/2021 at 17:12 • 0 comments

  We've upgraded the Fetch hardware drastically! We are super excited to finally share what has been going on behind the scenes on this project since before COVID hit and slowed down our progress. First, have a look at our latest project update video, and then dive into the technical details below.

  Project Update Video

  Technical details

  Why redesign?

  When developing the first version of Fetch we quickly encountered a few problems that could only be solved with a complete PCB redesign. We had made the electronics too generic, and hadn't considered actual integration too thoroughly. So, when we actually attempted to attach wires to it for the first time, we soon realized that the wires weren't long enough to reach where we wanted them. Additionally, since we weren't quite sure how we wanted the software architecture to be, we implemented a lot of features that were more in the "nice to have" category than in the "need to have" category, resulting in an overall bulky design. 

  Apart from a poor form factor, we also soon discovered that we needed to be able to control the magnetic field strength of each individual electromagnet. The reason that this is necessary is because gravity will pull the ferrofluid down towards the bottom magnet if several pixels are ignited in the same column. The simplest way to control the magnetic field, without having to deal with any additional complex adjustable current circuitry, is by pulse-width modulating (PWM) the supply current that is fed to the electromagnets. We didn't really have a good way to do this though, as the PCBs were based on shift registers that parallelized a stream of serial data in order to open or close gates in ULN2004 Darlington transistor arrays. This means that, if we wanted to implement PWM, we had to do it in software, and the software would be highly resource consuming given that there is a lot of serial data to shift out in order to even get close to a decent PWM frequency. 

  Design requirements

  So when redesigning the board we had much stricter design requirements, both in terms of form factor, and in terms of necessary features. 

  • We wanted one single board controlling each row of electromagnets to simplify the code (and we conveniently had the same number of outputs on our PSU as rows in our electromagnet matrix, which steered us towards one board per row rather than one board per column). 
  • We wanted the board to have a thin and wide form factor so it would fit behind the electromagnet matrix and all the wires would reach their dedicated connector.
  • We wanted to use an IC that could handle PWM for us, preferably through an actual serial protocol rather than just bit shifting.
  • We needed to keep the things that worked well in our previous design (such as an alternating pattern of electromagnet polarities designed into the boards rather than having to manage electromagnets with different polarities decided by their connector orientation). 

  The trick

  Three of the mentioned requirements were easy to implement, but finding a PWM capable IC that could provide enough current for our needs proved more difficult. After pondering a while we realized that there are a ton of PWM capable ICs in the LED driver segment. 

  Maybe we could just use an LED driver to power our magnets? The problem with that idea turns out to be the maximum current rating. LED drivers are typically not rated to sink more current than what is necessary to turn on an LED or two. While a normal LED can consume a fair bit of current (typically up to ~20mA), it's generally not even close to the consumption of an electromagnet (~200mA). 

  Ok, so maybe we could combine an LED driver with a transistor array in a similar fashion to how we combined shift registers and transistor arrays before?...

  Read more »

• Real Time Clock Module

  Applied Procrastination • 12/19/2019 at 19:53 • 1 comment

  We've added a small perf-board that breaks out I2C-SDA0 (PIN 18), I2C-SCL0 (PIN 19) and 3.3V (which we for some reason hadn't already expanded). The perf-board also hosts an Adafruit DS3231 Real Time Clock (RTC) Module, which means that we now, after some minor code-adjustments, have a "clock mode" for our display.

  When operating in "clock mode", the display will show the time with one minute resolution. Every time a minute has passed, the display will load a new animation from the SD-card and display it. We change modes with a 4-way switch that is yet to be documented (our guess is that the current code might not be self-documenting 😅) . 

  We'll publish some logs documenting the switch and some buttons we've added, for easier operation, at a later time.

• Fetch is DONE!

  Applied Procrastination • 11/29/2019 at 14:28 • 0 comments

  Oh, wow. It took us two years from start to finish, but the display is actually done. 
  

  We've compiled a series of sweet sweet animations and spent a long time perfecting this video. We hope you enjoy it:

  
  Since last time we've hidden the cable chaos. For the initial version of "Fetch" we wanted to use laser cut plywood as a chassis, because it's a very replicable and simple solution. We will look into a making a neater metal finish in the next version, which will be considerably sleeker, for an even cleaner look.

  For our own convenience, we also added a few buttons and switches that makes it simpler to show a variety of animations when displaying the project at maker festivals.
  

  We make the animations in Aseprite, a powerful and free* pixel art editor, and parse them into a format we've found easy to read on the Teensy 3.6 that's at the heart of the platform.

  (*As long as you can compile the source code yourself. )

  ---

  Future projects

  While Fetch is now complete, we are not done working with ferrofluid, or electronics for that matter. We are currently researching ways of making a "flat screen" version, and even much smaller ferrofluid displays that are cheaper to replicate. We are also working on implementing more software features, like videogames, in the version we've already made. This paragraph marks the end of the project, but not the end of our ferrofluid display endeavours. Stay tuned!

• Code Optimization

  Applied Procrastination • 09/11/2019 at 19:15 • 0 comments

  As we have already revealed here on Hackaday.io, we recently upgraded our system with a Teensy 3.6 (from an Arduino Mega). We also did various changes to our code in order to make it run faster, so that we could implement PWM in software and have it perform reliably. We've already shared most of the improvements we've done, but now we've also compiled a video showing how it looks in practice:

• Electronics Assembly and Full Integration Test

  Applied Procrastination • 08/10/2019 at 12:24 • 0 comments

  Although the project is new here on Hackaday.io, it has already been going on for a while. We have several build episodes on YouTube, but in our most recent video we integrate the full system and test it after first having assembled and tested the electronics. 
  
  Everything is open source, and the files can be found below. However, we do not recommend anyone to attempt to rebuild the project in its current state. The electronics especially require a big revision (version 2 will be started later this fall).
  
  Schematics:
  https://cdn.hackaday.io/files/1670567147323904/Applied-Procrastination-Fetch-Driver-Circuit-v1r2.sch
  PCB Layout:
  https://cdn.hackaday.io/files/1670567147323904/Applied-Procrastination-Fetch-Driver-Circuit-v1r2.brd
  
  (work in progress) Firmware can be found on: 
  https://github.com/SimenZhor/FerroFetchFirmware

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