2019 year [Simen] with [Amud]Two students from the University of Oslo set out to design a unique open source display. The result is Fetch, a display that uses electromagnets to suspend ferrofluid over 252 “pixels” on the screen. Due to the impact of COVID, after some delays, They recently announced the displayed version 2.0 on their project page.
Although the two managed to overcome the mechanical challenges associated with the use of ferrofluid fairly easily, they were quickly hindered by electronic devices. The use of liquid-containing electromagnets presents a unique challenge. The magnet cannot be turned off, even for one millisecond, otherwise the “pixels” will fall to the bottom of the screen. This immediately precludes any type of multiplexing, meaning that everything must be driven in parallel. As if this is not difficult enough to solve, the effect of multiple electromagnets being activated next to each other will change the way the ferrofluid flows. This means that the strength of each electromagnet must be adjusted according to what is currently displayed, not just being turned on or off.
All of this, plus other overhead, such as generating pulse width modulation for the input, is too much for a single microcontroller. Therefore, the couple set out to design a better version of the electronic product to ease a lot of hard work. At the same time, they decided to make some mechanical optimizations; they redesigned longer and thinner circuit boards so that they could be cleanly installed behind the row of electromagnets they controlled.
The new board uses PCA9685 IC, which can control up to 16 channels of 12-bit PWM through i2C, which is very suitable for the size of the display. Since the IC cannot provide enough current to drive the electromagnets, it is paired with the ULN2803 Darlington transistor array, which can provide up to 500mA for each electromagnet.
Have prototypes on hand (and some messy wires), [Simen] with [Amud] Let the new driver board work beautifully, displaying text in a fascinating way that is unmatched by ordinary monitors. Watch the video after the break to demonstrate the operation of the new controllers and get an in-depth understanding of their development process.
Want to know more? Check out our previous article about Fetch! Or, if you are looking for another cool way to use ferrofluid, how about making it dance in custom speakers!
[Main image animation is slowed by a factor of 3]