Raspberry Pi is a powerful but small Linux based computer board that gained its popularity in the hobby world. It has everything you need to build a computer except display. Since there are no DSI based display modules available, people try to solve this problem in several ways. They use HDMI based displays, composite video, serial monitors. Probably most of small projects rely on GPIO where they plug in their custom boards with various types of LCDs. This seems to be OK, but running such displays usually require additional driver/software to run and it occupies I/O pins, that can be used for other purposes. While we are waiting for official Raspberry Pi DSI display we have to deal with those workarounds.
The choice is really big. You can find may types and sizes of displays driven through GPIO. Percheron Electronics Ltd are running kickstarter campaign where they offer to give a shot with their offered e-ink display solution. It comes on a module board that plugs in to Pi’s GPIO. Display resolution is 264×176. The main advantage of using such display that it practically requires no power supply when displaying statical information. It only draws a bit when changing its contents. Display module comes with RTC clock built in which can be used by Raspberry Pi to track time precisely or work as a clock for display itself. E-INK display is great choice if you plan on building battery powered project where you need to represent information as text or graph. They are not meant for high FPS, but for text information like clock, weather, social feeds or basic B/W graphics it is great.
The easiest way it to use smart phone with GPS locator. When you park, simply record your location and when you need to find it use navigator which guides you to its place. If you don’t have such phone and want to build one, follow msuzuki777 instructable where he builds car tracker.
Device is pretty simple when building using modules. So here he uses Ublox NEO-6M GPS module, LSM303DLHC magnetometer, custom Arduino, Nokia 5110 LCD and Lithium battery. This locator simply remembers coordinates where your car is parked. When you need to find simply turn on and you will see how far you car is and what direction you need to go thanks to magnetic sensor based compass. You can find more uses of this devise. For instance when hiking – you can remember start location and let it guide you home when done.
Common hobby BLDC motors are meant to run on relatively high speeds. Take any plane, quadcopter or boat – low speeds aren’t required here. For high speed rotations BLDC drivers rely on back-EMF (or Hall-sensor) to sense rotation speed. Berryjam decided to see how slow he can run those motors with Arduino and triple half bridge chip – L6234.
Since standard speed controllers use square wave signals to drive the coils that aren’t noticeable in high speeds (maybe too noisy), in slow speed rotations steps become choppy. So here he used sine wave shaped current modulated by Arduino PWM. There are two options – using sine wave PWM or Space-Vector-PWM (SVPWM) – they both work well. Tests show that with standard BLDC motor he was able to get 2160 steps per revolution, or 0.16 degree precision which can be made even higher. It is hard to tell from video, but it seems that BLDC motor doesn’t seem to be good choice for stepping applications, since it is not designed to step and hold. Maybe it would find its place where very slow and accurate driving is required.