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Which MCU?


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Hi all,

I've been lucky enough to have a bit of time to start playing around with my electronics gear. I would like to make my own tilt/pan head tracker and later on work towards autonomous flight.

Currently I have an EasyPIC4 development board which will allow me to play with any PIC up to the 18F range. I've had it for years and have had an active interest in PIC's but very little time to get hands-on. So far I've experimented with decoding a servo signal from a R/C receiver (nav lights project) and taking readings from a two-axis accelerometer then outputting them on an LCD display. I'm now attempting to cleanly drive 1 - 2 servos; something which sounds a lot easier than it actually is!

After browsing various forums and looking at the kits on offer from SparkFun, I wonder whether a PIC is the correct tool for a UAV type project. I have noticed that quite a few projects are using the Phillips LPC2148 ARM7 chip. From browsing the examples it looks like driving servos etc is much easier with this chip using the built in PWM functions. They also look to have a lot more processing power, and a free GNU-C compiler.

I'm wondering whether I should switch to ARM MCU's now rather than waste time becoming closely accustomed to PIC's, only to find down the line that they aren't powerful enough and I need to switch to something else. I had considered that using PIC chips I would probably want to break everything in to modules, each with it's own MCU. So the IMU, Data Comms, Servo Control, Sensor Arrays (airspeed, pressure altitude, temp etc) would all have their own PIC chip which would feed data back to a central flight control MCU. The problems I can see there are power consumption, weight, space and limited bandwidth for comms between processors.

I guess after all of that, my main question is, which MCU do you use in your UAV and hobby projects? Do other MCU's offer significant advantages over the PIC range?

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Do other MCU's offer significant advantages over the PIC range?

Advantages depend on what is important to the project; ease of use, support, compiler performance, time, cost, required engineer's skills, MCU features, and so on. Probably in that order, at least it is for me.

From my experience, the processor brand choice is more of a religious faith based decision than a technical one. Nearly every serious MCU manufacturer has something in their bag of tricks to be competitive. For example, to be fair, if you are looking at a ARM7, then it would be best to compare it with the PIC33F family. Still not quite the same apples-apples, but certainly a better comparison than an Arm vs. PIC16F/PIC18F.

My advice is to pick the MCU that has an affordable compiler, cheap/reliable development tools, and an extensive software library so that you don't have to keep re-inventing the wheel. A simple gauge for an entry level hobbyist type developer to find a wise choice is to determine its general popularity. More popular parts will tend to be better choices for those starting out. You can gauge this by searching around the net for user groups, forums, and published projects that use the MCU family of interest.

I would probably want to break everything in to modules, each with it's own MCU.
With the correct MCU choice you can avoid most of that and make your life much easier. If you do choose to use several collaborative MCU's in your project then you can use much lower performance parts (ie., PIC18F). Eagle Tree does this with their eLogger system, which is PIC based.
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I just got a meeting with the technical school here, and guess what they had done - an autopilot on a 30x50mm board, complete with IMU, pressure sensors, control for 3 servos, GPS, 2-way communication and many more... running on a single dsPIC33 MCU.

The dsPICs have more PWM hardware outputs indeed, but anyway until 8 servos you can easily drive them all with a single hardware PWM if you just think a bit to compensate the lack of hardware ;)

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