10 years ago.

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10 years, 7 months ago.

Hey there. This is my experience with LPC1768 (Cortex M3) vs STM32F103 (Cortex M3) vs PICAXE (PIC18F) vs Arduino AVR (AVR) vs Teensy 3.1 (Cortex M4).

Arduino AVR is an 8-bit architecture. Whilst fine for low powered applications and most hobbyist projects, computationally intensive applications are very lacking in terms of mathematical ability. Furthermore, the processor is slow. Advantage is that Arduino code is so readily available, and uploading programs is very easy.

I then upgraded to a PICAXE and dabbled with PICs. They are great processors. Actually faster compared to Arduino AVRs, and has more code space. Power consumption is lower compared to an equivalent AVR. Size of a PIC can be a lot smaller too. Programming is a bit more challenging, depending on the environment. I worked with a BASIC IDE, and so I found the PICs unsatisfying. However, if you set up a C environment, I would prefer a PIC over Arduino any day; for the larger code space and better number-crunching power.

Now enter the ARM Cortex M3 architecture. The M4 architecture, found in a Teensy 3.1, is actually an M3 PLUS extra features, primarily a floating point processor. That is to say, M4 = M3 core + M0 core built into the one chip.

I love Cortex M3 chips! Their mathematics ability is amazing; from a computer systems perspective, the number of instructions executed per second is unbelievable. Example? Quadcopters are now merging over to the 32-bit architecture of these Cortex chips. Not to mention, there are a tonne of ports available: PIO, I2C, USART/UART, SPI, ADC, DAC etc etc.

So which company/processor implementation of the Cortex M3 chip? LPC1768 by NXP, STM32F by ST Micro, or MK series from Freescale?

My 3 choices these days are the abovementioned 3, depending on how much money is in my pocket.

My top choice: I like the MK series (found on a Teensy 3.1) because it is an M4 architecture. Most of the stuff I do is calculations of AHRS, sampling and PID control. I prefer working in engineering units and this means floating point maths. The chip has more than adequate speed, and is found on a very small package. It is also pretty cheap, at $20 per pop for a complete dev board. Furthermore, depending on how you work, the Teensy works with Arduino and its library is under constant dev by the creator.

Next choice: STM32F. These are so cheap!!! Hop onto ebay, or source straight from the manufacturer, these chips are cheap as chips! They offer a large amount of PIOs and busses. Depending on your budget, you can get variable memory. However, their timer is 16-bit, but there are more DACs @ higher precision (2x12-bit). Problem is setting up a free toolchain to make this chip work is in my opinion, PITA. If you are fortunate to have access to Keil, then the STM32F can be programmed very nicely (rich in features), but overall programming this chip is harder than need be. Such is the price to pay for power in such a small and cheap package. If you are interested the ST chips have true SD card interfacing over SPI.

Final choice: LPC1768. These aren't the cheapest chips to get. In the area I live, sourcing these can be a challenge. However, I would be more than happy to wait and pay more than the above 2 for one reason: 32-bit timer. Even if the LPC1768 only has 1x10-bit DAC, I love the 32-bit timers because my applications are time critical. Why else would I use this chip? The mbed platform. Enough said.

I hope my answer is enlightening and helpful, in spite of my ramble.

Regards, Ian