How do engineers pick microcontrollers for a project?
In this article, we will talk about how engineers pick microcontrollers for a project.
For a commercial project, you try to get the cheapest part you can use that will meet all the requirements of your project, making sure it is available in the quantities you need. That is the reason that there are still three times as many 8-bit microcontrollers sold each year as 32-bit ones; the cheapest 8-bit ones are under 30 cents in quantity, whereas the cheapest 32-bit ones are twice that. And those are Digi-Key distributor pricing; a high volume manufacturer will be able to negotiate much better prices, perhaps half of these amounts. Every penny counts in high volume.
What are the requirements? You need to look at:
- Size of the program (Flash) and memory (less than 1KB, all the way up to 2 MB or more).
- Size of data memory, i.e. RAM (16 bytes up to 512 KB or even more).
- Preferred data bus size (are you doing especially 8, 16, or 32-bit math? do you need hardware floating point?).
- Speed (1 MHz up to 1 GHz).
- EEPROM (if any, usually just a few KB).
- A number of timers.
- Peripherals needed and a number of each (I2C, SPI, I2S, UART, USB, CAN, Ethernet, ADC, DAC, DMA, PMP, CRC, WDT, etc.).
- Number of GPIOs (general-purpose I/O pins).
- A number of pins in the package.
- Package type (through-hole, or dozens of the styles of surface mount).
- Any other special features (very low power, DSP, crypto, external memory interface, etc.).
- Voltage (3.3v or 5v for example).
So, before you can even begin to look around, you need to have a handle on all of that. Then you can use a selection guide to narrow your choices, and matching your requirements to the best price.
Once you’ve narrowed your choice, you want to make sure the part is readily available, preferably from more than one source, and is not likely to go obsolete in the near future.
Often, this will not be your first project, so the tendency will be to go with parts that are identical to ones you have already used, say the Microchip PIC line. The advantage here is that you can often programming devices you have used in the past and/or use the same development tools.
If you are at the beginning of a project, and not quite sure of your needs, then the best approach is to get a development board with a microcontroller with importantly more than your estimated Flash and data memory requirements; once you have most of your program finished you might be able to fit it into a smaller microcontroller in the same family, so you will not have to rewrite any firmware but you can get by with a cheaper price in production.
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