EEVblog 1538 - NEW PROJECT Part 2 - Microcontroller Selection

[EEVblog]

Part 2 in the new project desing series, selecting a microcontroller.
32 Bit Timers, Real Time Clocks, and LCD animation.

[SiliconWizard]

Biased of course, as I've used them in a number of projects over the past few years, but I would recommend the STM32L4 series.
It has everything you need and is very low power.

I'd specifically recommend the STM32L476 or L496 as they both have a segment LCD driver, a nice set of peripherals and ample memory.
If you can live with a bit less memory and fewer peripherals, you can otherwise also pick the L433 which is a bit cheaper.

[mariush]

I didn't see this mentioned in the video... .

Sometimes it makes sense to search for higher lcd "pixel" count and higher pin count chips even if you know you need a lower amount of segments.
SOME micros have the lcd fixed to specific pins which may share functionality with other stuff like SPI or DACs so for example, you could have a 64 bit micro with 80 segments but if you enable the last "channel", you lose important functionality you need, which can't be mapped to other pins.

The higher pin count may also help if you want to have backup / 2nd options for displays.
For example, may be worth thinking of just using a mass produced grayscale or color LCD that cost under 10$ but which could require a high pin count due to parallel interface

As example 320x240 rgb 2.4" for 6$ each : https://www.digikey.com/en/products/detail/orient-display/AFY240320A0-2-4N6NTN/13544636
similar displays can probably be found on lcsc or aliexpress


If you don't like marketplace products, here's one stocked at 10k+ at Digikey , this Sharp transflective 128x128 lcd : https://www.digikey.com/en/products/detail/sharp-microelectronics/LS013B7DH03/5300387
It's expensive if one is bought, but around 6$ in volume.

There's also a bigger but more expensive version with 400 x 240 resolution : https://www.digikey.com/en/products/detail/sharp-microelectronics/LS027B7DH01A/5054067

Then it's just a matter how big of a screen your product needs to have

[EEVblog]

I didn't see this mentioned in the video... .
Sometimes it makes sense to search for higher lcd "pixel" count and higher pin count chips even if you know you need a lower amount of segments.
SOME micros have the lcd fixed to specific pins which may share functionality with other stuff like SPI or DACs so for example, you could have a 64 bit micro with 80 segments but if you enable the last "channel", you lose important functionality you need, which can't be mapped to other pins.

That's part of the finer part selection and implementation details. This video wasn't about those details.

[Kleinstein]

With the automatec LCD switching one may need a version with more LCD pixel capability, just for the memory reserved for this.
I would not limit the LCD size to much - a few more pixel capable µC would not necessary be much larger / mor epower hungry. It is a more thing of a few more pins.

Designing a PCB for 2  pin counts can be tricky and require compromises with decoupling. Also the LCD mapping could be tricky. With the modern PCB tools one would still have the option to make a PCB revision for the smaller case if really needed.  A new PCB revision is no longer that bad - not need to do a dual layout with additional compromises from the start. Chances are 2 separate designs may be even easier - so why the trouble from the start, with the fall back likely never needed.

There are usually several µC versions with the same case, but difference memory levels and periphery - designing for such similar versions in the same case is often easy. A desing for the 64 K version would likely also accept (likely not even a real SW change needed) a version with more memory in the same case. So one could design with the smaller version in mind and have the larger ones as a fall back for availability of parts.   Others may however have the same idea - when the small version is out of stock, the larger ones may be gone quite fast too.

[Rdx]

I am curious about the best practices with alternative components.
Would you just place two actual components (in schematic as well as PCB view), or would it be more like a custom footprint that holds additional pads for the alternative package? How to mark the stuff so the board house knows what you expect them to do?

Guess it could be interesting when it comes to PCB design of this mystery project. Considerations and best practices. Especially nowadays with long term chip shortages.
Might make for an interesting video.

[djsb]

If you choose a PIC24 will you be doing a video on the firmware development? I'm assuming that you will be using XC16 in the MPLABX environment? Will you combine this with the MCC code configurator? I ask all this as I'm keen to learn how to learn these tools myself. Thanks.

[kurth]

I only use PIC18F parts now for the occasional 5V project. The STM32L4 line is my go-to for almost everything else. The STM32 parts are often cheaper than PIC parts, too. They have been in stock at Digikey & Mouser lately, too.

[thm_w]

Already mentioned in the youtube comments, but, I've only considered uA/MHz as a processing efficiency claim. eg the difference in current between running at 1 and 2 MHz.
The target market isnt going to buy a 32MHz processor and run it at 1MHz. They'll generally run it at 32MHz, get the processing needed done, and go back to deep sleep.

But the "always on" low power draw is definitely a market segment as well. So you could argue for another headline datasheet spec, "lowest running current" or something similar.

[VK3DRB]

Just using Digikey for supply information is not a great idea. Often Mouser will have heaps but Digikey will have none... seen this quite a few times. I suggest Findparts, Octopart or others. Also check LCSC for parts. And stay away from brokers... but they deserve to go broke (no pun intended).

Out of all the CPU and module suppliers, Microchip has a poor reputation for parts supply as well as their void communications. They burnt their bridges. Parts today, gone the next and a 52 week lead time. Forget 'em.

[VK3DRB]

Good tip on the dual footprints. Works for QFICs and SOICs, and you can have an internal BGA and an external QFIC, but keep in mind you might have transmission line issues if you have high speed external Flash or RAM driven by a high-end micro-controller.

Another thing to mention is with the dual footprints, the proximity of the supply rail decoupling capacitors should be considered if the board is single-sided. These caps should be placed as close to the VDD pins as practicable, particularly when there is a processor hammering the I/O at high speed. With a smaller footprint, 0402 caps could be placed internally to the larger do-not-fit processor, else externally if the processor is fitted. Double sided components is the nicest though if the product is not too cost-sensitive.