Question about choice of microcontroller (and about Raspberry Pi Pico as alternative)

[msgilligan]

Why was the SparkFun Thing Plus - SAMD51 chosen? Is there any public documentation about the reasons for this choice?

Would it be possible to build the LetheKit with the $4 Raspberry Pi Pico? If not, why?

I'm asking for two reasons:

1. To better understand the current design decisions
2. I'm tempted to try to see if I can port this to the RP2040/Pico

[gorazdko]

Why was the SparkFun Thing Plus - SAMD51 chosen? Is there any public documentation about the reasons for this choice?

I don't know about the reasons, @ksedgwic is the original author who came up with the setup. @ksedgwic can you comment on that?

Would it be possible to build the LetheKit with the $4 Raspberry Pi Pico? If not, why?

This could be doable if you stay within Arduino environment, otherwise I dont think it will be that easy.

Note also that lethekit uses cortex m4 whereas rpi uses m0+, so some compiling difficulties will arise from that. And wrt to resources (gpios, RAM, peripherals, idk about TRNG?) I'd say the rpi should handle it.

[ksedgwic]

@msgilligan We were looking for an Arduino compatible device that didn't have radios (Bluetooth, WiFi, ..)

[ksedgwic]

I'm not a fan of the TRNG part anyway, I think all the entropy should be generated with dice. Everything else is very portable ...

[msgilligan]

Thanks for the responses, @gorazdko and @ksedgwic!

The Pico doesn't have any radios, either. So it should be a good choice if it can be made to work. ($16 cheaper)

I've ordered the SAMD51 and the other major components and will try to build one. I'm experimenting with the Pico on another project. I may try to see if I can get the code to run on the Pico. I believe the Pico works with the Arduino environment, so it might not be that difficult.

[ksedgwic]

A big component of the price of the Thing Plus is the battery charging circuit. If you can live w/o the battery things can be significantly cheaper. Alternatively, if there was sufficient interest (quantity) it would make sense to design a PC board with the charging circuit provided externally. A PC board would also simplify the assembly and make the result much more rugged ....

[msgilligan]

So with the Pico, you'd have to use a power adapter or a disposable battery pack?

There is also this board available: https://www.sparkfun.com/products/17745 (currently out of stock)

[gorazdko]

So with the Pico, you'd have to use a power adapter or a disposable battery pack

yes. You could also use rechargable batteries but you won't be able to recharge them via the board's usb

There is also this board available

this one supports charging, but it's also more expensive