WatchMeter

Just found-out about a really bad design of the SAML21 micro. In order to use it's DAC as an internal reference for the internal OpAmps I must output the DAC to it's IO pin (pin 3, in the case of DAC0). The problem is that pin 3 is shared with OpAmp0 negative input. It is then impossible to use the DAC0 AND the negative input of OpAmp0 at the same time...

So I won't be able to implement the following current source circuit with this micro.

For version 2 I will probably change the microcontroller...

- Boards just arrived from OSH Park. Still waiting the components to arrive...

Proof of concept...

• Fortunately I had a 64-TQFP breakout board for testing the microcontroller and developing the software while the main board is in production.
• I was forced to use the 64-pin version of this micro (ATSAML21J) because I was planning to use all the 3 internal OpAmps of this chip (which are all accessible only on the 64-pin version).
  • For the final version I plan to find a way to use the 32-pin version to save cost and space.

Proof of concept - Hardware

• Designed a 4 layer PCB prototype and sent to OSH Park for fabrication.
  • For a 2 layer PCB I must change the coin cell holder.