The Desk of Ladyada - Yaaar Matey, a Circuit Pyrate Prototype!
72This week at my desk, we have Pyrate Protos - our RP2040 respin on the 'bus pirate' design is here, and a few things worked & a few things didn't. Still, we were able to verify a bunch of the hardware. the toughest part is how to replicate the 5V-compliant inputs of the original. we wanted to get this design out the door so we threw on our basic '3.6V zener plus 1K resistor' protection circuit that we use on many of our Stemma-having boards. however, it works poorly with the light 10K pullups on the PCB because the zener isn't biased with enough current. we found, sorta by accident, a comment by Eben Upton from Raspberry Pi that noted the RP2040 actually is 5V compliant, just not 5.5V compliant (https://hackaday.com/2022/09/25/pi-pico-w-does-pcmcia-gets-this-ibm-pc110-online/#comment-6516402) which makes us rethink how we may want to do the protection. this app note (https://ww1.microchip.com/downloads/en/DeviceDoc/chapter%208.pdf) has lots of great ideas. while we re-spin the board we put together a quick arduino test sketch that performs a self-test on the hardware.
The Great Search - Zener Diodes
https://www.digikey.com/short/q0nb98jq
Zener diodes (https://blog.adafruit.com/2013/07/17/your-moment-of-zener/) really are amazing little devices, useful for a dozen different circuits. (https://www.evilmadscientist.com/2012/basics-introduction-to-zener-diodes/) We like to use a Zener clamp (https://ww1.microchip.com/downloads/en/DeviceDoc/chapter%208.pdf) as a basic method of protecting analog inputs on some of our dev boards so you can plug 5V in by accident and nothing bad will happen to the chip GPIO. They're available in just about every voltage setting - let's check out some tips on using Zeners, (https://www.onsemi.com/pub/Collateral/HBD854-D.PDF) what to watch out for when specifying them and all the different packages available at DigiKey. Also, we'll check out DigiKey's new branding, released this week!
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