Here’s what the first week of development looks like to build an open source function generator in time for for OSHWA 2020. Each day’s entry represents an hour’s work per day - the hour before I leave for my job every morning, to be precise.

Feb 7 2020

Initial placement underway!
- Like the cross-association between layout and schematics in KiCAD.
- Highlight a component in EESchema, and it will be highlighted/selected in PCBNew
- Kind of hard to do on my Macbook. I wish I had a second monitor.
- Wish there was a way to select a cmpt, then hit a button that was like “Jump to Layout Editor” - I always seem to select a component in EESchema, then click into PCBNew, and find it’s been de-highlighted.
Deleted the secondary LDO
- Not really using any analog functions of my MCU
- Could use it as aux power to the DDS, but that’d mean a long power route somewhere that I don’t really want to futz with.
Starting to think about test point placement
- Kerry Scharfglass’s Hackaday video got me thinking about testpoints = fixtures = time saved
- Hi Kerry! Thanks for answering my email.

Feb 6 2020

Make LFCSP-10 footprint for AD9837
- No need! I was searching for the wrong footprint in the default library. Looking for LFCSP-WD package found it. It was already there! And a check in the footprint editor showed the dimensions matched.
Finish assigning footprints
- This is more nerve-racking than I expected. Constant thought: “What if I fuck one up?” Instant empathy for team of PCB designers at work.
- SeikoEpson - your recommended footprint pattern for SG5032 oscillators calls out the wrong part number! WHY!!!
Find the right footprint for the crystal (not the oscillator)

Replaced LDOs with MIC5504 (much cheaper!)
Added missing power net for 3.3V rail to DDS oscillator
Assign RefDes’es
- Done! Easy!
Make layout floorplan!!
Assign footprints
- Wow, this takes a long time, and is anxiety ridden.
Added breadboard headers for mounting (that’s the whole point of this fucking thing!!)
- Would make a whole lot more sense if they connected to something though

Broke SCH into hierarchical components. Never done a design this way before - we’ll see how this goes!
Implemented STM32F072C8T7 Reference Design
~~Add TVS for USB~~
- I didn’t do this, and may end up regretting it. Note to self - buy a ground strap.
Add JTAG connector for MCU!
- Done - went with SWD connection. Compatible with ST-Link, or that Segger I have kicking around in my box of random debugger crap.

Make symbol for AD9837
- This is easy, and pretty intuitive
- The symbols are the reverse of what I’m used to (orcad) - bubble is the connection point for the wire, not for the symbol box
- I like that you can automagically include the datasheet link and part information
- Also really enjoying the hot keying setup - just hit a button and you bring up a new dialog
- Also - how do you make the interior of the SCH symbol yellow like everything else?
Start reference design of AD9837
- Issue number 1: what’s the primary power source of this thing?
- Lots of jumper options for selecting power into the device
- Do I gather from the reference design that the AD9837 is supposed to be powered by its own POL, and everything else has a separate POL? If so, I’ll definitely be finding a cheaper LDO.
- Packaged oscillators. Convenience = yay! Price = woof. $1.10 per piece.
Hierarchical design!
- That’s very cool, and a really different design paradigm than I’m used to.
- See a lot of advantages to it - easily replicate circuit “chunks”
- Is it as easy to do in layout as it is in SCH? Do you get layout rooms by default as well?

Start SCH capture of ATSAMD21 MCU
- Use Datasheet Section 42 (SCH Checklist) as guideline for SCH capture
  - Note to MFGs: this is a great way to get HW engineers to use your parts
  - It’s also a shitload cheaper and more scalable than hiring a bunch of FAEs - paper scales, people don’t!
  - Have a step-by-step guide saying “This is how to implement this thing in HW”
  - We’re typically some combination of time-crunched, and lazy
  - Brilliant!
- http://ww1.microchip.com/downloads/en/DeviceDoc/SAMD21-Family-DataSheet-DS40001882D.pdf
Need to Find 5.0V -> 3.3V LDO
- Added NCV8114ASN330T1G from On Semi (was in KiCAD’s design library)
- Could probably find something cheaper though

Still mostly parts research at this point.

ATSAMD21
- Only capable of 3.3V IO voltages, so that kind of dictates what everything else must run at.
AD9837
- Voltage out only - no need for 200 ohm resistor to terminate current driver.
- No comparator output - square wave achieved by driving MSB of phase accumulator at the VOUT pin.