v2.0 Prototypes:

I sent Claude to canvas the available collection of hobbyist model rocket flight recorders and make recommendations for upgraded features. He came back with two suggestions:

1. Integrate the USB interface with a controller that doesn't require Windoze to install a special driver. This would spare the user additional expense of purchasing the CP2102 adapter and the custom wire harness. A simple USB type-C terminated cable is all that is required to connect and download flight data.
2. Add a (PRO) version that will allow the user to record multiple flights without having to connect a USB port for downloading data.
3. Increase the baud rate of the USB connection from 9600 to 76800. This will reduce the time required to download multiple flight data.

With these upgrades the Payload would be competitive with all of the sub-$125 offerings: Many don't include an accelerometer. None of them offer an exhaustive multi-OS interface -- usually one or two at most -- and some don't offer downloading data. Many require the user to purchase an external battery charging module at additional cost. As far as I can tell, the only feature this Payload lacks is a Bluetooth connection primarily for interfacing to an iPhone.

v2 changes from v1:

• Added the MCP2221a USB-UART "Protocol Converter" to eliminate the outboard CP2102 adapter. The MCP2221a doesn't require a special windows driver installation, which is a plus, but time will tell. The MCP2221a requires its own 3V3 LDO (another XC6206) -- it only regulates the supply for the USB signals so the UART outputs have 5V logic levels, which would overdrive the PIC. There is a USB connector mounted on the back side of the PCB. It is compatible with USB 2.0 -- requiring a 16-pin connector.
• Figuring out how to program the PIC was a challenge. There is no room on the PCB for any kind of pin header, or even POGO pins. I eventually figured out that I could use the USB connector interface to program the PIC by inserting a SPDT analog switch. The switch routes VDD (3V3) and MCLR to the USB connector when VBUS is not present (0V). Otherwise (when VBUS=5V) those pins are connected to D+/D- between the USB connector and the MCP2221a. The PIC programming pins, ICSPDAT/ICSPCLK, are dedicated to the CC1/CC2 pins of the USB connector. During normal operation CC1/CC2 just have a 5.1k resistor connected to GND, which is a low voltage. As of right now this concept has not been tested.
• I recently discovered the ST LPS22HB pressure sensor. It has an identical pinout/footprint to the Bosch series of pressure sensors (BMP390, BMP384, BMP388). The advantage is that the LPS part calculates temp compensated pressure, which avoids having the PIC perform that task without floating point math. It also is stocked in large quantities (~10k) at JLCPCB/LCSB and I can get prototype quantities from Digikey.
• Added a battery monitor feature. The App will display battery voltage as it is being charged. There is also an LED indicator. The plan is to warn the user when the battery drops below 3.5V as he arms the Payload for a flight.
• The PRO version will have a 4Mb EEPROM and be able to store 8 flights (maybe more.) As of now, each flight will occupy 512kb of memory. If the user doesn't download the flights before the 8th flight, the oldest flight gets overwritten. The flight count is indicated when the payload is armed -- every 5 seconds the current flight count is beeped out by the buzzer as a rapid burst.
• The PCB was upgraded to 4-layer. It is still the same dimensions as v1 -- 12.48mm x 29.35mm. Most of the passive components were changed to 0402 size (which are a PITA to solder.)

All of this was incorporated into the same dimension PCB: