Spearmintastic!

Self-sufficient, pocket sized

Spearmintastic is a pocket-sized device designed for use as Meshtastic node. Unlike most other tiny node designs, it is designed to be fully self sufficient (including battery, solar panel, and LoRa antenna) in a footprint no larger than its 21x71mm PCB.

Spearmintastic uses a "14500" (AA) size protected Li-ion battery, minimizing fears about sketchy pouch cells from Amazon or AliExpress. These can be found via online retailers as "flashlight batteries".

Errata Notes:

• Solar polarity silkscreen is reversed on v1.0 board
• Protected 14500 lithium cells tend to be a couple millimeters longer than a "normal" AA battery. You may need to do some modifications to the Keystone holder to make the battery fit well. If needed, recommended modifications are to flatten the contact springs with a pair of pliers, as well as cutting some of the plastic "backstop" out from behind the positive contact to allow it more travel.

Bill Of Materials

Part	Spec	Qty	Link
PCB	Spearmintastic v1.0	1	This repository!
Microcontroller	Seeed Studio XIAO nRF52840	1	DigiKey
LoRa Radio	Ai-Thinker Ra-01SH or Heltec HT-RA62	1	Ra-01SH or HT-RA62
Solar Charger	SD05CRMA (CN3163 Breakout)	1	AliExpress
Antenna	Pulse W3139	1	DigiKey
Solar Panel	ANYSOLAR SM141K09L	1	DigiKey
Solar Panel Pigtail	2x wire, 1.25mm PicoBlade termination	1	DigiKey
Solar Panel Connector	2 position 1.25mm PicoBlade, vertical THT	1	DigiKey
Solar Overvoltage Shunt	6.2V Zener Diode (SOD123 package)	1	DigiKey
Bulk Capacitor	10uF MLCC capacitor (1206 package)	1	DigiKey
Battery Holder	Keystone 1024 (see note)	1	DigiKey
Battery	14500 size Li-Ion cell (protected)	1	B&H Photo
Case (optional)	Spearmintastic case	1	Your 3D printer (files on this repo)

Case

A 3D printable case has been designed to fit a fully assembled Spearmintastic, with battery and panel. A cutout is provided for access to the Xiao's USB-C port.

Firmware

Pre-built firmware coming soon?

Meshtastic built for the "xiao_ble" target should be directly compatible with Spearmintastic, however in my testing, the battery voltage indication does not work. This can be fixed by adding the following to the variant.cpp file:

void initVariant() {
    pinMode(BAT_READ, OUTPUT);
    digitalWrite(BAT_READ, LOW);
}

This is not an issue specific to Spearmintastic, as the voltage monitoring circuit is built onto the Xiao.

License

Spearmintastic is licensed under the CERN OHL v2 Permissive license. See the LICENSE file for more information.