Here we will describe the necessary pieces of hardware needed to connect to the Locha Mesh, using a DIY version of the Turpial as an example.
A Turpial consist of a MCU with a integrated radio transceiver CC1312R, a WiFi module ESP32 and some complementary circuits such as USB to Serial converter, power amplifier (PA) for the radio transceiver, power source and battery charger and some LEDs for a visual interpretation of the system status.
The basis of the entire system is the CC1312R, a small MCU with radio transceiver for Sub-GHz frequencies and a PA for TX output power up to +14dBm.
Not many manufacturers are integrating the MCU described above, only the italian Radiocontrolli creates modules and kits for development.
Texas Instruments (TI) develops a ready-to-use development kit named LAUNCXL-CC1312R1 with debugger, MCU, and power supply. This was our development platform for months previous to the first Turpial board.
Other compatible modules are CC1352R, CC1352P, both of TI and AT86RF2xx family (not yet tested) from Microchip.
The assembly will depend on if we want a simple-client or multi-client system, for those we'll need:
A dev-kit as above described connected via USB port of our PC or credit card sized computer like a Raspberry PI or similar.
The USB port provides connectivity and power source for the board so this is the simplest setup, only flash the firmware following the instructions in btcven/radio-firmware.
We'll need:
-
LAUNCHXL-CC1312R1 or compatible dev-kit with the latest firmware available in our radio-firmware repository.
-
ESP32 dev board such as WROVER-KIT-VB with the latest firmware available in the turpial-firmware repository.
We recommend to follow the instructions carefully for flashing the firmware and initial setup in each repository.
A simplified blocks schema of our DIY Turpial:
In our case the USB to Serial converter and the CC1312R MCU are on the Launchpad, and between this and the WROVER dev-kit we need to connect only two wires for the UART interface and GND for a common ground reference.
| LAUNCHPAD-CC1312R1 | WROVER DEV-KIT |
|---|---|
| DIO11 | GPIO22 |
| DIO12 | GPIO21 |
| GND | GND |
At first, any ESP32 board can work, just make sure to follow the next recommendations:
- Use only the UART1 in the ESP32 to connect to CC1312R dev-board or module.
- The UART0 is reserved to connect USB to Serial converter in most of dev-boards for debugging purposes and bootloading.
- Currently, the ESP32-S2 is not supported.
The list of ESP32 boards available in the market is huge, for example:
| Board Name | UART1 TX/RX | Manufacturer | Observations |
|---|---|---|---|
| HUZZAH32 - ESP32 Feather | 17/16 | Adafruit | LiPo Battery charger |
| WiFi KIT 32 | --- | Heltec | LiPo Battery charger, OLED display |
| TTGO T7 V1.3 MINI 32 | 1/3 | Lilygo | Battery charger, small factor |
| Thing Plus - ESP32 WROOM | 17/16 | SparkFun | Battery charger |
| ESP32 NodeMCU (various models) | N/A | Several | Cheap |
| Wemos (various models) | N/A | Several | Cheap |
We can use the USB connection in each board as power source or in some models a power management system is available, including battery charger, but keep in mind not all ESP32 based boards can be used as power source for the CC1312R, check the output current that each board can offer.
In case you need more power you can add a battery manager and power source in the system like the "Babysitter" from SparkFun, it can monitor the battery status and current drain in real time using the I2C interface.
Connect the Babysitter as follows:
| LAUNCHPAD-CC1312R1 | Babysitter | WROVER DEV-KIT |
|---|---|---|
| DIO4 | SDA | N/A |
| DIO5 | SCL | N/A |
| DIO8 | GPOUT | N/A |
| GND | GND | GND |
| 3V3 | VPU | N/A |
| 3V3 | VOUT + | 3V3 |
| GND | VOUT - | GND |
You can use a 1000mAh battery or greater, LiPo type, 18650, etc., or without battery by using the charging port connected to a power bank or a computer's USB port.
In this tutorial we have described how to make a DIY version of the Turpial device, including different approaches depending on your goal, budget or skills.
The Turpial custom hardware we have designed includes everything mentioned above in a portable form plus a power amplifier, and other elements which improve the performance of the system. You can buy a Locha Mesh Turpial here.