Modules

F*CK

Sub-GHz, 2.4 GHz, Wi-Fi 6 and GNSS radios in one module: a pocket radio lab for the Kode Dot, with the pins for your code.

What it is

The F*CK module is a pocket radio lab. With it, the Kode Dot listens to and measures the radios around it and notes where each measurement was taken. It carries four radios:

• A sub-GHz transceiver for 315, 433, 868 and 915 MHz, with its antenna on the board.
• A low-level 2.4 GHz radio, with its antenna on a connector.
• An ESP32-C5 with Wi-Fi 6 on 2.4 and 5 GHz and Bluetooth, with its antenna on the other connector.
• A GNSS receiver, which gives position and time.

To see it work before writing code, install Kode Espectrum. It turns the Kode Dot into a spectrum analyser. TBD: its listing on the marketplace.

The sub-GHz transceiver, a CC1101, is driven by the P4 straight over SPI. The 2.4 GHz radio, an nRF54L15, and the ESP32-C5 run their own firmware, which the P4 loads into them over a UART. Those two do what you program into them.

How it is connected

The module comes in its own case and plugs into the header on the top edge through the interposer, which carries every line straight through. The GPIOs on this page are the header's own.

1. Screw an antenna on each connector on top of the case: a dual-band one, 2.4 and 5 GHz, on J501, and a 2.4 GHz one on J701.
2. Seat the module on the top edge of the Kode Dot. The pins enter the header and the case rests against the back.
3. Open Kode Espectrum, or your own app for the module. Kode Espectrum shows on the screen what each radio hears.

Five GPIOs go to the CC1101, four to the C5, two to the nRF54L15 and three to the I2C bus with its interrupt, all at 3.3 V. An I2C expander drives the slow lines, such as the resets and the band switch. The GNSS receiver does not reach the header: its UART ends at the C5.

"Pin" is the header's pin, the same as J401's. The direction is the Kode Dot's:

The schematic and the KiCad sources are in hardware/fck.

Specifications

The module:

The radios:

Your country's rules say what you may transmit on each band, at what power and how often. The tables say what the hardware can do.

Gotchas

Example code

To go beyond this read, the RadioLib library has a CC1101 driver. subghz_link, in the module's repository, is Kode's firmware that drives it on revision 1.0.

This example resets the CC1101 and asks it which version it is. In idf.py monitor you will see CC1101 VERSION = 0x14, what two modules answered from a Kode Dot on 2026-09-28. A 0x00 or a 0xFF means the chip does not answer.

/*
 * fck_cc1101.c - 2026-10-14 - from Kode with love
 *
 * Asks the sub-GHz transceiver of the F*CK module, a CC1101, which version
 * it is. Opens its SPI, resets it and reads its VERSION register. In the
 * monitor you will see "CC1101 VERSION = 0x14"; a 0x00 or a 0xFF means the
 * chip does not answer.
 */
#include <stdio.h>
#include "driver/spi_master.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
 
#define CC1101_SRES     0x30   /* reset command */
#define CC1101_VERSION  0xF1   /* register 0x31, read as a status register */
 
/* Sends a one- or two-byte command and returns the last byte answered. */
static uint8_t cc1101_send(spi_device_handle_t cc1101, uint8_t header, int bytes)
{
    spi_transaction_t transfer = { .length = 8 * bytes, .tx_data = { header, 0x00 },
                                   .flags = SPI_TRANS_USE_TXDATA | SPI_TRANS_USE_RXDATA };
    spi_device_transmit(cc1101, &transfer);
    return transfer.rx_data[bytes - 1];
}
 
/* Opens the module's SPI, resets the CC1101 and prints its version. */
void app_main(void)
{
    spi_bus_config_t bus = { .mosi_io_num = 14, .miso_io_num = 11, .sclk_io_num = 13,
                             .quadwp_io_num = -1, .quadhd_io_num = -1 };
    spi_device_interface_config_t chip = { .clock_speed_hz = 1000000, .spics_io_num = 19,
                                           .queue_size = 1 };
    spi_device_handle_t cc1101;
    spi_bus_initialize(SPI2_HOST, &bus, SPI_DMA_DISABLED);
    spi_bus_add_device(SPI2_HOST, &chip, &cc1101);
 
    cc1101_send(cc1101, CC1101_SRES, 1);
    vTaskDelay(pdMS_TO_TICKS(10));   /* the chip's oscillator restarts */
    printf("CC1101 VERSION = 0x%02X\n", cc1101_send(cc1101, CC1101_VERSION, 2));
}

Compiled on the date in the header with ESP-IDF v6.1. TBD: a run on a module of the issue that ships.

In the SDK

• kode.h: in a kodeOS app, kode_exp_power(true) switches the header's 3.3 V on, kode_exp_lend() takes the module's 14 positions under a name and gives you their GPIO numbers, and kode_exp_ctrl() hands you a free SPI, I2C and two UART controllers for the radios.
• TBD: drivers for the four radios in kode-sdk.
• hardware/fck: the schematic, to view and download.