The HC-12 goes far beyond the typical garage-door opener RF sender and receiver boards: it is acting more like a professional transceiver, can send and receive (allowing two-way communications), and supports a wide frequency range with channels.
This module can control garage doors and remote-control devices just like the other RF modules described here. It is much more capable, though, and can serve as a programmable data transceiver.
Microprocessor-Controlled
This board uses its own microprocessor that takes care of all receiving and sending tasks. Controlling the board is very easy and does not add any overhead to your own microprocessor.
Frequency Range And Channels
The board can send and receive in a frequency range of 433.4-473.0MHz which is organized in channels with a step size of 400kHz.
Its maximum transmitting power is +20dBm/100mW, and the receiver sensitivity is excellent with -116dBm. In free line of sight, distances of over 1km can be bridged.
Both the wide frequency range and the high RF output power are incompatible with legal reguirements for free use in Europe. It is illegal to use this device without an appropriate license (i.e. radio amateur).
Specs
This breakout board by default emits 100mW which is well above the legal limit of 10mW in Europe. The RF power can be reduced by software.
| Item | Value |
|---|---|
| Voltage | 3.2-5.5V |
| Frequency | 433MHz or 315MHz |
| Output Power | 11dBm / 12.5mW |
| Sending Modes | FU1, FU2, FU3, FU4 |
| Standby Current | 3.6mA, 80uA, 16mA, 16mA |
| Sleep Current | 22uA |
| Operating Current | 100mA |
| Default Mode | FU3 at 9600bps, Channel 01 (433.4MHz) |
| Modulation Mode | AM (OOK) |
| Transmission Rate | <10 Kbps |
| Interface | UART 3.3V/5V TTL level |
| Size | 27.4x13.2x4mm |
There are two versions of this board available: one with the microcontroller STM8S003F3U6, and one with the STM8S003F3P6. These microcontrollers are identical. They differ solely in package size.
Connectors
Antenna
On the one side, the board features a through-hole connector and an IPEX connector, both to connect the antenna. The antenna solder pin is flanked by two GND pins on either side.
Always operate this device with an antenna. If no designated antenna is at hand, use a plain 17.3cm wire. Operating this device without antenna can irreversibly damage the RF unit.
Interface
On the other end, five through-holes provide the connectivity. They are clearly marked on the back side:
| Pin | Tag | Description |
|---|---|---|
| 1 | SET | Input, internal 10K pull-up |
| 2 | TXD | Output |
| 3 | RXD | Input, internal 3.3K pull-up |
| 4 | GND | negative voltage |
| 5 | VCC | +3.2-5.5V |
If the sender needs to transmit data for a lengthy time, and the power supply is >4.5V, then VCC should be reduced to no more than 4.5V, i.e. by connecting a 1N4007 diode in series to prevent over-heating.
Working Modes
The board supports the following transmission modes:
| Mode | Description | Idle Current | Serial Baud | Air Baud Rate |
|---|---|---|---|---|
| FU1 | Power Savings Mode | 3.6mA | 1200-115200 | 250kBps |
| FU2 | Super Power Savings | 80uA | 1200-4800 | 250kBps |
| FU3 | Normal | 16mA | 1200-115200 | 236kBps |
| FU4 | Ultra Long Distance | 16mA | 1200 | 500bps |
Transmission Speed
The serial baud rate controls the over the air baud rate.
| Serial baud (bps) | 1200-2400 | 4800-9600 | 19.2k-38.4k | 57.6-115.2k |
|---|---|---|---|---|
| Wireless baud (Kbps) | 5 | 15 | 58 | 236 |
Receiver Sensitivity
The faster the data transfer rate is, the lower is the receiver sensitivity:
| Serial Baud (bps) | 500 | 5k | 15k | 58k | 236-250k |
|---|---|---|---|---|---|
| Receiver Sensitivity | -124dBm | -116dBm | -111dBm | -106dBm | -100dBm |
Communication distance reduces by half for every 6dBm decrese in receiver sensitivity.
Default Working Mode
By default, the module uses transmission mode FU3: the module works at full speed, and the over the air transmission rate is adjusted to the speed of the serial port baud rate.
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(content created Apr 01, 2024)