HC-12 433MHz Wireless Transceiver Module

The HC-12 module is a half-duplex RFRadio Frequency transceiver designed to work in the 433MHz ISMIndustrial, Scientific, and Medical radio bands band with up to 100 communication channels that have 400kHz separation, a range up to 1.8km in open air, and a UARTUniversal Asynchronous Receiver-Transmitter interface.

The HC-12 module is based on the Silicon Labs Si4463 RF chip and a STMicroelectronics STM8S003F3 8-bit microcontroller. The board usually comes with a 433MHz spring antenna to solder onto the ANT pin through hole or you can attach an external 433MHz antenna (not included) to the uFL/IPEX socket on the board.

This article covers the HC-12 module usage, specs, board layout, and modes of operation.

Usage

The HC-12 module supports 4 different modes of operation for power savings (FU1/FU2), general purpose usage (FU3), and for long range (FU4).

FU1: moderate power savings mode
FU2: extreme power savings mode
FU3: general purpose mode (default)
FU4: long-range mode (available in version 2.3 or newer)

More details on each of these modes and how to set them are in the Modes section.

Two HC-12 modules can be used in place of physical wiring, replacing a wired half-duplex serial communication link carrying TTLTransistor-Transistor Logic level signals, as shown in the figure below.

The left device (MCUMicrocontroller Unit, PCPersonal Computer, or other device) sends serial port data from its TXDTransmit Data port to the RXDReceive Data port on the HC-12 module, which automatically sends data over the air by radio waves. The right HC-12 module receives the radio signal data and restores the serial port data out the TXDTransmit Data port to the RXDReceive Data port on device to the right (MCUMicrocontroller Unit, PCPersonal Computer, or other device). Only a half-duplex link is available between the HC-12 modules, since they cannot receive and send data over the air at the same time.

Specs

HC-12 RF Module Specs
Parameter	Description
Module Info	HC-12 433MHz RF Transceiver Module (Datasheet PDF)
Transceiver IC	Silicon Labs Si4463/Si4438
MCUMicrocontroller Unit	STMicroelectronics STM8S003F3 8-bit MCUMicrocontroller Unit
Memory	Configuration setting parameters are stored in onboard non-volatile flash memory, so it will not be lost when power is removed.
Range	1.0km (in FU3 mode at 4800bps serial speed in open space) 1.8km (in FU4 mode at reduced baud rate and volume data)
Frequency	433.4MHz to 473.0MHz
Modulation	GFSKGaussian Frequency-Shift Keying modulation
Air Data Rate (bpsbits per second)	5kbps to 236kbps
Receiving Sensitivity (dBmDecibel-milliwatts (dBm) is a power level that expresses decibels in terms of milliwatts on a logarithmic scale.)	-100dBm to -117dBm (at baud rate of 5kbps in open air)
Transmitting Power (dBmDecibel-milliwatts (dBm) is a power level that expresses decibels in terms of milliwatts on a logarithmic scale.)	Configurable: -1dBm (0.8mW) to 20dBm (100mW) Default: 20dBm (100 mW)
Antenna	433MHz spring antenna pin Optional IPEX20279-001E-03 socket
I/O Data Interface	Pin Through Holes with 2.54mm (0.1in) spacing (RXReceive, TXTransmit) UARTUniversal Asynchronous Receiver-Transmitter TTLTransistor-Transistor Logic Half-Duplex, 8 data bits, no parity, 1 stop bit SET pin for configuration
Operating Supply Voltage	3.2V to 5.5V DC (minimum 200mA)
Transmitting Current	200mA (peak max), 100mA (continuous max)
Idle Current	Idle current depends on mode: 3.6mA in FU1 mode 80μA in FU2 mode 16mA in FU3 mode 16mA in FU4 mode
Operating Temperature	-40°C to +85°C
Pin Spacing	2.54mm (0.1in)
Board Size (LxWxH)	27.8mm x 14.4mm x 4mm (1.1in x 0.57in x 0.16in) (including antenna cap, excluding spring antenna)

Board Layout

The HC-12 module board layout, shown in the figure below, consists of power supply pins (VCCVoltage Collector Collector (VCC) is the supply voltage at the collector of a transistor. The double subscript notation of repeating letters "CC" is used to denote a power supply voltage that is relative to ground. and GNDCommon Ground), the Silicon Labs Si4463 RFRadio Frequency ICIntegrated Circuit, a STMicroelectronics STM8S003F3 8-bit microcontroller, an RFRadio Frequency SPDTSingle Pole Double Throw Switch chip, and external antenna (ANT) pins.

A schematic of the HC-12 board is given in the figure below. This design consists of a single antenna and two small low-pass filter sections with an RFRadio Frequency switch embedded between them to select between TXTransmit and RXReceive paths. The capacitor and inductor component values are chosen based on the frequency band.

Silicon Labs Si4463 RF Transceiver IC

The Si4463 transceiver ICIntegrated Circuit from Silicon Labs provides wireless communication in the circuit. The product page, datasheet, and application notes for this ICIntegrated Circuit can be found at the Silicon Labs website. There are many features that are not implemented in the HC-12 design, but it does offer a maximum transmit power of 20dBmDecibel-milliwatts (dBm) is a power level that expresses decibels in terms of milliwatts on a logarithmic scale. (100mW), a receiving sensitivity of -129dBmDecibel-milliwatts (dBm) is a power level that expresses decibels in terms of milliwatts on a logarithmic scale. (0.126pW), and two 64-byte RxReceive and TxTransmit FIFOFirst In First Out memories are built into the chip. The Si4463 product page has a functional block diagram shown in the figure below.

In the HC-12, the Si4463 switches between RxReceive and TxTransmit modes for the antenna and communicates any received data to the STM8S003FS MCUMicrocontroller Unit over SPISerial Peripheral Interface.

STM8S003FS Microcontroller

The STM8S003FS is an 8-bit MCUMicrocontroller Unit with the following features:

8kB of flash memory
128 bytes of EEPROMElectrically Erasable Programmable Read-Only Memory
10-bit ADCAnalog-to-Digital Converter (ADC, A/D, or A-to-D)
UARTUniversal Asynchronous Receiver-Transmitter, I2CInter-Integrated Circuit. Also referred to as IIC or I²C., and SPISerial Peripheral Interface
Multiple I/OInput/Output pins

This MCUMicrocontroller Unit is programmed to control the Si4463 transceiver and handle the UARTUniversal Asynchronous Receiver-Transmitter communication between the HC-12 and the device it is connected to.

HC-12 Pinout

The HC-12 provides a 4-pin TTLTransistor-Transistor Logic-level UARTUniversal Asynchronous Receiver-Transmitter interface (VCCVoltage Collector Collector (VCC) is the supply voltage at the collector of a transistor. The double subscript notation of repeating letters "CC" is used to denote a power supply voltage that is relative to ground. , GNDCommon Ground, TXDTransmit Data, GNDCommon Ground), with a 5th pin SET that is used to enter "command" mode for changing the module's configuration. A pin diagram is given in the figure below. The pin definitions, given in the table that follows, can be found in the HC-12 Datasheet.

HC-12 Pins
Pin	Definition	I/O Direction	Notes
1	Vcc		Power supply input, 3.2V to 5.5V DC, with load capacity not less 200mA. Note: if the module is in the transmitting state for an extended time, it is suggested that a 1N4007 diode be connected in series if the supply voltage is greater than 4.5V, to avoid overheating the onboard LDOLow Dropout Regulator regulator.
2	GND		Common ground
3	RXD	Input (weak pullup)	UARTUniversal Asynchronous Receiver-Transmitter data input, TTLTransistor-Transistor Logic level. There is a 1kΩ resistor connected in series inside the module.
4	TXD	Output	UARTUniversal Asynchronous Receiver-Transmitter data output, TTLTransistor-Transistor Logic level. There is a 1kΩ resistor connected in series inside the module.
5	SET	Input (10kΩ pullup)	Parameter setting control pin, active low level. There is a 1kΩ resistor connected in series inside the module.
6	ANT	Input/Output	433MHz antenna pin
7	GND		Common ground
8	GND		Common ground
9	NC		No connection, used in mechanical fixing, compatible with HC-11 module pin position
ANT1	ANT		IPEX20279-001E-03 antenna socket
ANT2	ANT		433MHz spring antenna solder eyelet

Modes

The different operation modes of the HC-12 given in the table below can be found in the HC-12 Datasheet.

HC-12 Modes
Mode	Idle Current	Baud Rates (bpsbits per second)	Notes
FU1	3.6mA	1200bps, 2400bps, 4800bps, 9600bps, 19,200bps, 38,400bps, 57,600bps, or 115,200bps	Moderate power saving mode. In air baud rate is 250,000 bps.
FU2	80μA	1200bps, 2400bps, 4800bps	Power saving mode. In air baud rate is 250,000bps. It is recommended that the sending time interval between data packets is no less than 1 second.
FU3	16mA	9600bps	Default. General purpose mode.
FU4	16mA	1200bps	Useful for maximum range, up to 1.8km. In air baud rate is reduced to 500bps for improved communication distance. Each packet should be 60 bytes or less. It is recommended that the sending time interval between data packets is no less than 2 seconds to prevent data loss.

The HC-12 module makes use of ATShort text string commands where the AT stands for ATtention and every command line starts with "AT" or "at". commands, like those used on old modems, on the SET pin in order to change the mode from the factory default FU3 mode to a new mode.

To enter the command mode, power on the board and then pull pin 5 (SET) low and wait 40ms for the command mode to engage. Pin 5 has a 10kΩ pullup resistor connected internally, allowing the pin to be driven by an open-collector output from an attached device like a MCUMicrocontroller Unit or USB Serial Adapter device.

To exit the command mode, you can either release pin 5 or set it high and wait 80ms. Once the mode is set, the changes will be applied after exiting from the command mode with the new parameters stored in onboard non-volatile flash memory in the MCUMicrocontroller Unit, so it will not be lost when power is removed.

The following table gives ATShort text string commands where the AT stands for ATtention and every command line starts with "AT" or "at". commands found in the HC-12 Datasheet.

HC-12 AT Commands
Commands	Notes
AT	After sending command "AT" to the module, the module returns "OK".
AT+Bxxxx	Sets the serial port baud rate.
AT+Cxxx	Sets the wireless communication channel.
AT+FUx	Sets the model of the module.
AT+Px	Sets the transmitting power of the module.
AT+Udps	Set data bits (d), parity (p), and stop bits (s) for serial port communication.
AT+SLEEP	Sets module in sleep mode operating at 22μA. This mode does not allow serial port transmission. When entering the command mode again, the module will exit from sleep mode automatically.
AT+DEFAULT	Sets configuration to default factory values.
AT+Ry	Receive single parameter from module. y can be B, C, F, and P. "AT+RB": baud rate "AT+RC": communication channels "AT+RF": mode FU1 to FU4 "AT+RP": transmitting power
AT+RX	Receive all parameters from module.
AT+V	Receive firmware version info from module.
AT+UPDATE	Puts module state waiting for software update.

References

A summary of the references used in this article are listed in the table below.

References
Reference	Link
HC-12 Module Datasheet	Elecrow.com
Si4463 RF Transceiver IC Product Page	Silabs.com
Si4463 RF Transceiver IC Datasheet	Silabs.com
Si4463 RF Transceiver IC Application Notes	Silabs.com
Comparison between the Si4463 and Si4438 RF Transceiver ICs	IoT-RF.com
STM8S003F3 MCU Product Page	ST.com
STM8S003F3 MCU Datasheet	ST.com
uPG2214TB IC SPDT RF Switch Datasheet	Mouser.com

Resources

A summary of resources to explore this topic further are listed in the table below.

Resources
Title	Description	Links
Which radio module? NRF24, LoRa, CC1101, HC12, 433MHz, HC05	YouTube video by Electronoobs. Shows examples and usage for the following RF modules: NRF24, LoRa, CC1101, HC12, 433MHz, HC05	YouTube.com
HC-12 FIX for bad clones	YouTube video by DIY Tech Bros. Shows how you can fix bad HC-12 clones that have no range. Turns out, it is usually only an error on the PCB that you can fix with some solder.	YouTube.com
2 KM SUCCESS STORY with HC-12 - going beyond 1800 meters!	YouTube video by DIY Tech Bros. Achieved a range of over 2 km with the HC-12 module.	YouTube.com