Holybro Microhard Radio P900 (HT08)
Model: HT08
Product Description
The Holybro P900 Radio integrates the Microhard Pico Series P900 RF module, offering high-performance wireless serial communications. It supports robust and secure Mesh, Point to Point, or Point to Multipoint topologies. The P900 Radio operates within the 902-928 MHz ISM frequency band, utilizing frequency hopping spread spectrum (FHSS) technology for reliable wireless asynchronous data transfer between devices with a serial interface.
It can be configured as a Primary Coordinator, Secondary Coordinator, Standby Coordinator, or Remote in a Mesh Topology, or as a Master, Repeater, or Remote in a Point-to-Point (PP) or Point-to-Multipoint (PMP) Topology, providing significant user versatility. Configuration is achieved using AT commands via the Data port or the PicoConfig application through the Diagnostic Port.
Image Description: A compact black radio module with an antenna attached. It features several status LEDs (Power, Config, RX, TX, RSSI) and two ports labeled 'Power' and 'Config'. The model name 'P900' is clearly visible.
Key Features and Benefits
- USB Type-C port with integrated USB to UART converter.
- 6-position JST-GH connector, compatible with flight controller TELEM ports (e.g., Pixhawk 4).
- Onboard high voltage BEC, supporting DC12V voltage supply.
- UART transmission LED indicator.
- Three-stage RSSI LED indicator for signal strength visualization.
- Operates in a public, license-exempt radio spectrum band.
- Transparent, low latency link rates up to 276 kbps.
- Supports robust true Mesh operation with auto-routing.
- Includes 32 bits of CRC, selectable retransmission, and forward error correction.
- Features a separate diagnostics port for transparent remote diagnostics and online network control.
Specifications
| Frequency Range | ISM 902 to 928 MHz |
| Transmit Power (Software Selectable) | 4mW |
| Band Segments | Selectable via Freq. Zones |
| Link Rate | Up to 276kbps |
| Serial Baud Rate | Up to 230.4kbps asynchronous |
| Sensitivity | Low and middle data rate: 10-3 BER |
| Link Rate: 57.6 kbps, -111dBm (10-6 BER), -114dBm (10-3 BER) | |
| Link Rate: 115.2 kbps, -110 dBm (10-6 BER), -113dBm (10-3 BER) | |
| Link Rate: 172 kbps, -108dBm (10-6 BER), -111dBm (10-3 BER) | |
| Link Rate: 230 kbps, -107dBm (10-6 BER), -110dBm (10-3 BER) | |
| Link Rate: 276 kbps, -106dBm (10-6 BER), -109dBm (10-3 BER) | |
| Range | 40 miles (60km) |
| Spreading Technology | Frequency Hopping Spread Spectrum (FHSS) |
| Supported Network Topologies (Software Selectable) | Coordinator, point-to-point, point-to-multipoint, mesh |
| Error Detection | 32 bits of CRC, ARQ |
| Data Encryption | 128, 196 or 256-bit AES Encryption (Requires export permit outside US and Canada.) |
LED Status Indicators
The P900 Radio features 6 status LEDs: three blue, two orange, and one green.
- Power LED (Green): Illuminates when the P900 Radio is connected to a power source (7-35VDC).
- TX LED (Orange): Indicates when the Radio is transmitting data over the air.
- RX LED (Orange): Indicates when the Radio is synchronized and has received valid packets.
- RSSI LEDs (3x Blue): Indicate received signal strength. As strength increases, starting from the left, more LEDs illuminate. Signal strength is calculated based on the last four valid received packets with correct CRC.
| MODE | Unit Type | RX/SYNC | TX | RSSI 1,2,3 |
|---|---|---|---|---|
| COMMAND | All | OFF | OFF | OFF |
| DATA | P.Coordinator / S.Coordinator | ON while receiving valid data | ON while Transmitting data | 1-3 ON in proportion to signal strength received from remotes. |
| DATA - during sync. acquisition | S.Coordinator Remote/Standby | OFF | OFF | Cycling with 300ms ON time |
| DATA - when synchronized | S.Coordinator Remotes/Standby | ON while synced | ON when transmitting | 1-3 ON in proportion to signal strength received from Coordinator |
RSSI LED Interpretation:
| RSSI <20% | LED-20 off, LED-50 off, LED-100 off |
| 20%<RSSI<50% | LED-20 on, LED-50 off, LED-100 off |
| 50%<RSSI<80% | LED-20 on, LED-50 on, LED-100 off |
| 80%<RSSI | LED-20 on, LED-50 on, LED-100 on |
Configuration and Ports
Config Button
Holding the Config button while powering up the radio boots the unit into COMMAND mode, activating the default serial interface with settings of 9600/8/N/1.
USB Port (Type-C)
Features an internal USB to Serial Converter. Unlike the MicroHard P900 Enclosed, the Holybro P900's USB port provides direct access to the Serial data Port, allowing connection to a ground station. USB Vbus powers the USB to Serial chip only, not the radio itself.
Data Port (6-position JST-GH)
Used to connect to the telemetry port of a flight controller. When the USB Type-C port is not connected, this connector automatically links to the Serial data Port. When the USB Type-C port is plugged in, this connector is inactive. The Data Port does not power the radio.
Diagnostic Port (4-position JST-SH)
Connects to the Diagnostic Port. This port is used for configuration with the PicoConfig application or special diagnostic commands. It operates at 3.3V logic level. A USB to Serial board is required for connecting the radio to a computer via this port.
Connectivity and Settings
Power Port (4-position JST-GH)
Input voltage range is 7-35 Vdc. The radio is powered exclusively through this port. Ensure the power supply is connected during use and configuration.
Default Settings and Configuration
The default settings of the microhard P900 module may not align with flight controller telemetry settings. Holybro P900 Radios are factory-configured for Point to Point Operating Mode and 57600 Serial Baud Rate, ensuring compatibility with Pixhawk series flight controllers. After a firmware update or reset, re-configuration may be necessary.
Configuration Example using PicoConfig:
Image Description: Two screenshots of the PicoConfig application. The left shows settings for 'PP Master' with parameters like MAC Address, Product, Country Code, Mode of Operation, Network Address, Unit Address, Destination Address, Wireless Link Rate, Power, Hop Pattern, Serial Baud Rate, Serial Data Format, and Serial Channel Mode. The right shows similar settings for 'PP Remote'. Key parameters like 'Mode of Operation', 'Wireless Link Rate', and 'Serial Baud Rate' are highlighted for adjustment.
For Point to Point operating modes, a master radio is required for network synchronization. One radio should be configured as 'PP Master' and another as 'PP Remote'. Refer to the 'Pico Series P900 Operating Manual v1.8.7' for detailed radio configuration instructions.
Power Consumption
- Supply voltage: DC7~35V (via 4-position JST-GH)
- Transmit current: 200 mA/7V at 20dBm, 350mA/7V at 27dBm, 800 mA/7V at 30dBm
- Receive current: 100 mA
Weight: 42g (without antenna)
Pin Outs
USB Port
| PIN | Description |
|---|---|
| 1. VCC | Power |
| 2. RX | Receive Data |
| 3. TX | Transmit Data |
| 4. CTS | Clear to Send |
| 5. RTS | Request to Send |
| 6. GND | Ground |
Data Port
| Pin | Signal | Volt |
|---|---|---|
| 1(red) | NC | -- |
| 2(black) | RX | +3.3V |
| 3(black) | TX | +3.3V |
| 4(black) | CTS | +3.3V |
| 5(black) | RTS | +3.3V |
| 6(black) | GND | GND |
Diagnostic Port
| Pin | Signal | Volt |
|---|---|---|
| 1 | NC | -- |
| 2(black) | RX | +3.3V |
| 3(black) | TX | +3.3V |
| 4(black) | GND | GND |
Power Port
| Pin | Signal | Volt |
|---|---|---|
| 1(red) | BAT+ | 7-35V |
| 2(red) | BAT+ | 7-35V |
| 3(black) | BAT- | GND |
| 4(black) | BAT- | GND |
Dimensions
Image Description: Technical drawings showing the dimensions of the Holybro P900 Radio module in millimeters. The drawings display the length (74.1mm), width (64.6mm), height (12.1mm), and the dimensions related to the antenna connector (14.7mm) and the side port (36.6mm).
FCC Statement
This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions:
- This device may not cause harmful interference.
- This device must accept any interference received, including interference that may cause undesired operation.
This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation.
This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:
- Reorient or relocate the receiving antenna.
- Increase the separation between the equipment and receiver.
- Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
- Consult the dealer or an experienced radio/TV technician for help.
RF Exposure Information:
- The device has been evaluated to meet general RF exposure requirements.
- The device can be used in portable exposure conditions without restriction.
- This equipment should be installed and operated with a minimum distance of 20cm between the radiator and your body.
Caution: Changes or modifications not explicitly approved by the manufacturer could void the user's authority to operate this equipment.
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