I2C Interface in H2 M
Although the official documentation states that only PortaPack H4 or M variants support I²C communication, it is technically possible to enable this functionality on PortaPack H2 and H2+ as well.
This guide describes a simple hardware modification that enables I²C communication on H2/H2+ by internally wiring existing HackRF One signals to the ESP32 inside the PortaPack.
The HackRF One already provides an I²C interface (I2C0) through its expansion header. PortaPack H4 and M expose these I²C signals as part of their extended GPIO headers — allowing the ESP32 on board to communicate with the HackRF over I²C with an external interface (GPIO mod).
However, PortaPack H2 and H2+ do not connect these signals to an external port. They receive the same interface from the HackRF, but the I²C lines (we're insterested in SCL and SDA) are left exposed from inside the PortaPack to external GPIO port.
By adding just two wires inside the PortaPack H2 or H2+, you can route these existing I²C lines from the HackRF to the ESP32, replicating the hardware behavior of the H4/M.
This mod does not require opening or modifying the HackRF One itself — the wiring is entirely inside the PortaPack.
For more details on the ESP32’s role and pin assignments, see the official guide:
Build your module (Wiki)
The PortaPack H4 exposes its GPIOs through a 12-pin connector, physically accessible from outside.
This connector includes both I²C lines:
| Pin | Label (Top Row) | Description |
|---|---|---|
| 1 | GND | Ground |
| 2 | VBAT | Battery voltage |
| 3 | SCL | I²C Clock (I2C0_SCL) |
| 4 | SDA | I²C Data (I2C0_SDA) |
| 5 | V3.3 | 3.3V |
| 6 | VCOIN | Coin cell power |
| Pin | Label (Bottom Row) | Description |
|---|---|---|
| 7 | VCOIN | Coin cell power |
| 8 | V3.3 | 3.3V |
| 9 | SDA | I²C Data (I2C0_SDA) |
| 10 | SCL | I²C Clock (I2C0_SCL) |
| 11 | VBAT | Battery voltage |
| 12 | GND | Ground |
Notice that the bottom row mirrors the top row in reverse order, and some vol. wires never are used.
This GPIO header is not present on PortaPack H2 or H2+, but the internal signals are still routed from the HackRF expansion interface. The mod simply replicates this physical connectivity inside the H2/H2+ by wiring to the same I²C lines.
Source: Build your module - Wiki
- PortaPack H2 or H2+ with HackRF One
- Soldering iron with a fine tip
- Two short wires
- FLUX, always use FLUX when use a soldering iron
Carefully disassemble the PortaPack H2 or H2+ unit to access its PCB. You do not need to open the HackRF One.
On the PortaPack’s edge connector (which mates with the HackRF), locate the pads corresponding to:
| Signal | Label on HackRF (P22) | Description |
|---|---|---|
| SCL | Pin 24 – I2C0_SCL | I²C Clock |
| SDA | Pin 26 – I2C0_SDA | I²C Data |
These signals come from the HackRF expansion port but are not connected internally in H2/H2+.
Solder two short wires from the PortaPack expansion pads for SCL and SDA to the corresponding ESP32 GPIO pins configured for I²C clock and data in your firmware.
Also, use FLUX, to extract the 3.3v and GND:
If you want the battery and the coin voltage (I don't recommend it) you simply solder a wire to the + connector of the coin and lithium battery.
For more information related to this mod, use the Build your module guide to identify which ESP32 pins are used in your build.
Important: You are not modifying the HackRF itself — only wiring existing signals inside the PortaPack.
No firmware changes are required.
The ESP32 inside the PortaPack is configured as an I²C slave using only the SCL and SDA lines, with default I²C address 0x51.
From the firmware source (main.cpp):
PPHandler::init((gpio_num_t)CONFIG_I2C_SLAVE_SCL_IO, (gpio_num_t)CONFIG_I2C_SLAVE_SDA_IO, 0x51);Once wired correctly, the PortaPack H2/H2+ will communicate over I²C just like the H4/M models.
This modification was proposed and discussed in the community at:
It has been verified by schematic inspection and code review as electrically compatible.