What is it?

10mbps over 1km on a single pair of wires* (1km is not tested, only theoretical).

μDiff provides an easy way to reliably transfer power and a digital signal over a long-distance using an inexpensive RJ-45 cable.

It uses RS-485 differential signaling and 802.3af mode B pinouts to achieve this. The μDiff module can accept an input voltage between 8V-28V, and provides outputs of 5V and 3.3V. Both output voltages, GND, along with the RO, RE, DI, RE signals can be accessed through an 8-pin header.

Current is limited to 1A with the default components, but can be upgraded to ~2A with a different 5V switching regulator and fuse. Beware of current limitations on the RJ-45 cable, it's typically ~700mA for an AWG26 shielded wire pair (2 wires).

Some components are pre-soldered SMD (0805), while the rest are easy to source off-the-shelf through-hole components.

The board measures 50mm x 44mm, lead-free and RoHS compliant, and is designed to be stackable through 4 grounded M3 holes.

This project is certified open hardware:

Why did you make it?

I don't always want to use wireless signals to transfer data over a long distance. For reliability or simplicity's sake, an RJ45 cable can do wonders to connect multiple devices. Unfortunately I couldn't find anything to reliably control small devices and LEDs over a +15meter distance, so I designed this module to make that possible.

What makes it special?

Each connected module can safely power 3.3V and 5V devices all from a single power source (ex: 12V wall wart).

What's included in the kit?

One full kit (PCB and through-hole components for 1 module) ships with the following components, orders for a pair contain double the components listed below:

• PCB with some pre-soldered SMD components
• 2-pin terminal block
• 8-pin 2.54mm header
• 3-pin 2.54mm header
• Jumper
• 900mA resettable poly fuse
• 120 ohm terminating resistor
• RJ45/8P8C connector
• 2 position dip switch
• 8-pin DIP socket
• 8-pin MAX3088 RS-485 IC
• 5V DC-DC voltage regulator
• Printed schematic, soldering diagram, and wiring diagram

What's not included?

The kit does not supply a JST-XH connector, RJ45 cable, mounting screws, tools, wires, or anything not listed above.

Other remarks

Although the PCB is designed to hold an 8-pin JST-XH connector, I realized many people would rather use simple 2.54mm pin headers instead. The kit will not ship with a JST-XH connector but you're free to use one if you prefer.

Safety remarks

The 3-pin VIN/RJ-45 header connects the VIN and RJ-45 pins through a jumper. This is somewhat dangerous and shouldn't be touched on a powered circuit.

The onboard capacitors are quite small and should discharge automatically, but it's still a good idea to always disconnect power before disconnecting the LEDs or MCUs.

Do not feed power into the 8-pin header (3.3V or 5V pins). Those are output pins and could damage the voltage regulators.

Do not connect anything other than a μDiff module to the RJ45 cable. Although it uses standard 802.3af mode B pinouts, similar to passive PoE devices, it is not PoE (Power-over-Ethernet) compliant and can not negotiate voltage levels like PoE. It will likely destroy any "ethernet" devices you connect (laptops, switches, IP cameras, etc).

We are not responsible for accidents or problems caused by your use or misuse of these modules.

Recycling program

If you outgrow the need for these modules, we will gladly accept returns in order to recycle, refurbish, and reuse the components for future use. In that case we will provide you with a lovely discount on future purchases from our store. Please note, we refuse to recycle modules which are severely damaged, non-functional, or soldered with lead based solder. They will be disposed of and no discount will be provided. Please use lead-free solder even if you don't plan to return the modules when they've reached their end-of-life.

For tracking and logistics, please contact us and wait for approval before making any returns. We may ask for photos of the modules before hand, and we may refuse to accept returns for any reason. Return shipping is paid by the sender and does not require a tracking number for low volumes. You can ship it by boat even if it takes months to reach Japan :) Thank you for understanding.

Privacy policy

We will not use customer information for any purposes other than shipping items, handling returns and defects, and customer support. We must provide customer contact information and shipping details to our mailing agent (Japan Post) through their online shipping website, which may be shared with third parties without our knowledge or consent. Please contact Japan Post to inquire about their privacy policy. We will not store customer contact information locally or on external cloud servers for more than 30 days after shipping the items (excluding information stored on Tindie which we may or may not be able to delete).