1Buy the kit or DIY
The PCB gerbers aren't available yet, as I am offering these boards/modules for sale (in kit format available soon). If you want to DIY the boards, please wait a bit until I release the gerbers on GitHub.
2Solder the components
Every component is through-hole, so it's difficult to mess up. The only issues I can see are:
- placing the microcontroller (MAX3088) incorrectly
- shorting pins during hand-soldering
Otherwise there's no real skill required.
The board and components are lead-free and RoHS compliant.
3Set the slide switches
The DIP slide switches are in the OFF position by default (down, facing toward the edge of the board).
This setting puts the MAX3088 in driver mode (it sends data) because the RE and DE pins are pulled up to 5V by default, but this setting also allows one to control the RE pin through an external MCU.
The settings are printed at the top of the DIP switch:
- 1-2 OFF = RE and DE are brought high, the MAX3088 will be in driver mode (it sends data)
- 1-2 ON = RE and DE are brought low, the MAX3088 will be in receiver mode (it receives data)
- 1 ON, 2 OFF = DE tied low, RE tied high, the MAX3088 goes into low-power mode and disables both send and receive
4Add a jumper
There is a 3-pin 2.54mm header near the 5V voltage regulator.
This allows connecting VIN to the RJ45. If a jumper is placed in the ON position, then current coming into VIN will flow out through the RJ45, and vice-versa.
Of course, this can be dangerous depending on the setup, so placing a jumper in the OFF position prevents high voltages from reaching the RJ45 by disconnecting the VIN to RJ45 connection. That makes it possible to independently power each board through VIN, while still allowing differential data to flow through the RJ45 cable (on the DATA pins 1-2).
Caution!: do NOT touch the jumper while power is flowing into the module (either through VIN or through the RJ45).
5Test the setup
You'll need two of these modules to test it.
I know some people will be like: "this thing is so generic, can't I just use whatever 3-pin voltage regulators, pin headers, and fuses?
The answer is oh yes! Now of course you'll need to make sure of a few things:
- the fuse is sized correctly for your load
- the voltage regulator pinouts are exactly the same as the ones provided above
- the bypass capacitors are well spec'd for the voltage regulator
- the pin headers can handle the current you plan to draw
If you want to use many boards on a bus, omit the 120 ohm resistor unless the board is a "terminating node" (i.e: it's the last board on the bus).
The VIN and 3.3V traces are 1mm, so they might not handle much more than 2A.
Finally, it might be possible to swap the MAX3088 with a different transceiver such as MAX3085 or some other 8-pin DIP RS-485 transceiver, but make sure you read the datasheets!