RS485 Breakout with 48V Passthrough Building Block Board — Part 4

RS485 Breakout with 48 V Passthrough Building Block Board — Part 4#

The first run of the RS485 breakout boards arrived today.

It is always a bit of a buzz to see something move from a design on a screen into a physical item: manufactured, assembled, and ready to be tested.

This board is part of my wider set of building block boards. The idea is to create small, reusable hardware modules that can be used in prototypes and small embedded systems without having to redesign the same supporting circuits every time.

In this case, the board provides an RS485 interface with a 48 V passthrough section. The intention is to make it easier to experiment with distributed nodes where communication and power may need to run through the same cable route or enclosure wiring.

First Impressions#

The first thing I noticed was a text error on the silkscreen — naturally.

That is slightly annoying, but also not especially surprising. Sometimes you can stare at a design for hours on a screen and still miss something obvious. Then, as soon as it appears in a different medium, the mistake jumps out immediately.

It is very similar to writing a document and not noticing a spelling or punctuation error until you print it out and read it back on paper.

The silkscreen issue will be fixed in the next revision of the board. For now, if that is the only thing wrong with this first run, I will be more than happy.

Initial Bring-Up Checks#

After the first visual inspection, I started with a cursory check of one of the manufactured boards.

At this stage, I am not trying to prove that every part of the design is perfect. The goal is simply to make sure there are no immediate show-stopping issues before applying power and moving on to more functional testing.

The initial checks included:

• visually inspecting the board;
• checking continuity on the main tracks;
• checking for obvious shorts;
• confirming the 3.3 V input polarity protection behaves as expected;
• powering the board correctly;
• checking for the usual sign of life from the indicator LED.

So far, the 3.3 V side of the board behaves as expected. The polarity protection works, and when powered correctly, the LED comes on.

That is a small step, but an important one. It means the board has at least passed the first basic sanity check.

Waiting on the 48 V Supply#

The one thing I could not test today was the 48 V side of the board.

I do not currently have a suitable 48 V power supply on hand, but one should be arriving in the next couple of days. Once that arrives, I will be able to wire it in and start checking the passthrough section properly.

That testing will need to be done carefully. The board is not just a logic-level RS485 breakout; it also carries a higher-voltage supply path, so I want to verify that side of the design separately before treating it as usable.

The next set of checks will likely include:

• applying 48 V with current limiting where possible;
• confirming correct polarity and voltage at the relevant terminals;
• checking the passthrough output;
• checking protection behaviour;
• confirming there is no unwanted interaction between the 48 V section and the logic side of the board.

Next Step: Communication Testing#

Once the basic electrical checks are complete, the next priority is to plug two boards into a microcontroller setup and try to send some basic messages over a length of cable.

That will be the real functional test for the RS485 side of the design.

The first test does not need to be complicated. A simple transmit-and-receive test between two nodes will be enough to prove that the transceiver circuit, termination strategy, connector layout, and control signals are all broadly behaving as expected.

After that, I can start looking at longer cable runs, noisier environments, and eventually the kind of practical setup this board was designed for.

Closing Thoughts#

This is still an early version of the board, and there is testing and validation still to do.

The silkscreen mistake is irritating, but not serious. The important thing is that the first physical boards are here, the initial power checks look promising, and the design has moved from theory into something I can actually test on the bench.

That is always one of the most satisfying stages of a hardware project.

The next job is to validate the 48 V side and then get two boards talking to each other over RS485.

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