2 layers24 × 27.9 mm
2 layers24 × 27.9 mm
Rs232IsoFEC
medo64/Rs232IsoFEC2Framework laptop expansion card exposing isolated RS-232 interface
- Size
- 24 × 27.9 mm
- Copper layers
- 2
- Thickness
- 0.8 mm
- Parts
- 25
- Nets
- 26
- Pads
- 121
- Tracks, vias
- 248, 29
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 2 Nov 2023
- Updated
- 29 Sep 2025
Overview
Rs232IsoFEC is an open-source printed circuit board by medo64, from the medo64/Rs232IsoFEC repository on GitHub, published under the MIT licence. It is a 2-layer board of 24 × 27.9 mm with 25 parts on 26 nets, routed with 248 tracks and 29 vias.
It is built around the ADM3251EARW, FT232RL and B5B-XH-AM, with the PESD12VL2BT among its other parts. Its parts include 11 capacitors, 5 resistors, 2 ICs, 2 connectors and 1 diode.
Main components
4
ADM3251EARW
SOIC20Isolated, Single-Channel RS-232 Line Driver/ReceiverAnalog DevicesUncategorised
FT232RL
SSOP-28-208mil-40℃~+85℃ 3.3V~5.25V、4V~5.25V USB 2.0 USB to UART SSOP-28-208mil USB Converters ROHSFTDIUSB Converters
B5B-XH-AM
插件,P=2.5mm-25℃~+85℃ 1 14.9mm 1x5P 2.5mm 250V 3A 5 5.75mm 5P 7mm Brass K Pin、With post PA66 Through Hole Tin UL94V-0 White XH 插件,P=2.5mm Wire To Board Connector ROHSJSTWire To Board Connector
PESD12VL2BT
SOT-23-55℃~+125℃ 10V 12V 17.5V 50nA 80W@8/20us 8A@8/20us 8pF、15pF ESD IEC 61000-4-2、IEC 61000-4-5、IEC 61000-4-4 SOT-23 ESD and Surge Protection (TVS/ESD) ROHSTECH PUBLICESD And Surge Protection (TVS/ESD)
README
README.mdIsolated RS-232 Framework Expansion Card
This Framework laptop expansion card will show up on your system as a serial device and allow for isolated RS-232 communication up to 460,800 baud rate.
UART Pinout
To connect to this board, one has to use a 5-pin JST XH connector. The following table represents the pinout, pin 1 being on the left as looking into the expansion card. Note that pins 1 and 5 are not internally connected.
| # | Ref | Description | DB9 |
|---|---|---|---|
| 1 | - | Not connected | 8 |
| 2 | RXD | Receive data | 2 |
| 3 | GND | Ground connection | 5 |
| 4 | TXD | Transmit data | 3 |
| 5 | - | Not connected | 7 |
As power consumption is low, wires can be almost any AWG. I would recommend using 24 AWG wire 0.25 mm² as they allow for greater compatibility with other connectors.
Supported Speeds
This board employs the FT232R as its UART chip, and consequently, it supports all the baud rates this chip can handle up to 460,800 baud which is the limit of isolator chip used. The table below lists the standard baud rates.
| Baud rate | Actual | Error | Divisor |
|---|---|---|---|
| 300 | 300 | 0.00% | 10000.000 |
| 600 | 600 | 0.00% | 5000.000 |
| 1,200 | 1,200 | 0.00% | 2500.000 |
| 1,800 | 1,800 | 0.00% | 1666.625 |
| 2,400 | 2,400 | 0.00% | 1250.000 |
| 4,800 | 4,800 | 0.00% | 625.000 |
| 7,200 | 7,201 | 0.01% | 416.625 |
| 9,600 | 9,600 | 0.00% | 312.500 |
| 14,400 | 14,406 | 0.04% | 208.250 |
| 19,200 | 19,200 | 0.00% | 156.250 |
| 28,800 | 28,812 | 0.04% | 104.125 |
| 38,400 | 38,400 | 0.00% | 78.125 |
| 57,600 | 57,692 | 0.16% | 52.000 |
| 115,200 | 115,385 | 0.16% | 26.000 |
| 230,400 | 230,769 | 0.16% | 13.000 |
| 460,800 | 461,538 | 0.16% | 6.500 |
While rates above this can be set, they are not guaranteed to work.
You can check my blog and other projects at www.medo64.com.
Parts
25| Qty | Value | Footprint | References |
|---|---|---|---|
| 9 | 100n | Medo64:C (0805) | C2, C3, C4, C5, C6, C7, C8, C9, C10 |
| 3 | 1K | Medo64:R (0805) | R1, R2, R3 |
| 1 | 105444-0001 | Medo64:P USB C 3.2 Edge (24w) | P1 |
| 1 | 10K | Medo64:R (0805) | R5 |
| 1 | 10n | Medo64:C (0805) | C1 |
| 1 | 4u7 | Medo64:C (0805) | C11 |
| 1 | 5K1 | Medo64:R (0805) | R4 |
| 1 | 600R | Medo64:L (0805) | L1 |
| 1 | ADM3251E | Medo64:U Transciever RS232 Isolated ADM3251E (SOIC-20) | U2 |
| 1 | B5B-XH-A | Medo64:J JST XH Edge [UART] (5w) | J1 |
| 1 | DMP3099L-13 | Medo64:Q MOSFET-P (SOT23-3) | Q1 |
| 1 | FT232RL | Medo64:U Transciever UART FT232RL (SSOP-28) | U1 |
| 1 | PESD12VL2BT | Medo64:D TVS SM05T1G (SOT23-3) | D1 |
| 1 | RX | Medo64:DS (0805) | DS1 |
| 1 | TX | Medo64:DS (0805) | DS2 |
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Questions
How big is the Rs232IsoFEC PCB?
It measures 24 × 27.9 mm and has 2 copper layers, 0.8 mm thick.
What parts does the Rs232IsoFEC use?
25 parts, built around the ADM3251EARW, FT232RL, B5B-XH-AM and PESD12VL2BT. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Rs232IsoFEC KiCad files?
From the medo64/Rs232IsoFEC repository on GitHub, at the commit this page was made from: the board is src/Rs232IsoFEC.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Can I use the Rs232IsoFEC design in my own project?
Its repository publishes it under the MIT licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).