#baudrate

SAE J1939 250k/500k Baud Rate Converter – Bridge Between Different CAN Bus Speeds

Easily connect 250k and 500k SAE J1939 CAN bus networks. This baud-rate converter bridges legacy and modern systems for seamless data communication.

From Concept to Market: The SAE J1939 250 k / 500 k Baud Rate Converter

The SAE J1939 250 k / 500 k Baud Rate Converter from Copperhill Technologies bridges communication between mixed-speed J1939 networks. Designed for reliability and ease of use, it supports wide voltage input, selectable termination, and a compact form factor—ideal for diagnostics, fleet integration, and development applications.

SAE J1939 250k/500k Baud Rate Converter

The JCOM.J1939.BRC converts SAE J1939 standard baud rates 250k to 500k and vice versa. The converter provides one CAN Bus port at 250k baud and another at 500k baud. The converter operates at voltages between 7 VDC and 32 VDC, therefore well-suited for operation with diesel engines.

This type of sound will never leave my brain.

but I should take a nap.

SAE J1939 250k/500k Baudrate Converter with Arduino Due - Source Code Included

There are scenarios where automatic baud rate detection does not apply, e.g., attempts to connect a 250k supporting device into an existing 500k network or vice versa, assuming that the device does not support baud rate detection. For such cases, one will require a baud rate converter. This post describes the implementation of such a converter using our Arduino-Based ECU Development Board with Dual CAN Interface.

SAE J1939 250k/500k Baudrate Converter Using Arduino Due With Dual CAN Bus Port

The above image shows a setup with a baud rate converter, represented by the larger board to the right. The other two boards (i.e., our  SAE J1939 simulator boards) represent two J1939 ECUs, one operating at 250k and the other at 500k CAN Bus baud rate. The baud rate conversion works in both directions, thus allowing full data exchange between the two nodes.

Following a series of copy-paste hacks scraped from various websites and forums, I was left frustrated and confused. Everything seemed to be set up properly, from baud rate through Node.js buffer code through the wiring.. yet I was still receiving nonsense messages into my audio interface.

After several days and rewrites, I was on the verge of giving up.. which is when most excellent breakthroughs happen. Here are the steps I took to effectively communicate Midi messages over the UART serial on the Raspberry Pi. 

This is a revised workflow from my previous post regarding Raspberry Pi setup, but has an important addition that made all the difference.

First, I edited /boot/cmdline.txt on the Pi:

sudo nano /boot/cmdline.txt

replace contents with:

dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 bcm2708.uart_clock=3000000 elevator=deadline rootwait

This enables the AMA0 serial port on the Pi to be used by Node. The important change here vs. my previous attempt is initializing the uart_clock to 3000000. I honestly have no idea what this is for, but thanks to this guy and his writeup for giving me something to try!

Second, I added some lines to the end of /boot/config.txt :

sudo nano /boot/config.txt

Add lines to end: 

# change uart clock to 2441406 for midi 31250 baud rate init_uart_clock=2441406 init_uart_baud=38400

This slows down the Pi serial baud rate to approximately 31250 if a serialport is opened at 38400 baud rate (one of the standard baud rates supported). Note that only after initializing the UART clock, this was successful.

Third, I modified write access to the AMA0 port to allow Node.js to use it

chown pi /dev/ttyAMA0

chmod a+rw /dev/ttyAMA0

I chose the Raspberry Pi as my primary communication mechanism for a couple reasons. First, I am already familiar with the device having used it on a couple hack projects this year. 

Second, after attempting to use the Pi with an Arduino to relay web events over serial and output Midi messages from the Arduino, I discovered a translation issue with differing baud rates between the devices. At this point, I chose to pair down my attempts and use only the Raspberry Pi.

Setting up the Pi to send midi messages is a little involved, but not over complicated. I referenced an excellent post by Silicon Stuff to hack the serial baud rate close to 31250 (Midi spec).

First, I hooked the Midi cable up to the Pi. 

Pin 1 (5v) goes through a 220 ohm resistor to Pin 5 of the Midi cable.

Pin 5 (Ground) goes to the ground Pin 2 of the Midi cable.

Pin 7 (TX - serial transmit) goes to Pin 4 of the Midi cable.

Second, I edited /boot/cmdline.txt on the Pi:

sudo nano /boot/cmdline.txt

replace contents with:

dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait

This enables the AMA0 serial port on the Pi to be used by Node.

Third, I added some lines to the end of /boot/config.txt :

sudo nano /boot/config.txt

Add lines to end: 

# change uart clock to 2441406 for midi 31250 baud rate init_uart_clock=2441406 init_uart_baud=38400

This slows down the Pi serial baud rate to approximately 31250 if a serialport is opened at 38400 baud rate (one of the standard baud rates supported).

Fourth, I modified write access to the AMA0 port to allow Node.js to use it

chown pi /dev/ttyAMA0

chmod a+rw /dev/ttyAMA0