OBDLINK_SX_FORSCAN_MODS.pdf

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Modifying an OBDLINK SX OBD-II USB Adapter for use with FORScan
JBirdZee 2019
A hardware modification to the OBDLINK SX From Scantool.net allows FORScan to automatically select
between HS and MS CAN.
This procedure documents the steps on an already completed unit, therefore interior images will look
different from a new adapter.
The summary is that we will add a DPDT relay to allow the OBDLINK-SX to select MS CAN or HS CAN
operation using the RTS Handshaking line of the serial port. A schematic of the modifications is provided
as someone will certainly have a cleaner way of performing this mod. (I’m not proud of the flux residue
and melted plastic on my adapter from this mod)
This procedure requires the following:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Soldering iron, solder, solder wick
Fine gauge wire strippers
Electrical tape or heat shrink
Small side angle wire cutters to cut pins on a 2.54mm header
Insulated fine gauge wire (Wire wrapping ~30Ga is ideal, multiple colors is helpful)
2N3904 Transistor
1k-ohm Resistor
1N4001 Diode
DPDT Relay with 12V Coil, small enough to fit inside of adapter housing. I used an Omron G6S-
2G because I had several left over from other projects.
10. Optional SPST Switch of your preference: After the modification the adapter will default to MS-
CAN when using generic OBD Scan tools. The switch forces HSCAN operation for use with GM,
etc.
Schematic Modifications:
Schematic Modifications with explanations:
The FT232 USB-Serial IC U7 PIN
3 Provides MS/HS CAN
Selection. When RTS is asserted
(LOW), MSCAN is selected.
When RTS is de-asserted (HIGH),
HSCAN is selected
SPST Switch bypasses the FORScan
mode and forces HS-CAN all the
time when it is closed.
The relay is shown with the
contacts in the normally open state
(No coil power)
1N4001 protects the 2N3904
transistor from switching
transients off of the relay coil
There is an 8-pin right angle
header connecting the Logic
board to the OBD-II Connector
Riser board. Pins 4 and 5 are
the CAN+ and CAN-
respectively. They need to be
cut out and the signals get
routed through the relay.
Some of the terms used here:
NO= Normally Open
C=Common
NC=Normally Closed
CAN+ = CAN-H or CAN HIGH
CAN- = CAN-L or CAN LOW
Step 1. Remove four Philips-head screws from enclosure and expose PCB with OBDII connector.
Step 2: An 8-pin right angle connector is used to interface the OBD-II adapter logic to the connector
riser. The center two pins are the HS-CAN connections and need to be cut and removed as shown
below.
These two center
pins are cut away to
sever the HS-CAN
connection pair

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