SimHub breaks my button box or custom wheel
Last updated · SimHub 9.11.22
SimHub finds Arduinos by scanning serial ports, and that scan opens and probes every port it is allowed to — including one belonging to a button box, a custom wheel or another piece of hardware that did not expect to be interrogated. The result is a device that misbehaves or stops responding whenever SimHub is running, which reads as an incompatibility and is really a scan. The fix is to control what gets scanned in SimHub's Arduino scan settings so those ports are left alone. If you do not use any Arduino features at all, the cleaner answer is to turn Arduino support off entirely with the "Arduino Disabled" button, which stops the scan happening in the first place.
The tell for this one is timing: the other device is fine until SimHub starts, and fine again when it closes. Nothing in the other device's own software will explain that, because the cause is not in it.
Why a scan breaks things
There is no directory of serial devices that says what each one is. Discovering an Arduino means opening a port, sending something, and seeing whether a SimHub sketch answers. That is the only way it can work.
Most devices ignore being opened and probed. Some do not. A microcontroller-based button box or custom wheel may reset when its port is opened — that is standard behaviour on many boards, not a fault — or may misread the probe as input and end up in a state it does not recover from.
The diagnostic. Close SimHub completely and use the other device for a while. If it behaves, and misbehaves again the moment SimHub launches, this is your problem and no amount of reinstalling the other device's drivers will touch it.
The two fixes
Limit what SimHub scans
In SimHub's Arduino settings there is control over the serial port scan engine. Exclude the ports your other hardware uses, so SimHub never opens them. This is the right answer if you do use Arduino features and just need the two to coexist.
Or turn Arduino support off entirely
If you have no Arduino at all — you are here for dashboards, ShakeIt or overlays — click the Arduino Disabled button. No scan runs, so nothing gets probed, and you lose nothing you were using.
Find the port first. In Device Manager, expand Ports (COM & LPT), then unplug the button box and plug it back in while watching the list. Whatever disappears and returns is the port to exclude.
COM numbers move. Windows assigns COM numbers per device and per port, so plugging the same button box into a different USB socket can give it a different number — and an exclusion written against the old one no longer protects it. If the problem returns after you have rearranged cables, check the number before assuming the setting failed.
What this is not
Two other SimHub problems look adjacent and have different causes:
- UDP conflicts — two applications wanting the same telemetry socket, typically SimHub and CrewChief. That is network, not serial, and has its own page.
- Arduino not detected — the opposite complaint. There the scan is not finding something it should, and the usual cause is a charge-only USB cable.
It is worth being sure which you have, because the fix for this page — scanning less — makes the detection problem worse.
Common questions
Why does my button box stop working when SimHub is open?
SimHub scans serial ports looking for Arduinos, and opening the port your button box is on can reset it or leave it in a bad state. Exclude that port in SimHub's Arduino scan settings, or disable Arduino support entirely if you do not use it.
How do I stop SimHub scanning a particular port?
Through the serial port scan settings in SimHub's Arduino configuration, which is what the scan engine reads. Find the port number first in Device Manager under Ports (COM & LPT) by unplugging the device and watching which entry disappears.
I do not own an Arduino. Can I turn all this off?
Yes, and you should — there is an "Arduino Disabled" button. With Arduino support off no scan runs at all, so nothing on any serial port gets probed, and you lose nothing you were using.
Is this the same as the CrewChief UDP conflict?
No. That one is two programs competing for the same telemetry network socket. This is SimHub opening a serial port that belongs to a physical device. Different layer, different fix.
The fix worked and then stopped working.
Check the COM number. Windows can assign a different one when a device is moved to another USB socket, and an exclusion written against the old number no longer covers it.
Could this damage my hardware?
No. A serial probe is data, not voltage. The worst case is a device that resets or gets confused until it is power-cycled.
Sources
Related guides
SimHub is developed independently by Wotever and is not affiliated with OESimRacing. This page was checked against SimHub 9.11.22 on 4 August 2026; where the interface has moved on since, the version stamp tells you how far. More on what SimHub is and what it costs.