Two iFlags connected, only one works in SimHub
Last updated · SimHub 9.11.22
Both are running the same firmware, so they report the same device name — and that name is compiled into the USB signature, not just shown in the interface. Windows and SimHub both treat one signature as one product, so the second iFlag is not missing, it is being read as another copy of the first. The fix is to reflash one of them with a different device name. A single letter is enough: any difference makes a different signature, and both then appear and can be configured separately.
Written for two iFlags because that is where we hit it, but nothing here is specific to them — it is the same for two of any identical device flashed from the same firmware. The tell is that each one works perfectly on its own. Plug in either and it is found; plug in both and one disappears. That pattern rules out cables, ports and power, which is where this symptom otherwise sends you.
Why the second one vanishes
SimHub does not identify a board by which socket it is in. It identifies it by what the board says it is, and that identity is baked into the firmware when you build it. SimHub's own firmware builder is explicit about this: the device name is compiled inside the firmware and the USB signature, and cannot be changed afterwards without building new firmware.
The same manual states the rule that makes two identical panels collide: one PID/VID couple = one "product/model". A PID/VID pair is how USB says what a device is. Flash two boards from the same firmware and you have not made two products, you have made the same product twice.
So this is not a fault. Everything is behaving as designed. Two devices are answering the same question with the same answer, and the software is believing them.
It follows that the problem is not confined to SimHub. Windows has the same difficulty at the same moment, which is why Device Manager is a useful place to confirm what is happening before changing anything.
The fix: reflash one of them
Only one of the two needs to change. Leave the first as it is — anything already mapped against it keeps working — and give the second a new name.
Unplug one of the two
Work with a single device connected, so there is no question which board you are about to flash. This is the step people skip, and flashing the wrong one costs you the mapping you had already done.
Change the device name in the firmware builder
Open SimHub's firmware builder for the connected board and change the device name field. One character is enough — "iFlag" and "iFlag2" are different signatures, and so are "iFlag" and "iFlagB". There is no benefit to a longer name; the builder itself asks you to keep names short and warns against shouting in capitals.
Upload it to that board only
Build and upload as normal. The board reconnects under its new identity, and its serial port name changes with it, because the port name follows the USB signature.
Plug the other one back in
Both should now be listed, each configurable on its own. Assign your effects to whichever is which — the names you just set are how you will tell them apart from here on.
Pick the name before you flash. The name cannot be edited later; changing it means building and uploading firmware again. It is worth choosing something you will still recognise in six months — "left" and "right", or "dash" and "wheel", beat "1" and "2".
Confirming it before and after
Windows will show you the collision directly, which is worth seeing once so you trust the diagnosis:
- Open Device Manager and expand Ports (COM & LPT).
- With both devices connected and sharing a name, you will not see two distinctly named entries the way you would for two different products.
- After reflashing one, the two appear separately, under different names and different COM numbers.
A quick sanity check. If a device is found on its own but never alongside its twin, the identity is the thing to suspect. If it is not found on its own either, this is not your problem — start with detection instead.
What this is not
This symptom is easy to mistake for three other faults, and none of their fixes will help:
- A charge-only cable or a bad port — that stops a device being found at all, including on its own. See Arduino not detected.
- A serial port conflict — that is SimHub disturbing some other piece of hardware by probing it, not two devices colliding with each other. See Serial port conflicts.
- Not enough power — a hub that cannot feed two boards drops them intermittently rather than hiding one cleanly. See LED power.
The distinguishing question is always the same: does each device work on its own? If yes, and only the pair fails, the identity is the cause.
Common questions
Why does SimHub only detect one of my two identical devices?
Because they are not two devices as far as USB is concerned. The device name is compiled into the firmware and into the USB signature, so two boards flashed from the same firmware present the same identity, and one signature is read as one product. Reflash one with a different name and both appear.
How different do the names have to be?
One character. The signature either matches or it does not — there is no partial matching and no benefit to a longer name. "iFlag" and "iFlag2" is enough.
Do I have to reflash both of them?
No, only one. The other keeps its name, its identity and anything you have already mapped to it.
Can I rename a device without reflashing it?
No. SimHub's firmware builder states the name cannot be changed after the fact without creating new firmware, because it is compiled in rather than stored as a setting. Choose the name before you upload.
Does this affect three or more devices?
Yes, and in the same way. Every device needs a name nobody else is using, so a third one needs a third name.
Does this only happen with iFlags?
No. It is not about the product, it is about the firmware: any two devices flashed from the same firmware carry the same name and the same USB signature, so two identical Arduino panels, two button boxes or two of anything else collide in exactly the same way and are fixed the same way.
Sources
Related guides
- Arduino not detectedWhere to start when a device is not found on its own, rather than only when its twin is present.
- Serial port conflictsThe other collision: SimHub's scan disturbing hardware that was not expecting to be probed.
- USB disconnectsFor devices that appear and then drop out, which is a power and cable problem rather than an identity one.
- RGB matrix panelsBuilding and configuring the kind of panel people most often run two of.
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.