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Bluetooth interface for STAG 4 or QBOX gas installation

weryfany  37 28764 Cool? (+14)
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TL;DR

  • Built a compact Bluetooth interface for STAG 4 or QBOX gas installations, combining a STAG plug, an HC-05 Bluetooth module, and a universal remote-control housing.
  • A reed switch and a nearby magnet reprogram the interface between STAG 4 and QBOX modes, with power from a 7805 stabilizer or a 4.9V step-down converter.
  • The original interface cost about PLN 80, and any laptop with Bluetooth replaced the old RS-232 cable setup.
  • It corrected settings and updated drivers in multiple vehicles, and the STAG QBOX controller can communicate with an Android phone app for parameter viewing.
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Hello everyone, I was inspired by another thread on the electrode related to the 232 interface for the gas installation.
I made the interface presented here over 2 years ago, in the meantime, about a week, new versions were created. The final version was quite universal. It can be reprogrammed to STAG 4 or QBOX by bringing the magnet closer.

I used the STAG plug, the HC-05 bluetooth module, the 7805 stabilizer (or the step-down converter set to 4.9V), the reed switch which has contacts for reprogramming the settings, universal remote control housing, hot glue, heat shrink tubing.
Thanks to this interface, I corrected settings and updated drivers in my and other vehicles.

I wanted it to be small, handy, durable and that's what it is.

Photo of the first version:





And the final one after all modifications:



And the end result:



The original one at the moment is about PLN 80
but over 2 years ago it was not so colorful.

Any laptop with bluetooth was enough to work, and the 232 port and cable tethering were a thing of the past.

Each intervention in the controller is recorded / saved in it (in the controller).
The installer, if he hooks up and programmed on the same computer, will pop up a message that he was programmed with a different computer.
It was not like that in my case.

In the STAG QBOX controller it communicates with the Android phone application (parameter preview)

HC-05 settings:



AT commands:

Code: ARM assembler
Log in, to see the code
About Author
weryfany
weryfany wrote 1020 posts with rating 146 , helped 59 times. Live in city Zamość. Been with us since 2007 year.

Comments

Sebek6543210 30 Jan 2019 06:41

"interference" - that is, the readings are recorded, doesn't it count? Was there a lot of combining with the HC-05 configuration? [Read more]

byrrt 30 Jan 2019 08:42

How is communication with these two drivers different? What is this reed switch for? [Read more]

weryfany 30 Jan 2019 08:49

Just connecting to the driver, if I remember correctly (over 2 years ago it was) A banal configuration, a USB programming cable that saves disks from TX, RX and GND. I will add 3 more photos because... [Read more]

jawa1993 30 Jan 2019 11:57

Each connection to the controller is saved. I don't remember which and which company the new drivers have a connection counter, after which they are "full", they are blocked and need to be replaced... [Read more]

weryfany 30 Jan 2019 13:40

If there are such drivers, a colleague could mention their names, what companies / models they are, because STAG does not protect its devices in this way, and that's why I always choose STAG, because... [Read more]

Sebek6543210 30 Jan 2019 20:59

Were there attempts to connect with other drivers, e.g. Lovato? [Read more]

weryfany 30 Jan 2019 21:03

Not only STAG 4 and after reprogramming STAG QBOX I tried with Zenit, despite supplying external power after the first attempt, I gave up due to lack of time. [Read more]

noel200 01 Feb 2019 08:47

So the hc-05 module fits right out of the box? I do not need to change anything? You only entered the password and name, but it is not essential for the connection between the module and the stag, and... [Read more]

zbyz 01 Feb 2019 18:22

Hello. I will present you my battles with a similar topic. A year ago, I glued something similar to the STAG-300 ISA2, but due to my inattention, I released my HC and probably the communication inputs... [Read more]

weryfany 01 Feb 2019 19:09

I programmed the HC-05 as above 3 print screens - 9600 for stag 4 (I had the eco version) Well, it makes no sense to pour the whole glue. I will tell you that the versions with the 7805 stabilizer, despite... [Read more]

MACIEK_M 08 Feb 2019 19:45

Hello, great idea, I have the elements in a drawer, I will try to replace the wired interface with this one, we will see how it works. I didn't think it was that simple. :D [Read more]

MACIEK_M 11 Feb 2019 18:19

Werfany wrote: And you could enter the parameters for connecting to QBOX, I have GO-FAST, and the interface for STAG 4 ECO does not connect to it. [Read more]

weryfany 11 Feb 2019 19:51

At 100%, the speed of communication is higher, but I do not remember how much than in stag 4 [Read more]

MACIEK_M 11 Feb 2019 19:56

Can the communication speed be "previewed" on the wired internet connection to GO-FAST, because I have one, and I wanted BT? Are they unrelated? [Read more]

weryfany 12 Feb 2019 20:32

I have no idea what it's like with a wired one, I've never had one [Read more]

Arek1984 17 Feb 2019 03:27

Here you can find everything about the interface. https://lpg-forum.pl/interkietas-bluetooth-diy-t23813-795.html [Read more]

MACIEK_M 17 Feb 2019 10:43

-> Arek1984 Very helpful link, everything is thanks. :D [Read more]

MACIEK_M 04 Apr 2019 20:26

Hello, it took a while, but it worked. My HC-05 module failed to reprogram with Arduino, I don't know why. :D I had to order from Ali .. TTL UART converter, by the way I ordered a small 5V pulse... [Read more]

weryfany 05 Apr 2019 18:09

I would stick to the casing because it looks delicate, but it is important that it works and there is POWER; D [Read more]

FAQ

TL;DR: DIY Bluetooth interfaces for STAG 4/QBOX cost ≈ PLN 20 instead of the PLN 80 OEM unit; "I updated the driver without any problems" [Elektroda, weryfany, post #19361578] Build uses an HC-05 at 9600 or 57600 baud and a 5 V regulator.

Why it matters: Saves money, removes dangling cables, and lets you tune LPG maps from a phone.

Quick Facts

• OEM Bluetooth dongle price: ~PLN 80 [Elektroda, weryfany, post #17741134] • DIY parts cost: approx. PLN 15–25 (HC-05, 7805/step-down, plug, case) [Elektroda, weryfany, post #17741134] • STAG 4 baud rate: 9600 8N1 [Elektroda, weryfany, post #17741134] • QBOX / GoFast baud rate: 57600 8N1 [Elektroda, MACIEK_M, post #17886237] • Recommended supply range: 7–16 V car rail → 5 V regulator (≤ 50 mA) [Elektroda, weryfany, post #17747760]

Which gas ECU models work with a re-programmed HC-05?

Confirmed: STAG 4, STAG QBOX, Go Fast and CCY BT Basic QBOX when set to the correct baud rate [Elektroda, weryfany, #17743387; #19360967]. Others like Zenit may need different commands and were not fully tested [Elektroda, weryfany, post #17743387]

What AT commands do I need for a STAG 4 interface?

  1. Enter AT mode (key pin high).
  2. Send AT+UART=9600,0,0
  3. Send AT+PSWD=1234
  4. Send AT+NAME=AC STAG This keeps the default 8N1 framing and preserves ECU compatibility [Elektroda, weryfany, post #17741134]

How do I switch the dongle between STAG 4 and QBOX?

Install a reed switch on the HC-05 KEY pin. Bringing a magnet closes the switch, letting you re-flash the baud setting to 57600 for QBOX, then remove the magnet to return to normal mode [Elektroda, weryfany, post #17741542]

Why does my connection drop after a few seconds?

Voltage sag or noise on the 5 V rail often causes resets. Replace 78L05 with a buck step-down rated ≥ 500 mA and add 100 µF filtering; users report stable links after the swap [Elektroda, MACIEK_M, post #18468145]

Do I need level shifting between ECU (5 V) and HC-05 (3.3 V)?

Yes. Use a simple 1 kΩ–2 kΩ divider on ECU TX → HC-05 RX, and connect HC-05 TX directly; it has 3.3 V-tolerant inputs. Over-voltage killed one user’s ISA2 RX/TX lines [Elektroda, zbyz, post #17747638]

Is opto-isolation required?

No. Bluetooth already provides galvanic isolation; extra optos add cost and latency. Keep good wiring and a regulator; "there is no point in doing optoisolation" [Elektroda, neo_84, post #18469846]

Can I safely flash ECU firmware over Bluetooth?

Yes, several users updated STAG drivers wirelessly without issues [Elektroda, weryfany, post #19361578] Ensure phone or laptop battery is ≥ 50 % to avoid dropouts; a failed flash can brick the ECU (edge case).

How many connections can the ECU log before locking?

Some non-STAG units count connections and lock when the counter is full, but STAG controllers do not implement this protection [Elektroda, jawa1993, #17741929; weryfany, #17742161].

What’s the current draw of the finished dongle?

HC-05 draws ~30 mA when connected and peaks at 50 mA during discovery [HC-05 datasheet]. A linear 7805 wastes ≈ 0.3 W at 14.4 V, hence the recommendation for a 90 % efficient buck converter [Elektroda, weryfany, post #17747760]

How do I check the required baud rate if I only have a wired cable?

Connect the OEM USB interface, open STAG Gas Synchro, and note the COM port speed shown in the status bar. Use the same rate when programming HC-05 via AT commands [Elektroda, MACIEK_M, post #17770975]

Quick 3-step build recap?

  1. Wire ECU TX/RX/GND to HC-05 through a voltage divider and 5 V regulator.
  2. Enter AT mode, set baud (9600 or 57600) and name/pin.
  3. Enclose in a small remote-key housing and pair with phone/laptop. Build time: under 30 minutes [Elektroda, thread synthesis].
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