BT1035 HFP-AG connection to car handsfree system fails

anthonysg

Hardware: FSC-BT1035, Firmware V6.1.1 (20240521)

Use case: I need the BT1035 to act as a "phone" (HFP-AG) connecting to a car's handsfree system (HFP-HF). Audio is routed via 3.5mm analog (AT+AUXCFG=1). Before purchasing, Feasycom sales confirmed the BT1035 supports this configuration.

Configuration:
AT+PROFILE=17 (SPP + HFP-AG)
AT+COD=5A020C (Phone device class)
AT+SSP=1
AT+AUXCFG=1
AT+NAME=ASGDEV,0

What works: Connecting to a bluetooth headset (HFP-HF) succeeds. After scanning with AT+SCAN=1, I connect with AT+HFPCONN=<address>. Pairing completes, +HFPSTAT=3 (connected) is received, and call simulation with AT+HFPRING works correctly.

What fails: Connecting to a car handsfree system (BMW/MINI iDrive). Two scenarios tested:

Car searches for devices, BT1035 in pairing mode (AT+PAIR=1, +DEVSTAT=7) — car discovers "ASGDEV" but reports "connection not possible" when selected.
BT1035 scans and finds car, then AT+HFPCONN=<car_address> — goes to +HFPSTAT=2 (connecting) for ₁₀ seconds, then falls back to +HFPSTAT=1 (standby). No +PAIRED event, no +HFPSTAT=3.

Question: Is there additional configuration required for HFP-AG compatibility with automotive handsfree systems? Is there a newer firmware that addresses this? Any suggestions for troubleshooting? I was able to connect using a BT1058 module in an earlier prototype, but couldn't use analog audio, which is why I'm trying the BT1035 now.

Thank you.

FAE_Gavin

anthonysg The FSC-BT1035 module currently does not support "random PIN code" pairing. Some car head units or Bluetooth devices use randomly generated PIN codes during pairing, while our module only supports fixed PIN code pairing (e.g., default 0000). This issue is related to the underlying pairing mechanism, not to specific Bluetooth profiles (such as A2DP or HFP).

Temporary suggestions:

Please check if your car head unit's Bluetooth settings allow changing the pairing method to a fixed PIN code (e.g., set it to 0000). If possible, set the car head unit's PIN code to match the module’s default (0000) and try pairing again.

Next steps:
Our R&D team has logged this as an improvement item and will evaluate adding support for random PIN code pairing in a future release.

anthonysg

FAE_Gavin Thanks for the reply. I understand that the car is using SSP which displays a PIN to match on the pairing device, which is more or less the standard way that modern cars do pairing. I can't see a way to work around this and in any case that would make the device very dependent on the bluetooth settings in different cars. Do you have a timeline for adding this support?

FAE_Gavin

anthonysg
We have confirmed that a fix will require firmware updates and additional testing.

Current estimate: approximately 2 months before a solution is available in a new firmware release.

We will keep you updated on the progress. If you have any further questions, please feel free to reach out.

anthonysg

FAE_Gavin Thank you Gavin, that's very helpful. I can focus on other elements of the solution in the meantime. Please keep me updated with your expected release date, and let me know if I can provide any further information on the proposed use case that may be of help.