IBOX FMT2BT Car FM transmitter
Table of Contents
1. The device
This is a "cup-shaped" car FM transmitter that supports:
- bluetooth speakerphone
- MP3 playback from microsd
- MP3 playback from USB sticks
It's OEM'd by IBOX (https://www.ibox.pl/akcesoria-samochodowe/2050-fmt2.html) and available in many electronics stores in Poland.
2. The internals
The internals consist of only 1 PCB with all of the connectors and buttons. There is a vertically mounted 5 V power supply which has been unsoldered to make better view of the board. The board has "AD-BT-A23 V1.0" and "2016.11.21" silkscreened on it. The PCB photos with all of the important parts highlighted:
| Designation | Label | Description | Type | Datasheet | Notes |
|---|---|---|---|---|---|
| 1 | 5V/2.1A | External power output | USB-A connector | ||
| 2 | 7-segment 3.5 digit display | Transmit frequency | |||
| 3 | PLAY | USB stick for MP3 playback | USB-A connector | ||
| 4 | Micro-SD card slot | ||||
| 5 | LED9 | Status LED | |||
| 6 | FM trasnmitter | QN8027 | http://down.cosou.com/xintechsz.com/QN8027.pdf (mirror) | ||
| 7 | Bluetooth Antenna | Can transmit RDS | |||
| 8 | U1 | Main SoC | JL AC1749DEP587-01 | LQFP-48, ZhuHai JieLi (珠海杰理) | |
| 9 | Power supply input (unsoldered) | ||||
| 10 | C22 | RF coupling capacitor | |||
| 11 | Microphone connector |
I was unable to find any information about the particular SoC when searching for the exact mark on it. This is likely because JieLi makes a number of chip "families" marketed towards different products and then makes a unique label on each chip based on the exact customer/product it's supposed to go.
By looking at their site I figured that for my device the closest one should be the Jerry Bluetooth series chip AC690N/AC692N.
I found some AC6921A chips on aliexpress http://aliexpress.com/i/4001141547298.html which had the same case and a pinout diagram in the auction:
As well as AC6901 chips http://aliexpress.com/i/10000054405573.html with similar pinout diagrams:
I tried to match both of these chips to what I was seeing on the board but unfortunately none of them match. The pinout that I was able to verify so far:
Some other links discovered during research:
https://github.com/christian-kramer/JieLi-AC690X-Familiarization
This is information about the AC690X Bluetooth chip from the same company. This one is different (different package) but things like flashing protocol and so on can be similar.
JL Bluetooth development board chip AC692N series 6925A/6926A/6925B dual mode 5.0 Audio BLE
A development board for the 692X series chips. The development board description provides a convenient link to download an SDK and documentation for the development board: https://drive.google.com/drive/folders/1_rg1CTtwDWYpuCx29A9cRrXnMHIq35l0 (mirror)
JL Development Board Support JL 690X Whole System Jieli Bluetooth Development Board
A development board for the 690X chip, this one unfortunately doesn't come with a SDK download link.