CH9141 BLE Chip and IOS BLE Terminal App

CH9141 BLE Chip

April 2026 (c) RLamb

The $4 bluetooth chip/modules trivialize making your UART wireless. Essentially just connect TX and RX pins to your hardware UART and go. Ive even just put the raw chip (+ 32mc xtal no caps needed) right onto many of my dev PCBs.

Howto:

Get 2 ch9141 (modules or chips and 32mc xtals)
Connect ch9141 GND, VCC, TX, RX to generic usb-serial-adapter GND, 3.3V, RX, TX pins, respectively. Usb adapter will be communicating with ch9141 at 115200 baud, say at /dev/ttyUSB3
Compile ch9141.c. ("cc ch9141.c -o ch9141")
./ch9141 /dev/ttyUSB3
This will enable AT commands with "AT..." That is actually 3 dots after AT (FWIW, "AT+EXIT" at the end disables AT command mode and puts the chip back in transparent passthrough). The program then queries the ch9141 for a bunch of stuff. See here for a full description of the AT commands and chip capabilities. The result for "AT+MAC?" is important. Write the mac address down as this will be used to make a connection.

Set the chip to DEVICE mode by doing

./ch9141 /dev/ttyUSB3 "..."
./ch9141 /dev/ttyUSB3 "+BLEMODE=2"
./ch9141 /dev/ttyUSB3 "+EXIT"

start your favorite terminal app listening on this port, eg,
```
screen /dev/ttyUSB3 115200
```
Now connect up a second ch9141 module to a usb-serial-adapter like above and do ./ch9141 /dev/ttyUSB4 for that one to test.

Set this chip to HOST mode by doing

./ch9141 /dev/ttyUSB4 "..."
./ch9141 /dev/ttyUSB4 "+BLEMODE=1"
./ch9141 /dev/ttyUSB4 "+EXIT"

connect to the other chip with:

./ch9141 /dev/ttyUSB4 "..."
./ch9141 /dev/ttyUSB4 "+CONN=03:E9:79:E5:66:E4"
./ch9141 /dev/ttyUSB4 "+EXIT"

where 03:E9:79:E5:66:E4 is the mac address you wrote above.

start your favorite terminal app on this port, eg,
```
screen /dev/ttyUSB4 115200
```
Try typing chars on either terminal screen. You should see the chars on either screen.

You have established a two way serial connection. Read the manual for other functions such as saving configurations.

But, wouldnt it be nice if I could use a console app for the host side instead of a second ch9141 and serial to usb adapter, i.e., a BLE terminal app. Looked around the net and there seemed to be many of these but none that would just give me a terminal screen after connecting to the particular ch9141 protocol. I probably just missed something, but it would also be nice to have the source/build environment for the app so that I could adapt to my own particular products (eg, like adding additional encryption and custom UIs). So decided to re-embark down that dreaded road of ios/android/non-C app/UI development. But wait, I keep reading about this AI thing...

Claude IOS BLE Terminal app for CH9141

Sheesh!

$ claude -p "please write an ios ble terminal app."

Uh...WTF...after about 10min Claude just dumped on my terminal screen 6 source code files and short setup instructions to build the app here! Didnt ask me any questions. Seemed to know exactly what I was looking for. Sure there were a few hurdles* to compile and get it onto my ipad/iphone but wow! This would have taken me - an un-experienced app/swift/apple hating old school C programmer - a long time (Ive done it before for NFC).

F.U.D was followed by - hmm.. I hate writing this sort of user facing code. Its tedious and boring (unlike writing embedded systems, net protocols, device drivers). So this AI-thing may be a godsend for folk like me though a problem for some. The true implications will take months and many beers for me to comprehend.

*yeah, spent a day just trying to update my apple xcode, certificates, etc. Ended up bricking an old mac mini and then had to buy a throw away macbook neo; and then relearning counter intuitive (for me) apple device usage. Then just a few simple SWIFT coding errors by claude. But then worked!