HiLetgo 2pcs CC2540 CC2541 AT-09 Serial Wireless Module BLE 4.0 Bluetooth Module Compatible HM-10The information below was determined experimentally by trial and error, so might be incomplete or inaccurate. If you find any discrepancies or have additional information, please post for others to see. (A datasheet would have been nice.)The default name, PIN, and baud rate is BT05, 123456, and 9600 respectively.The AT+HELP command will display more commands than the module actually uses.Commands are entered with no extra spaces, characters, or symbols, and should be sent with "Both NL & CR" on an Arduino terminal or equivalent.Entering commands without any parameters will cause the device to display the current status. (Except for AT+SLEEP which toggles sleep.)Certain commands will cause the next command to be ignored, so it's good to follow every command with a simple "AT" command.There are probably eight baud rates, but only six of them work properly, and two of them will possibly permanently incapacitate the device.BAUD8 = 115200BAUD7 = 57600BAUD6 = 38400BAUD5 = 19200BAUD4 = 9600BAUD3 = 4800BAUD2 = 2400, but communication with the terminal is ALMOST non-existent. (Only the "AT" command works. The 2400 rate was confirmed with an oscilloscope.)BAUD1 = 1200 ???The following commands do not work (they return an error) even though they are displayed:AT+ADDR Get local bluetooth address.AT+RENEW Restore factory default.AT+STATE Get current state.AT+PWRM Get/Set power on mode(low power).AT+PARI Get/Set UART parity bit.AT+STOP Get/Set UART stop bit.AT+SHOW Show the searched slave model.AT+IMME System wait for command when power on.AT+START System start working.These commands only work in Master mode:AT+INQ Search slave model.AT+CONN Connect the index slave model.These are the remaining commands:AT Check if the command terminal work normally.AT+RESET Software reboot.AT+VERSION Get firmware, bluetooth, HCI and LMP version.AT+HELP List all the commands.AT+NAME Get/Set local device name.AT+PIN Get/Set pin code for pairing.AT+BAUD Get/Set baud rate.AT+LADDR Get local bluetooth address.AT+DEFAULT Restore factory default.AT+POWE Get/Set RF transmit power.AT+SLEEP Sleep mode.AT+ROLE Get/Set current role.AT+UUID Get/Set system SERVER_UUID.AT+CHAR Get/Set system CHAR_UUID.Example Master mode only commands and responses:AT+INQExample response:+INQS (Starting inquiry.)Scanning...+INQ:1 0x7BD847B7C30A+INQ:2 0x463CB2D55634+INQ:3 0x60B86EF2FDD9+INQE (Ending inquiry.)AT+CONN2 (AT+CONN1, AT+CONN2, etc depending on which device is to be connected.)Example response:+CONN:2 (If not connected.)or+CONN:2Connected (If connected.)Other examples of commands and responses:ATExample response:OKAT+RESETExample response:OKAT+VERSIONExample response:+VERSION=v6.1AT+NAMExxxxxxxxxxxxxxxxx (Almost any symbol, number, or character, including spaces, 1 to 16 positions long)Example response:+NAME=xxxxxxxxxxxxxxxxxAT+PINxxxxxx (Almost any symbol, number, or character, including spaces, exactly 6 positions long)Example response:+PIN=xxxxxxAT+BAUD7Example response (uses original baud to send message):+BAUD=7OKAT+LADDRExample response:+LADD=3881D719C147AT+DEFAULT (+NAME=BT05, +PIN=123456, +BAUD=4, +POWE=3, +SLEEP:OFF, +ROLE=0)Example response:OKAT+POWE1 (POWE0, POWE1, POWE2, POWE3 - min RF power to max RF power, respectively. ~ 25 dB total range.)Example response:+POWE=1AT+SLEEP (Sleep mode toggles ON/OFF, but it always draws ~ 9 mA, regardless of connection status, so I don't see the purpose.)Example response:+SLEEP:ONAT+ROLE1 (ROLE0 is slave mode and ROLE1 is master. No other modes.)Example response:+ROLE=1AT+UUIDExample response:+UUID=FFE0AT+CHARExample response:+CHAR=FFE1

Just like other reviews say, these are a different model than almost any guides you can find online, I never found any guides that used this exact model. I had to cobble together the use from multiple sources. Its default BAUD rate is 9600, which it tells you is "BAUD4". It can't go up to 115200 so I don't believe it can upload sketches via bluetooth. I needed a special app to connect to this, I couldn't connect from my bluetooth widget on my Mac.However I got the TXRX connection to work without the resistors being wired into the lines, in fact those resistors messed up the communication. And actually communicating to this module was easier than a lot of guides I found online set me up for. Because my computer needed a special Bluetooth app and I can't upload sketches wirelessly I returned it. But if I needed bluetooth communication between my comp/phone to my Arduino this would be a good one, it would be better if it had real documentation online for this SPECIFIC model.

Working on the software to initlize the communication chips.I am now able to connect and list characteristic registers. Appears to be good product.

It took me a while to make it run. This is not an original HM-10 but it does work out of the box.IT IS a BLE device. So it won't pair like an old Bluethooth 2.0. You need a special APP or your own APP to be able to pair with it. No password or anything like that needed.If you have not written your own app yet, standard "DSD TECH Bluetooth" for iOS and Android works fine to test.

**Update 4/26/2021**Fixed it David S. So in your IDE serial console, Make sure you have Newline & Carriage Return both selected in the bottom-rightStill undecided how this works - trying to figure out but as David S says there's little to no documentation. By the way David, you saved my hide; I was about to get mad when I realized what was happening.It is some weird carriage return/ASCII encoding error.The device is tricky to figure out but slowly. David you're kinda right. Just use a space afterwards/any character and the AT commands work just fine.