JDY-31 Bluetooth Module Review and Testing

I bought a couple cheap Bluetooth modules from AliExpress. My idea is to use them to convert serial interfaces to Bluetooth and allow wireless operation of the devices. I wrote this instructable to share my experience on setting up and using these modules.

JDTY-31 Bluethooth Module -> https://pt.aliexpress.com/item/32998624269.html

A USB serial converter -> https://pt.aliexpress.com/item/32757421855.html

3 x 10k 1/4W resistors (from my pieces box), a breadboard and some jumper wires

The USB serial converter is an USB plug with 4 wires. On the one I have they are the following

• black - ground
• red - 5V power supply
• white - Rx
• green - Tx

The module can be powered from 3.6 up to 6V so the USB converter can be used as a power supply. The Tx and Rx signals are a bit more tricky as the USB converter signals are 5V and the module's signals are 3.3V. From the module to the converter there is no problem because the levels high and low are correctly recognized. But from the converter to the module the 5V output must be converted to 3.3V. The 3 10k resistors in series with the Tx of the converter make a voltage divider for that.

See the picture. The 4 jumper wires connect to the USB converter. Do not forget to cross the Tx and Rx connections. This means that the white jumper connect to the green converter wire and the green jumper connects to the white converter wire.

The JDY-31 requires the commands to be sent with a <CR><LF> termination and with no pauses. Most terminal emulators fail to do that either sending characters as they are typed or failing to send the correct <CR><LF> sequence.

After much fiddling I found that termite works best. Download just the program from the developer's page at https://www.compuphase.com/software_termite.htm and unzip to your favorite location. In the settings change to the USB converter's port and choose the Append CR-LF option.

The command set of the JDY-31 is very short and it does not respond to the most common AT and AT+HELP commands.

AT+VERSION
+VERSION=JDY-31-V1.35,Bluetooth V3.0

For my purpose I do not want the module sending log messages to the controlled device so I used the following

AT+ENLOG0
+OK

As expected there is no manual on these cheap products from china... even when they seem to have a link to some sort of documentation it just is not valid anymore. I have attached the manual I found on the internet before buying.

The module is very basic, I have not found a way to change bits, parity, stop, etc but the devices I want to connect to are also very basic and do work with the default. Configuration is very simple, just needs an USB to serial converter.

In my opinion for less than 2$ it is very good if more fancy configurations are not needed.