I am attempting to use HM10 as central to read data from a sensor. The HM10 has been flashed with the latest firmware V710 to use the self learn functionality.
Here is the list of messages I am sending and receiving from the HM10
First I configure the HM10 as central and turn on some notifications. Then I connect to the MAC address of the sensor. I use the AT+FINDSERVICES? command to get the list of services, then find all the characteristics in the range of that uuid. The characteristics I am interested in is 0021.
But here is when the problems start. If I try to read that characteristic I get OK+DATA-ER, which the datasheet the characteristic does not have a read property. Same thing with notify.
But from the AT+CHAR command we can see handle 0021 has both read and notify. I have also tired reading from 001E handle and I get the same error. I am able to read data like the device name from another handle so I am able to get some data off the sensor.
I am wondering if the OK+DATA-ER response can mean something else? Or if the characteristic handle isn't correct somehow. If that were the case how would I find the correct handle?
I have tried connecting to the sensor on my iphone using the LightBlue app and I am able to both read and subscribe to the notification. I have also tried cloning the sensor as a virtual device on LightBlue and I am able to read and subscribe from the HM10 to the phone. So the issue seem to be between the HM10 and the sensor specifically and not with either device individually.
I figured it out. Turned out to be a security issue. The sensor would allow connection but no data would be accessible unless the connection was encrypted.
The BLE sensor required pairing when it first connect to a phone and does not subsequently so I missed that fact when I was trying to connect to it via the HM-10.
I don't believe the HM-10 supports pairing connection. I tried setting AT+TYPE to other than 0 but it would no longer connect to the sensor. I would get OK+CO11A but it wouldn't finish connecting.
I switched to an ESP32 board and used
BLEDevice::setEncryptionLevel(ESP_BLE_SEC_ENCRYPT);
This allowed me to read and subscribe to the characteristic.