Electrical – HM10 bluetooth module to discoverable state after connection break

bluetooth low energy

I am trying to setup a HM10 (or similar Bluetooth LE to serial module) but am having problems with it.

The problem is when I am connected to the device with my phone, it works great. Now, if I force close the app while connected (or walk out of range), the HM10 module never returns to a discoverable state until it is power cycled. I could not find anything in the documentation regarding this. I am not able to connect to the HM10 manually via its MAC address either.

The only fix I can come up with is to have my app send a heartbeat signal to the MCU (ATMega 328p) and if the heartbeat is not seen within its allotted time, it should send AT+RESET to the HM10.

There has to be a better way, but I am not able to find it. Please let me know what you think.

Thank you in advance.

http://fab.cba.mit.edu/classes/863.15/doc/tutorials/programming/bluetooth/bluetooth40_en.pdf

(This happens when using any generic BLE terminal app or a custom made app)
(Android and IOS)

Best Answer

I've worked on a project that involved an HM10 and experienced similar issues. Here are some ideas for debugging the issue:

Check the System LED function (PIO1) pin with a multimeter to determine if the HM10 is in a connected or disconnected state (see datasheet).

If it is in a connected state, that would explain why it is not emitting BLE advertisements. But if you physically remove it from any other BLE devices it can pair with and it remains in a connected status... this is strange.

What you may want to do next is check whether sending a reset signal to the HM10 will fix the issue. From what I understand, having the 328p sent AT+RESET may not work, as the docs state the way to sent AT commands to the device while it is in a connected state is from the remote device, and when the HM10 is in the remote control system work mode (AT+MODE2).

You can try sending a reset signal through the System KEY function (PIO0) by connecting it to ground for > 1sec. You can also try this for the RESETB (11) pin - I've found this one to be more reliable than PIO0. If this works, then you would just need to connect this pin to an output pin on the 328p and send a LOW signal to the HM10.

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Electronic – Bluetooth modules: Bluegiga BLE112 and HM10

Here are the differences I could find:

HM-10:   power: 3.3v (only)
BLE-112: power: 2.0 - 3.6V -- better for coin cell operation, for example

HM-10:   28 x 13 x 2.3 mm
BLE-112: 18 x 12 x 2.3 mm  (smaller)

HM-10:   available only from China  ($6.05, e.g. www.fasttech.com)
BLE-112: available from US distributors (Digi-Key & Mouser, $15.66)

HM-10:   must be controlled by AT commands (requires separate µC)
BLE-112: can run code directly on device (8051), or controlled via AT coimmands

HM-10:   GPIO interface
BLE-112: UART, USB host, SPI, I2C, PWM, 12-bit ADC, GPIO interfaces

HM-10:   max transmit power: +6 dBm (better)
BLE-112: max transmit power: +3 dBm

HM-10:   sleep current: 400 uA to 1.5 mA
BLE-112: sleep current: 0.4 uA (1000 x better)

HM-10:   speed: 48 Kbps
BLE-112: speed: 100 Kbps

HM-10:   range (line of sight): 100 meteres
BLE-112: range (line of sight): 150 meteres

The HM-10 comes out better on price and slightly higher transmit power. The BLE-112 comes out better on all other measures.

The HM-10 document you linked to said the HM-10 had FCC and CE certification. However when I tried to follow the links to find the FCC ID's, there was no information. The FCC and CE certifications for the BLE-112 are on the Bluegiga site.

The BLE-113 is similar to the BLE-112, except it is 1/3 smaller (16 x 9 x 2.1), draws less power, and uses the CC2541 instead of the CC2540. However the BLE-113 has slightly lower transmit power (max 0 dBm) and a reduced range of 100 meters. The BLE-113 also deosn't have the USB interface (all the others are the same as the BLE-112). At $13.45, the BLE-113 is slightly cheaper than the BLE-112.

Electronic – run custom firmware on a pre-certified RF module without needing to redo full FCC certification

It has been my experience that you would have to re-certify if you are replacing the firmware in the module.

Be aware that despite the pre-certified nature of certain modules that ultimately you or your company are responsible for meeting the legal requirements for emissions and immunity of the product as a whole. So even though a module may be pre-certified you still need to test your system with the module present.

The only place I know of where a pre-certified type module may have some decided advantages are as follows:

For an embedded module you at least know that the pre-certified module is much less likely to be the source of issues for your system.
A module like an analogue telephone line modem that probably carries several pre-certs may excuse you from testing the analogue phone line requirements whereas the emissions and immunity part may need to still be qualified with your system as a whole.
Externally applied attachments to your product such as power bricks and cords can come pre-certified and safety inspection labeled such that you do not have to deal with that over again for your product. (A very common reason so many products today have external power bricks or wall warts).

Best Answer

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