HM-10 Bluetooth 4.0 BLE Module Introduction

First part of a comprehensive look at the HM-10.

Everything you wanted to know and more.

Introduction

The HM-10 is a small 3.3v SMD Bluetooth 4.0 BLE module based on the TI CC2540 or CC2541 Bluetooth SOC (System On Chip). The HM-10 is made by Jinan Huamao Technology and is one of many Bluetooth devices they produce.

There are 4 versions of the HM-10. The differences are usb pads and a crystal.
1 – with usb pads and the additional crystal
2 – with usb pads without the extra crystal
3 – no usb pads but with the additional crystal
4 – no usb pads, no extra crystal.

The HM-10C-A and HM-10C-B models do not have the pads along the bottom (the USB connections) and therefore, have 26 pads instead of 34 which makes it a little cheaper to produce. The B variant boards lack the external crystal, again making them a little bit cheaper. Operationally they are all the same.

HM-10 Basic specs

• Based on the CC2540 or the CC2541 chip
• +2.5v to +3.3v
• Requires up to 50mA
• Uses around 9mA when in an active state
• Use 50-200uA when asleep
• RF power: -23dbm, -6dbm, 0dbm, 6dbm
• Bluetooth version 4.0 BLE
• Default baud rate firmware before V700 is 9600
• Default baud rate firmware V700 and up is 115200
• Default PIN is 000000
• Default name is HMSoft

The latest HM-10s all appear to the the CC2541 chip. This is the same as the CC2540 except it is lower power and has a shorter range. The CC254x is based on the 8051 and runs at 32MHz.

The HM-10 is has become a very popular Bluetooth 4 BLE module for use with the Arduino. In part due to the standard UART serial connection that makes it fairly straight forward to connect to an Arduino. The UART layer is a good thing and a bad thing, it allows ease of use but it hides the BLE layer so you have no control over the actual BLE side of things. The HM-10 is Bluetooth version 4.0 only. This means it cannot connect to Bluetooth 2/2.1 modules such as the HC-06 and HC-05.

The HM-10 is controlled via AT commands which are sent over the serial UART connection. There are a host of commands, some simple, some more complex, and these are covered later.

Fakes

There are lots of comments on the internet about fake HM-10s and even Jinan Huamao includes information in the data sheets. I do not see the non-HM-10s as fakes, I see them as similar devices with different firmware. To me if they were fakes they would copy the firmware.
I think a lot of the problem comes from how the non-HM-10s are sold, especially on places like ebay and aliexpress. You will often see modules sold as HM-10s when they are in fact not. One of the easiest ways to spot the non-HM-10s was the lack of a crystal, unfortunately you can now buy actual HM-10s without the crystal so the confusion is likely to get worse.

HM-10 on a breakout board

The HM-10 is available as a small SMD module and also available mounted to a breakout board that exposes the power and UART connections to breadboard friendly male pins. The breakout board includes a 3.3v power regulator that makes them 5V compatible. This makes them ideal for hobbyists like me. You should note that the RX pin is is still 3.3v and when using a 5v Arduino you should covert the Arduino’s 5v TX to 3.3v for the HM-10 RX.

Pin	Description
STATE	Connection status LOW when not connected. HIGH when connected
VCC	Power in. 3.6v to 6v
GND	Common ground
TXD	Serial UART transmit
RXD	Serial UART receive
BRK	Break pin. When there is an active connection, bringing the BRK pin LOW breaks the connection

On board LED

The on board LED blinks when waiting for connection. It blinks half a second on, half a second off.
The LED becomes solid on when a connection is made and returns to blinking when the connection is broken.
The LED changes to solid on when pairing. After pairing it returns to flashing. It basically makes a connection to pair and so turns on the LED to show the connection status. After pairing is completed the connection is closed and the LED is turned off.

The behavior of the LED can be changed using the PIO1 command.
“AT+PIO10” – Default setting. When not connected the LED blinks 500ms on, 500ms off. When connected the LED is solid on.
“AT+PIO11” – When not connected the LED is off. When connected the LED is solid on.

STATE Pin

The STATE pin is LOW when there is no connection and goes HIGH when a connections is established.

BRK Pin

The BRK pin allows you to cancel a connection. When there is an active connection, bringing the BRK pin momentarily LOW breaks the connection. When there is no connection making the BRK HIGH or LOW has no effect. Although not strictly required, pulling the BRK pin HIGH for normal use will stop the pin floating.

Jinan Huamao Technology Website

Website: http://www.jnhuamao.cn/index.asp
Main products page: http://www.jnhuamao.cn/bluetooth.asp
Firmware downloads: http://www.jnhuamao.cn/download_rom_en.asp?id=1#
Firmware release notes: http://www.jnhuamao.cn/index_en.asp?ID=1

Bluetooth 4 information pack

As well as firmware files, there are quite a few resources available on the Huamao website:

The information pack is available by clicking on one the HM-10 images on the Huamao website Bluetooth page. Jump to the website, click on one of the HM-10 images and download the zip archive.

You can also download from here.

The zip file contains the data sheet, instructions for the self leaning mode, and other useful notes. The datasheet in the dlownload is V610/V707 2020-02.

The data sheet in the download shows V610/V707 and is not fully up-to-date; it does not include the new AT+READOF command and has the old AT+CO command. It does include AT+PACK which was introduced in v702 though. Huamao version control looks to be as good as mine…..

The readme in the archive is not up-to-date either (goes up to V605). The readme that comes with the firmware download is better. The readme that comes with firmware V710 includes up to V709.

Firmware

The latest firmware is v710 (the download link says V710 but the folder inside the zip archive is named V709) and it can be downloaded from the download centre. Go here firmware download page and then click the Firmware Download link on the left hand side.

AT Mode default baud rates keep changing. These are the baud rates used to connect to the HM-10.
Firmware prior to V700 it is 9600.
Firmware V700 to V709 it is 115200.
V710 it looks like its back to 9600.

Here are the updates/changes since V700

V710
?

V709
-Add AT+Z1 AT+Z2 AT+Z3 AT+Z4 AT+Z5 AT+Z6 command.
Those commands is used to change full advertisiment package and ScanResponse package
Please use HM_Config_Assistant.exe to get AT commands list.

V708
-Add deep sleep mode
AT+IMME1 and AT+SLEEP (or AT+PWRM0), let module into 0.1uA deep sleep mode.

V707
-Modify AT+ADDR command
AT+ADDR command used to change module MAC.
Query command AT+ADDR?
Setup command AT+ADDR
P1: 12 Bytes, MAC string.

V706
-Add AT+UART command
AT+UART command used to switch UART wake function when module in sleep mode.
P1: 1 Byte, possible value ?, 0, 1
?: Query
0: Open UART wake function (default value)
1: Close UART wake function.

V705
-Add AT+READOF command
AT+READOF?, used to read long char value
P1: 2 Bytes, Start Index.
P2: 4 Bytes, Char Handle.

V704
-Modify AT+CO command
AT+CO[P3][P4][P5], used to make connection.
P1: 1 Byte, Devie type.
P2: 12 Bytes, Device MAC
P3: 4 Bytes, Notify Handle
P4: 4 Bytes, Write Handle
P5: 2 Bytes, Write property.

P1 and P2 must be input;

V703
-Add AT+INDICA_ON command

V702
-Made wakeup function better
-Add AT+PACK command used to modify data in Advertisement package.
AT+PACK[P1][P2][P3][P4][P5][P6]
P1, P2, P3, P4, P5, P6 length all is 2.
P1, P2, P3, P4, P5, P6 value 00~FF

V701
-Add AT+SET_WAY command

V700
-Default baud rate change to 115200
-Removed AT+ANCS command
-Removed AT+COMP command
-Removed AT+128B command
-Added new function used to support different brand BLE device
-Added AT+FINDSERVICES? command
-Added AT+FINDALLCHARS? command
-Added AT+NOTIFY_ON command
-Added AT+NTOIFYOFF command
-Added AT+READCHAR command
-Added AT+CHAR command
-Added AT+READDATA command
-Added AT+READDESC command
-Added AT+SEND_DATA command

Other changes include
– the default baud rate changed to 115200
– At Mode now accepts commands with and without line endings.

There were many reports of Android 8.1 not connecting to cheap BLE modules (inluding fake HM-10s), Jinan Huamao support say that the HM-10 (original ones, not copies) are compatible with Android 8. I do not have Android 8 so have not tried and cannot confirm. For a while there was a message on their website stating HM-10s were compatibly with Android 8 but it appears the News section no longer exists.

Firmware version 5.49 is available in two versions; regular and long name. The regular firmware does not have an updated read me so I don’t know what changes, if any, have been made. The long name firmware adds, you guessed it, long names. Device names can now be up to 29 characters. At the same time the iBeacon function and the ANCS function have been removed. This looks to be a one off (later firmware do not have a long name version and unless you desperately need long names I suggest you stay with the regular firmwares.

I always had issues using the HM-10 with other modules. I never got them to fully work with modules like the BT05 and the AT09. The BT05 & AT09 could receive data from the HM-10 but not the other way round.
I emailed Jinan Huamao a few times about this and didn’t get any replies but it looks like they at least addressed the problem and since firmware V700 there has been better compatibility with other BLE modules.

Bluetooth 4 BLE

BLE is not an upgrade to Bluetooth Classic, it is a different system with different intended uses. BLE works in a very different way to the earlier Bluetooth.
BLE is designed for low energy applications and achieves this by using infrequent small packets of data. It is not really designed for continuous connections and large amounts of data. For this, Bluetooth Classic is a better choice. In essence, BLE achieves its low power consumption by not being connected very often, unlike Bluetooth Classic which maintains a constant connection.

While you can create a classic style connection using 2 HM-10s, and I give an example below, they were not designed for this and if this is all you need then you would be better suited with Bluetooth Classic modules like the HC-05s or a HC-05 and a HC-06.

There are 2 ways BLE devices can talk to each other; Broadcaster + Observer, and, Central + Peripheral. The HM-10 can use both methods.

• With Broadcaster + Observer there isn’t a standard connection, the Broadcaster, usually some kind of sensor, sends out periodic signals (advertising packets) which the Observer listens for. The Broadcaster does not normally know if anything is listening or not.
• The Central + Peripheral scenario is more like (but not exactly the same) as the classic connection. When the Central (master) device finds a Peripheral (slave) device it wants to connect to it initiates a connection and takes on the master role managing the connection and timings.

HM-10 Services and Characteristics

BLE is all about services and characteristics and like all BLE devices, the HM-10 has a set of services and each service has a set of related characteristics. Characteristics are where the values are, some are READ, some are WRITE, and some are READ and WRITE.

All the services on the HM-10 are predefined except one. This is a custom service that has one custom characteristic. Predefined services and characteristics are ones where the UUID and the name are set by the Bluetooth governing body. For example, the characteristic 0x2A00 is the device name and when a device has this characteristic it should always be the device name.

A full list of the predefined services can be found here and a list of the characteristics is here.

The HM-10 uses the custom characteristic to send and receive the data it receives over the serial UART interface. It works by setting the value of the custom characteristic to the value of the data to be transmitted. It then sends out a notification to the remote device to say there is new data available.
When you tell the the HM-10 to transmit “HELLO”, it first sets the value of the custom characteristic to “HELLO” and then it sends out a notification telling the remote device “Hey, I have new data, come and get it.” The remote device is scanning for the notifications and when it receives one it knows there is a new value, so it reads the data and then sends back a message saying “Thanks, I have it”.

The custom characteristic can hold up to 20 characters, this means to send a string longer than 20 characters the HM-10 splits the data in to 20 character segments and sends each one in turn until none are left.

SERVICE 1
UUID: 00001800-0000-1000-8000-00805F9B34FB
GENERIC ACCESS

• UUID: 00002A00-0000-1000-8000-00805F9B34FB
• DEVICE NAME
• READ

• UUID: 00002A01-0000-1000-8000-00805F9B34FB
• APPEARANCE
• READ

• UUID: 00002A02-0000-1000-8000-00805F9B34FB
• PERIPHERAL PRIVACY FLAG
• READ/WRITE

• UUID: 00002A03-0000-1000-8000-00805F9B34FB
• RECONNECTION ADDRESS
• READ/WRITE

• UUID: 00002A04-0000-1000-8000-00805F9B34FB
• PERIPHERAL PREFERRED CONNECTION PARAMETERS
• READ

SERVICE 2
UUID: 00001801-0000-1000-8000-00805F9B34FB
GENERIC ATTRIBUTE

• UUID: 00002A05-0000-1000-8000-00805F9B34FB
• SERVICE CHANGED
• INDICATE

SERVICE 3
UUID: 0000FFE0-0000-1000-8000-00805F9B34FB
CUSTOM SERVICE

• UUID: 0000FFE1-0000-1000-8000-00805F9B34FB
• CUSTOM CHARACTERISTIC
• READ/WRITE/NOTIFY

The main part of the custom service UUID (FFE0) the main part of the custom characteristic UUID (FFE1) can be changed via AT commands.
A second characteristic can also be added.

You can see the services and characteristics in action using a BLE scanner app. lets give it a try

Get Started With The HM-10

First, lets use an Android device to scan for the HM-10. Then let’s try to read the services and characteristics from the HM-10. You can also use an IOS device but you will need to find a suitable BLE scanner app.

Power on the HM-10, you can use an Arduino for this or you can simply connect 5V to HM-10 VCC and GND to HM-10 GND.

If done correctly, the LED on the HM-10 should be flashing. When a connection is established the LED will be become solid on.

Checking The HM-10 With An Android Device

Depending on your Android device and the version of Android you are running the HM-10 may or may not show up when searching for Bluetooth devices under the Android Settings.

Samsung S9 with Android 10 – Finds the HM-10
Lenovo TAB-M8 tablet running Android 10 – Finds the Hm-10

If you device does not find the HM-10 under Bluetooth settings, try using the BLE Scanner app.

To connect to the HM-10 and to read the services and characteristics we need to use a BLE app. Here I am using BLE Scanner. There are many other similar apps available such as B-BLE.

Reading the characteristics of the HM-10 using using BLE Scanner

Open the BLE Scanner app and find the HM-10. Tap the CONNECT button to get the app to connect to the HM-10 and start reading its properties.

Clicking the small down arrows will expand the services and display the characteristics.

R = Read value
W = Write Value
I = Toggle indications on and off
N = Toggle notifications on and off

Tapping one of the labels will read the characteristic value. For example, under Device Name, tapping the reads and then shows the device name value.

Under Custom Service you can see the HM-10s default service and characteristic values. You can also see that the HM-10s custom characteristic has Read, Write, and Notify attributes.

And that’s it. You are now ready for the next part, talking to the HM-10.