This a simple demo for DJI Onboard SDK Transparent Transmission function. Also I run this demo on a Raspberry Pi.

I make this demo to detect PM 2.5 in air. And I believe everyone can obtain his/her own sensor data in the same way.

First, Pi gets sensor data from a PM 2.5 sensor. (I bought one from Taobao, which contains a USB-TTL moudel)

Second, Pi sends the data to M100 for Transparent Transmission.

Finially, the data shows on my phone or pad which is connected with M100's controllor.

Fly your M100 with RPi instead of expensive NUC !
Also Fly your M100 with your own sensors too !

• M100
• Raspberry Pi
• PM2.5 Sensor

As we know, RPi has a serial port with 3.3V. We can use it directly, so there is no need to purchase a USB-TTL model.

Here is the definition of M100's serial port.

And this is the definition of RPI's serial port.

The connection looks like this.

1. edit cmdline.txt

sudo nano /boot/cmdline.txt
change
dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait
into
dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait

2. edit inittab

sudo nano /etc/inittab
Invaild the last line #T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

In addition, to use this serial port within 230400 baudrate, we need to change uart clock.

edit config.txt sudo nano /boot/config.txt
Add this in last init_uart_clock=64000000

At last, restart your Pi and we can use /dev/ttyAMA0 to communicate with M100.

My PM2.5 sensor is driven by a arduino, so this part is sample. I just install arduino for RPi, then I can find my sensor which is /dev/ttyUSB0

In other cases, this part depends your specific sensors.

I use DJI_LIB to develop the Onboard Part. All I need to do is call relative function to init Onboard SDK and send my data.

PM25.cpp is interface of my PM2.5 sensor, developers can use yourselves code instead.

BTW: you can find DJI_LIB in Samples of DJI Onboard SDK.

1. Modify Makefile to add DJI_LIB in your progject. (You can refer to Makefile in this project)

2. Init Onboard SDK

if(Pro_Hw_Setup("/dev/ttyAMA0", 230400) < 0)      /* Open RPi <-> DJI Serial Port */
{
    perror( "UAV Serial Port Open ERROR" );
    return 0;
}
DJI_Pro_Setup(NULL);

3. Init PM25 (Change it into your sensor interface)

if(init_pm25("/dev/ttyUSB0", 2400) <0)            /* Open RPi <-> PM25 Serial Port */
{
    perror( "PM25 Serial Port Open ERROR" );
    return 0;
}

4. Activation
Just need to edit key_buf, app_id and app_level.
For Transparent-Transmission, either level 1 or level 2 is ok.

activate_data_t user_act_data;

void activation()
{

    char key_buf[65] = "input your key";   /* Input your app_key */
    char app_bundle_id[32] = "1234567890";

    user_act_data.app_id = id;                     /* Input your app_id */
    user_act_data.app_api_level = level;                    /* Input your app_level */
    user_act_data.app_ver = 0x02030A00; 
    user_act_data.app_key = key_buf;  
    strcpy((char*)user_act_data.app_bundle_id, app_bundle_id);

    DJI_Pro_Activate_API(&user_act_data,cb_fun);
}

5. Loop

Get pm25 data and call sdk function to send it.

    while(1)
    {
        if(run_flag)
        {
            int nbyte;
            nbyte = read_pm25(buffer, 1024);
            if (nbyte > 0) 
            {
                transparent_transission_send((uint8_t*)buffer, nbyte);
                //printf("%s", buffer);
            } 
        }
        sleep(1);
    }

Transparent-Transmission Send

void transparent_transission_send(uint8_t* pbuf, uint16_t len)
{   
    DJI_Pro_App_Send_Data(0 , 0, MY_ACTIVATION_SET, 0xFE, pbuf, len,NULL,0,1);                                        
    //printf("[send_data],send len %d data %s\n", len, pbuf);
}

Transparent-Transmission Receive
First, register Transparent-Transmission callback function.

DJI_Pro_Register_Transparent_Transmission_Callback(transparent_transission_receive);

Then, implement the callback function.
Here is a simple interactive cmd list.

void transparent_transission_receive(unsigned char *buf,unsigned char len)
{
    unsigned char cmd;
    cmd = buf[0];

   // printf("[recv_data],send len %d data %s\n", len, buf);

    switch(cmd)
    {
        case 'a':   
            activation();
            break;
        case 'b':
            run_flag = true;
            break;
        case 'c':
            run_flag = false;
            break;
        default:
            break;
    }
}

Import the DJI_SDK_Android_Transparent_Trasmit code tu your Android studio or Eclipes.

The following code shows you how to send and receive data.

send data:

int16_t sdk_pure_transfer_hander(uint8_t* pbuf, uint16_t len)    
{                                                                                         
   if ("" != mSendOnBoardEdit.getText().toString()){
                    DJIDrone.getDjiMC().sendDataToExternalDevice(mSendOnBoardEdit.getText().toString().getBytes(),new DJIExecuteResultCallback(){
                        @Override
                        public void onResult(DJIError result)
                        {
                            // TODO Auto-generated method stub
                        }
                    });
                    Log.d(TAG, "Submit1");
                }                                         
}

receive data:

mExtDevReceiveDataCallBack = new DJIMainControllerExternalDeviceRecvDataCallBack() {
            @Override
            public void onResult(final byte[] data)
            {
                // TODO Auto-generated method stub
                StringBuffer sb = new StringBuffer();
                sb.append(getString(R.string.external_device_recv_data)).append("\n");
                sb.append(new String(data)).append("\n");

                McRecvOnBoard = sb.toString();

                SelectDroneTypeActivity.this.runOnUiThread(new Runnable(){

                    @Override
                    public void run()
                    {
                        mRecvTextView.setText(McRecvOnBoard);
                    }
                });
            }
        };
        //设置回调接口
        DJIDrone.getDjiMC().setExternalDeviceRecvDataCallBack(mExtDevReceiveDataCallBack);

copy pm25 folder into your Pi. Then execute the following cmd. cd cmake
make
cd ../output
./pm25
The terminal should be like this.

Acttivation Successfully

0.0,25.0,59.8
[pure_transfer],send len 15 data 0.0,25.0,59.8

0.5,25.0,59.8
[pure_transfer],send len 15 data 0.05,25.0,59.8

0.9,25.0,59.8
[pure_transfer],send len 15 data 0.9,25.0,59.8

Run the App by Mobile device.
This is a sample App, but you can see the date has been received.