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Person detection example

This example shows how you can use Tensorflow Lite to run a 250 kilobyte neural network to recognize people in images captured by a camera. It is designed to run on systems with small amounts of memory such as microcontrollers and DSPs.

Table of contents

Running on Arduino

The following instructions will help you build and deploy this sample to Arduino devices.

The sample has been tested with the following device:

You will also need the following camera module:


Connect the Arducam pins as follows:

Arducam pin name Arduino pin name
CS D7 (unlabelled, immediately to the right of D6)
GND GND (either pin marked GND is fine)
VCC 3.3 V

Install the Arduino_TensorFlowLite library

Download the current nightly build of the library:

This example application is included as part of the official TensorFlow Lite Arduino library. To install it, open the Arduino library manager in Tools -> Manage Libraries... and search for Arduino_TensorFlowLite.

Install other libraries

In addition to the TensorFlow library, you'll also need to install two libraries:

  • The Arducam library, so our code can interface with the hardware
  • The JPEGDecoder library, so we can decode JPEG-encoded images

The Arducam Arduino library is available from GitHub at To install it, download or clone the repository. Next, copy its ArduCAM subdirectory into your Arduino/libraries directory. To find this directory on your machine, check the Sketchbook location in the Arduino IDE's Preferences window.

After downloading the library, you'll need to edit one of its files to make sure it is configured for the Arducam Mini 2MP Plus. To do so, open the following file:


You'll see a bunch of #define statements listed. Make sure that they are all commented out, except for #define OV2640_MINI_2MP_PLUS, as so:

//Step 1: select the hardware platform, only one at a time
//#define OV2640_MINI_2MP
//#define OV3640_MINI_3MP
//#define OV5642_MINI_5MP
#define OV2640_MINI_2MP_PLUS
//#define OV5642_MINI_5MP_PLUS
//#define OV5640_MINI_5MP_PLUS

Once you save the file, we're done configuring the Arducam library.

Our next step is to install the JPEGDecoder library. We can do this from within the Arduino IDE. First, go to the Manage Libraries... option in the Tools menu and search for JPEGDecoder. You should install version 1.8.0 of the library.

Once the library has installed, we'll need to configure it to disable some optional components that are not compatible with the Arduino Nano 33 BLE Sense. Open the following file:


Make sure that both #define LOAD_SD_LIBRARY and #define LOAD_SDFAT_LIBRARY are commented out, as shown in this excerpt from the file:

// Comment out the next #defines if you are not using an SD Card to store the JPEGs
// Commenting out the line is NOT essential but will save some FLASH space if
// SD Card access is not needed. Note: use of SdFat is currently untested!

//#define LOAD_SD_LIBRARY // Default SD Card library
//#define LOAD_SDFAT_LIBRARY // Use SdFat library instead, so SD Card SPI can be bit bashed

Once you've saved the file, you are done installing libraries.

Load and run the example

Go to File -> Examples. You should see an example near the bottom of the list named TensorFlowLite. Select it and click person_detection to load the example. Connect your device, then build and upload the example.

To test the camera, start by pointing the device's camera at something that is definitely not a person, or just covering it up. The next time the blue LED flashes, the device will capture a frame from the camera and begin to run inference. Since the vision model we are using for person detection is relatively large, it takes a long time to run inference—around 19 seconds at the time of writing, though it's possible TensorFlow Lite has gotten faster since then.

After 19 seconds or so, the inference result will be translated into another LED being lit. Since you pointed the camera at something that isn't a person, the red LED should light up.

Now, try pointing the device's camera at yourself! The next time the blue LED flashes, the device will capture another image and begin to run inference. After 19 seconds, the green LED should light up!

Remember, image data is captured as a snapshot before each inference, whenever the blue LED flashes. Whatever the camera is pointed at during that moment is what will be fed into the model. It doesn't matter where the camera is pointed until the next time an image is captured, when the blue LED will flash again.

If you're getting seemingly incorrect results, make sure you are in an environment with good lighting. You should also make sure that the camera is oriented correctly, with the pins pointing downwards, so that the images it captures are the right way up—the model was not trained to recognize upside-down people! In addition, it's good to remember that this is a tiny model, which trades accuracy for small size. It works very well, but it isn't accurate 100% of the time.

We can also see the results of inference via the Arduino Serial Monitor. To do this, open the Serial Monitor from the Tools menu. You'll see a detailed log of what is happening while our application runs. It's also interesting to check the Show timestamp box, so you can see how long each part of the process takes:

14:17:50.714 -> Starting capture
14:17:50.714 -> Image captured
14:17:50.784 -> Reading 3080 bytes from ArduCAM
14:17:50.887 -> Finished reading
14:17:50.887 -> Decoding JPEG and converting to greyscale
14:17:51.074 -> Image decoded and processed
14:18:09.710 -> Person score: 246 No person score: 66

From the log, we can see that it took around 170 ms to capture and read the image data from the camera module, 180 ms to decode the JPEG and convert it to greyscale, and 18.6 seconds to run inference.

Running on SparkFun Edge

The following instructions will help you build and deploy this sample on the SparkFun Edge development board. This sample requires the Sparkfun Himax camera for the Sparkfun Edge board. It is not available for purchase yet.

If you're new to using this board, we recommend walking through the AI on a microcontroller with TensorFlow Lite and SparkFun Edge codelab to get an understanding of the workflow.

Compile the binary

The following command will download the required dependencies and then compile a binary for the SparkFun Edge:

make -f tensorflow/lite/micro/tools/make/Makefile TARGET=sparkfun_edge person_detection_bin

The binary will be created in the following location:


Sign the binary

The binary must be signed with cryptographic keys to be deployed to the device. We'll now run some commands that will sign our binary so it can be flashed to the SparkFun Edge. The scripts we are using come from the Ambiq SDK, which is downloaded when the Makefile is run.

Enter the following command to set up some dummy cryptographic keys we can use for development:

cp tensorflow/lite/micro/tools/make/downloads/AmbiqSuite-Rel2.2.0/tools/apollo3_scripts/ \

Next, run the following command to create a signed binary:

python3 tensorflow/lite/micro/tools/make/downloads/AmbiqSuite-Rel2.2.0/tools/apollo3_scripts/ \
--bin tensorflow/lite/micro/tools/make/gen/sparkfun_edge_cortex-m4/bin/person_detection.bin \
--load-address 0xC000 \
--magic-num 0xCB \
-o main_nonsecure_ota \
--version 0x0

This will create the file main_nonsecure_ota.bin. We'll now run another command to create a final version of the file that can be used to flash our device with the bootloader script we will use in the next step:

python3 tensorflow/lite/micro/tools/make/downloads/AmbiqSuite-Rel2.2.0/tools/apollo3_scripts/ \
--load-address 0x20000 \
--bin main_nonsecure_ota.bin \
-i 6 \
-o main_nonsecure_wire \
--options 0x1

You should now have a file called main_nonsecure_wire.bin in the directory where you ran the commands. This is the file we'll be flashing to the device.

Flash the binary

Next, attach the board to your computer via a USB-to-serial adapter.

Note: If you're using the SparkFun Serial Basic Breakout, you should install the latest drivers before you continue.

Once connected, assign the USB device name to an environment variable:

export DEVICENAME=put your device name here

Set another variable with the baud rate:

export BAUD_RATE=921600

Now, hold the button marked 14 on the device. While still holding the button, hit the button marked RST. Continue holding the button marked 14 while running the following command:

python3 tensorflow/lite/micro/tools/make/downloads/AmbiqSuite-Rel2.2.0/tools/apollo3_scripts/ \
-r 1 \
-f main_nonsecure_wire.bin \
-i 6

You should see a long stream of output as the binary is flashed to the device. Once you see the following lines, flashing is complete:

Sending Reset Command.

If you don't see these lines, flashing may have failed. Try running through the steps in Flash the binary again (you can skip over setting the environment variables). If you continue to run into problems, follow the AI on a microcontroller with TensorFlow Lite and SparkFun Edge codelab, which includes more comprehensive instructions for the flashing process.

The binary should now be deployed to the device. Hit the button marked RST to reboot the board. You should see the device's four LEDs flashing in sequence.

Debug information is logged by the board while the program is running. To view it, establish a serial connection to the board using a baud rate of 115200. On OSX and Linux, the following command should work:

screen ${DEVICENAME} 115200

To stop viewing the debug output with screen, hit Ctrl+A, immediately followed by the K key, then hit the Y key.

Run the tests on a development machine

To compile and test this example on a desktop Linux or MacOS machine, download the TensorFlow source code, cd into the source directory from a terminal, and then run the following command:

make -f tensorflow/lite/micro/tools/make/Makefile

This will take a few minutes, and downloads frameworks the code uses like CMSIS and flatbuffers. Once that process has finished, run:

make -f tensorflow/lite/micro/tools/make/Makefile test_person_detection_test

You should see a series of files get compiled, followed by some logging output from a test, which should conclude with ~~~ALL TESTS PASSED~~~. If you see this, it means that a small program has been built and run that loads a trained TensorFlow model, runs some example images through it, and got the expected outputs. This particular test runs images with a and without a person in them, and checks that the network correctly identifies them.

To understand how TensorFlow Lite does this, you can look at the TestInvoke() function in It's a fairly small amount of code, creating an interpreter, getting a handle to a model that's been compiled into the program, and then invoking the interpreter with the model and sample inputs.

Debugging image capture

When the sample is running, check the LEDs to determine whether the inference is running correctly. If the red light is stuck on, it means there was an error communicating with the camera. This is likely due to an incorrectly connected or broken camera.

During inference, the blue LED will toggle every time inference is complete. The orange LED indicates that no person was found, and the green LED indicates a person was found. The red LED should never turn on, since it indicates an error.

In order to view the captured image, set the DUMP_IMAGE define in  This causes the board to log raw image info to the console. After the board has been flashed and reset, dump the log to a text file:

screen -L -Logfile <dump file> ${DEVICENAME} 115200

Next, run the raw to bitmap converter to view captured images:

python3 -r GRAY -i <dump file>

Training your own model

You can train your own model with some easy-to-use scripts. See for instructions.

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