Bluetooth TripWire -- Your "Best" Office Companion (Guide&Code)

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Hi if you haven’t watched the demo video, feel free the play this :point_up: short clip to see what it’s capable of.

Introduciton

This project took the inspiration from the another open-source project daytripper (link) which uses 2 seperate devices to detect movement and control your PC to switch Apps. However, I think if we go with the Computer Vision solution instead, we might reduce the number of hardware to just 1, and we can even push it a little further by adding some more cool features like face recognition, speed detection and even more.

That’s how I came up with this idea – using OpenMV, which is littler and easier to deploy, and a IoT Microcontroller, in this case Ameba RTL8722DM_MINI, together we can achieve the same function as daytripper and more.


Components

  1. Ameba RTL8722DM_MINI dev board x1
  2. OpenMV(any model) dev board x1

Connection is simple, just connect P0 pin on OpenMV to pin 9 on Ameba


Function Flow

This is how it works, :point_down:

image


Code

OpenMV

# Advanced Frame Differencing Example
#
# This example demonstrates using frame differencing with your OpenMV Cam. This
# example is advanced because it preforms a background update to deal with the
# backgound image changing overtime.

import sensor, image, pyb, os, time
from pyb import Pin

p_out = Pin('P0', Pin.OUT_PP)
p_out.low()

TRIGGER_THRESHOLD = 5

BG_UPDATE_FRAMES = 50 # How many frames before blending.
BG_UPDATE_BLEND = 128 # How much to blend by... ([0-256]==[0.0-1.0]).

sensor.reset() # Initialize the camera sensor.
sensor.set_pixformat(sensor.RGB565) # or sensor.RGB565
sensor.set_framesize(sensor.QVGA) # or sensor.QQVGA (or others)
sensor.skip_frames(time = 2000) # Let new settings take affect.
sensor.set_auto_whitebal(False) # Turn off white balance.
clock = time.clock() # Tracks FPS.

# Take from the main frame buffer's RAM to allocate a second frame buffer.
# There's a lot more RAM in the frame buffer than in the MicroPython heap.
# However, after doing this you have a lot less RAM for some algorithms...
# So, be aware that it's a lot easier to get out of RAM issues now. However,
# frame differencing doesn't use a lot of the extra space in the frame buffer.
# But, things like AprilTags do and won't work if you do this...
extra_fb = sensor.alloc_extra_fb(sensor.width(), sensor.height(), sensor.RGB565)

print("About to save background image...")
sensor.skip_frames(time = 2000) # Give the user time to get ready.
extra_fb.replace(sensor.snapshot())
print("Saved background image - Now frame differencing!")

triggered = False

frame_count = 0
while(True):
    clock.tick() # Track elapsed milliseconds between snapshots().
    img = sensor.snapshot() # Take a picture and return the image.

    frame_count += 1
    if (frame_count > BG_UPDATE_FRAMES):
        frame_count = 0
        # Blend in new frame. We're doing 256-alpha here because we want to
        # blend the new frame into the backgound. Not the background into the
        # new frame which would be just alpha. Blend replaces each pixel by
        # ((NEW*(alpha))+(OLD*(256-alpha)))/256. So, a low alpha results in
        # low blending of the new image while a high alpha results in high
        # blending of the new image. We need to reverse that for this update.
        img.blend(extra_fb, alpha=(256-BG_UPDATE_BLEND))
        extra_fb.replace(img)

    # Replace the image with the "abs(NEW-OLD)" frame difference.
    img.difference(extra_fb)

    hist = img.get_histogram()
    # This code below works by comparing the 99th percentile value (e.g. the
    # non-outlier max value against the 90th percentile value (e.g. a non-max
    # value. The difference between the two values will grow as the difference
    # image seems more pixels change.
    diff = hist.get_percentile(0.99).l_value() - hist.get_percentile(0.98).l_value()
    triggered = diff > TRIGGER_THRESHOLD

    if triggered == True:
        p_out.high()
    else:
        p_out.low()


    print(clock.fps(), triggered) # Note: Your OpenMV Cam runs about half as fast while
    # connected to your computer. The FPS should increase once disconnected.

Ameba

#include "BLEHIDDevice.h"
#include "BLEHIDKeyboard.h"
#include "BLEDevice.h"

BLEHIDKeyboard keyboardDev;
BLEAdvertData advdata;

#define ENABLE_PIN 9

void setup() {
  Serial.begin(115200);
  advdata.addFlags();
  advdata.addCompleteName("AMEBA_BLE_HID");
  advdata.addAppearance(GAP_GATT_APPEARANCE_HUMAN_INTERFACE_DEVICE);
  advdata.addCompleteServices(BLEUUID(HID_SERVICE_UUID));

  BLEHIDDev.init();

  BLE.init();
  BLE.configAdvert()->setAdvData(advdata);
  BLE.setDeviceName("AMEBA_BLE_HID");
  BLE.setDeviceAppearance(GAP_GATT_APPEARANCE_HUMAN_INTERFACE_DEVICE);
  BLE.configSecurity()->setPairable(true);
  BLE.configSecurity()->setAuthFlags(GAP_AUTHEN_BIT_BONDING_FLAG);
  BLE.configServer(3);
  BLE.addService(BLEHIDDev.hidService());
  BLE.addService(BLEHIDDev.battService());
  BLE.addService(BLEHIDDev.devInfoService());

  pinMode(ENABLE_PIN, INPUT);

  BLE.beginPeripheral();
}

int flag = 0;

void loop() {
  if (BLE.connected() && digitalRead(ENABLE_PIN) && flag == 0) {
    Serial.println("Sending keystrokes");
    keyboardDev.keyReleaseAll();
    delay(100);
    keyboardDev.keyPress(HID_KEY_ALT_LEFT);
    delay(100);
    keyboardDev.keyPress(HID_KEY_TAB);
    keyboardDev.keyReleaseAll();
    delay(100);
    flag = 1;
  } else {
    flag = 0;
    delay(100);
  }
}

Conclusion

This project is not perfect as it’s done in a rush, so if anyone wants to perfect it you may go ahead and change my code however you like, or leave a comment below if you have a question or want to discuss something with me~

Until next time, happy coding :sunglasses: