I’m essentially lazy. After installing a gate on the end of the driveway, we quickly tired of getting out of the car to open and then close the gate behind us. I bought a gate actuator which came with a couple of linear actuators and a controller. Since we don’t have wired power out there, I also needed a battery and solar panel plus charge controller.

The charge controller it came with was shit and the panel was too small, so I bought a new panel and charge controller. That solved that problem. No longer getting ‘Low Voltage’ warnings from the gate controller.

The next problem was access for friends. See the article https://www.beer.org/blog/index.php/2022/07/03/playing-with-fiducials/

Another annoyance was that if we were expecting a friend or courier or other, we had to walk down the driveway with a remote, and after getting close enough to the gate, press a combination of buttons in order for the gate to open and stay open.  Then before bedtime, we had to remember to walk down the driveway to close the gate which is particularly disquieting in the dark where a hundred reflective eyeballs are looking at you from the surrounding forest.  There was also no way to know whether the gate was actually open or closed without also going for a walk.

To help address this last annoyance, I added a VHF radio module connected to a BLE dongle and a relay module with a set of ADCs to read the limit switches.  A bit of Micropython and I could send queries to the dongle to get the state of the limit switches, and press buttons remotely.  Add in some MQTT handling and I have a link to HomeAssistant.

Unfortunately, now I have 2 boxes mounted out by the gate, one with the clunky COTS gate controller+battery, and another with the barnacles that I added to the system:

There must be a better way.  The heart of the system is the COTS controller board which is really just a couple of H bridges, some current sensing, limit switch inputs and push button inputs.  Time to start experimenting.

As part of some tinkering I was doing with my robotics team, I was learning about AprilTags.  Coincidentally, I had also recently installed a gate opener at the front gate and was struggling with how to organize guest access.

I grabbed my OpenMV camera, a spare buck/boost converter, and an old Axis surveillance camera housing.  Put it all together and mounted it to a post in front of the gate:

{
  "error": "deleted_client",
  "error_description": "The OAuth client was deleted."
}

I played with the QR Code recognition and various families of AprilTag. While the QR Code recognition worked fine and allowed me some nice flexibility in terms of content, it was more fallible under varying light conditions. AprilTags are more robust and recognized pretty quickly from a few feet away.

The code is simple:

import sensor, image, time, math, omv, utime
import pyb
import machine


thresholds = ( 150,255 )
sensor.reset()                      # Reset and initialize the sensor.
sensor.set_pixformat(sensor.GRAYSCALE)
sensor.set_framesize(sensor.QQVGA)
sensor.set_auto_gain(False)
sensor.set_auto_whitebal(False)
sensor.skip_frames(time = 2000)     # Wait for settings take effect.
clock = time.clock()                # Create a clock object to track the FPS.

tag_families = image.TAG36H11|image.TAG36H11

last_tag = 0
tag_repeat_cnt = 0
tag_repeat_threshold = 5
rtc = pyb.RTC()

def set_rtc(epoch):
    dt=time.localtime(int(epoch))
    rtc.datetime(tuple(dt))


P1_PIN="P4"
P2_PIN="P5"
p1 = 0
p2 = 0

STATE_NORMAL=0
STATE_STAY_OPEN=1
STATE_STAY_CLOSED=2

state = 0
rtc_valid = 0

red_led = pyb.LED(1)
green_led = pyb.LED(2)
blue_led = pyb.LED(3)
ir_leds = pyb.LED(4)

# micropython Epoch is 2000-01-01.  My timezone is UTC+8.
epoch_fixup=946728000


def set_p1(dur=0):
    p1.low()
    red_led.on()
    time.sleep_ms(dur)
    p1.high()
    red_led.off()


def set_p2(dur=0):
    p2.low()
    green_led.on()
    red_led.on()
    if (dur == 0):
        return
    time.sleep_ms(dur)
    p2.high()
    green_led.off()
    red_led.off()

def init_gpios():
    p1=pyb.Pin(P1_PIN, pyb.Pin.OUT_PP, pyb.Pin.PULL_DOWN)
    p2=pyb.Pin(P2_PIN, pyb.Pin.OUT_PP, pyb.Pin.PULL_DOWN)
    p1.high()
    p2.high()

    return p1,p2

p1,p2 = init_gpios()
blue_led.on()

i=0
while True:
    if i > 10:
        sensor.sleep(True)
        time.sleep_ms(500)
        sensor.sleep(False)
        i = 0
    i = i+1

    img = sensor.snapshot()         # Take a picture and return the image.
                                    # to the IDE. The FPS should increase once disconnected.
    tag_list = []

    try:
        tag_list.extend(img.find_apriltags(families=tag_families))
    except (MemoryError, OSError):
        pass

    for tag in tag_list:
        if tag.id() == last_tag:
            tag_repeat_cnt = tag_repeat_cnt + 1
        else:
            tag_repeat_cnt = 0
            last_tag = tag.id()

        if tag_repeat_cnt > tag_repeat_threshold:
            if tag.id() > 1 and tag.id() < 100 and state==STATE_NORMAL:
                print("Access granted (FRIEND): {}".format(tag.id()))
                set_p1(1000)

Obviously this isn’t super secure but most people who are breaking into houses aren’t sophisticated enough to know about Fiducials. Most people will assume the camera is for someone in the house to remotely activate a switch. I am actually using somewhat different code.

Because the only power I have out there is the deep cycle battery running the gate controller, I put the OpenMV to sleep for 1/2 second at a time. Seems to do ok and has gotten through an entire winter with temps that fell to -40C.