We have a bush track that arrives on the bottom of our property, on the public land. When people suddenly appear there it makes our dogs very excited, and my partner would prefer we had notice that they are arriving ahead of time, so we can control the dogs.
This same solution could also be used for a gateway / driveway to tell you people are arriving on your farm, or in fact any other Dakota Alert monitoring solution.
The aim is to connect our Dakota Alert monitor to a raspberry pi, and then in turn connect that to a push alerting application that puts alerts onto your mobile phone when someone is coming. From there, if you have a smart watch your phone will alert on your smart watch.
The Dakota Alert equipment can be found here: https://dakotaalert.com/. You need a module that has the relay outputs – in our case the 4000 plus kit. This kit can trigger a relay when someone arrives, as well as playing a tone. That trigger is then read by the raspberry pi. This unit has a 1.6km range between the beams and the receiver unit (1 mile I guess), which is plenty for what we needed.
Start off by configuring the Dakota Alert system, and set the dip switches so that relay 1 will trigger. Get someone to walk through the beam and check that you’re getting a signal on the relay output (you can do this with a continuity tester, or using your multimeter to check the resistance – it should go to zero on the normally open connections when someone goes through the beam).
Next, you need a Raspberry Pi. Install it with Raspberry Pi OS (raspbian), and get it connected to your network and operating. There are plenty of guides on the internet to do that. We’re going to connect the Dakota Alert system to the GPIO pins on the Raspberry Pi. You need to know which Pi you have – I have an old Raspberry Pi model A, but you may have a newer one, and the pins can be slightly different. Refer to the pinout here.
What we’ll do is to take a line from the 3V3 (3.3V) power output on the pi, through the switch on the Dakota Alert, and back to the GPIO pin you’ve chosen on the pi (in my case, I’m going to GPIO11, or pin 23). That looks something like this:
What you can see here is the red wire coming from pin 1 on the Raspberry Pi (marked as 3V3 in the pinout). It then goes to the NO (normally open) connection for relay 1 on the Dakota Alert Receiver (you press the orange tab in with a screwdriver to put the wire in). Then we come back out of the common on the NO relay 1 switch, and back to pin 23 on the Pi (GPIO pin 11).
The effect of this is that we’re taking 3.3V from the Pi, running it through the relay switch on the Dakota Alert receiver, and back to Pin 11. When the Dakota Alert relay switch is open (remembering it’s “normally open”) then we have no voltage. When the Dakota Alert relay switch closes (when someone comes) then it will put 3.3V on GPIO pin 11.
You can test this directly on the Pi with the following commands:
pi@raspberrypi4:~ $ cd /sys/class/gpio
pi@raspberrypi4:/sys/class/gpio $ ls
export gpiochip0 unexport
pi@raspberrypi4:/sys/class/gpio $ echo 11 > export
pi@raspberrypi4:/sys/class/gpio $ ls
export gpio11 gpiochip0 unexportThis makes the pin gpio11 available for direct manipulation.
pi@raspberrypi4:/sys/class/gpio $ cd gpio11
pi@raspberrypi4:/sys/class/gpio/gpio11 $ ls
active_low device direction edge power subsystem uevent value
pi@raspberrypi4:/sys/class/gpio/gpio11 $ echo in > direction
pi@raspberrypi4:/sys/class/gpio/gpio11 $ cat value
0The value is currently 0, meaning no voltage. If you trigger your Dakota Alert by having someone else walk through the beam, and cat value whilst they do it, you should see the value change to 1. If it doesn’t then you need to do some trouble shooting.
You now have your Dakota Alert system connected to your pi, and telling your pi when someone crosses the beam.
Next, you need to install a push alert app on your phone, so that you can receive alerts. There are a number of different apps available, but I chose pushover, as it seemed the most simple and did exactly what I wanted and nothing more. Follow the instructions on their site to create a userid, download the app, and install it on your phone. Get to a point where you can send alerts to yourself on your phone through their website or by using the e-mail.
Next, create an application on the pushover site, and get the API token from that new application.
Next, we’re going to write a python script that listens for the Dakota Alert relay on the GPIO pins, and then calls pushover to tell it that an alert has been recieved.
I initially wrote this code using information from this alarm howto, and modified it using information from this robotics tutorial, which had more elegant handling of ctrl-c through using interrupts instead of waiting on an alert.
The final code looks like this:
#!/usr/bin/python3.7
import http.client, urllib
import signal, sys, syslog, time
import RPi.GPIO as GPIO
# constant for the GPIO pin wwe've chosen
OUR_PIN = 11
# signal handler that traps ctrl-c, cleans up the GPIO, and exits
def signal_handler(sig, frame):
GPIO.cleanup()
sys.exit(0)
# callback when the pin is triggered, which calls pushover
def pin_triggered_callback(channel):
syslog.syslog("Detected a rising edge - waiting 100ms to see if we stay on")
time.sleep(0.1)
if GPIO.input(OUR_PIN) == 1:
syslog.syslog("Still high after 100ms, someone is approaching")
conn = http.client.HTTPSConnection("api.pushover.net:443")
conn.request("POST", "/1/messages.json",
urllib.parse.urlencode({
"token": "<<your pushover API/application token>>",
"user": "<<comma separated pushover users to notify>>",
"message": "Someone approaches around the track",
"sound": "alien",
}), { "Content-type": "application/x-www-form-urlencoded" })
response = conn.getresponse()
# if response isn't 200 then we failed - no actual error handling here, we just print it on the console
if response.status != 200 :
syslog.syslog("Failed to send notification for trail monitoring: " + response.status + response.reason + response.read(1000) )
else:
syslog.syslog("Wasn't sustained for 100ms, transient spike of some sort")
# main routine - sets everything up, and installs the interrupt handlers
if __name__ == '__main__':
#setup GPIO using Broadcom SOC channel numbering
GPIO.setmode(GPIO.BCM)
# set to pull-up (normally closed position)
GPIO.setup(OUR_PIN, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.add_event_detect(OUR_PIN, GPIO.RISING,
callback=pin_triggered_callback, bouncetime=2000)
signal.signal(signal.SIGINT, signal_handler)
signal.pause()
You then need to add this script to the autostart on your pi, so that when it reboots it’s automatically executed. There are a bunch of ways to do that here, I’m lazy so I’m just doing rc.local. One impact of this is that if the script crashes it won’t restart, and more complete methods could monitor it’s execution and auto-restart it.
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
printf "My IP address is %s\n" "$_IP"
fi
/home/pi/TrailMonitoring/trailMonitoring.py &
exit 0
We add in our script name with an & on the end so that it runs in the background (rather than blocking the startup script). We can see what it’s doing by looking in /var/log/syslog.
