Opening the front door from your desk
...or from the toilet.
- Author
- Solution Seeker
- Publish date
- · 5 min read
Whenever someone rings the doorbell in our office, a loud sound is played from two door intercoms, one downstairs and one upstairs. The one that is upstairs is located near our development team. The red dot in the below image shows the location of the upstairs intercom, while the blue ellipse marks where the developers are situated.
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When we moved to our current location in june 2019 the job of answering the intercom ended up being the development team's responsibility, mainly due to their close proximity to the intercom. The doorbell rings a few times a day, and either the microphone or the speaker outside the front door is terrible, because nobody ever hears what is said in the intercom. This of course leads to nobody bothering to make an attempt at communication, and everyone just presses on the “open door” button without second thoughts.
The job of answering the door is reduced to walking a few meters from the desk to the intercom, pushing the button, and returning to the desk. This is, naturally, a tough ask for a developer. Not that the distance is overwhelming, but precious concentration is broken as soon as you get up from your desk.
The hardware solution
The unnatural solution for a software engineer is to throw hardware at the problem, yet in this case that is what we did (at first). Realizing that a button is the simplest circuitry element imaginable that just shorts the circuit it is connected to, we soldered on two wires to the back of the button which we then extended all the way to our desks.
The button in the middle of the left image is the button that opens the door, and that we soldered wires onto the back of. The gray and the white wires are the wires that extend to our desks.
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We then connected three buttons to these wires, making a parallel connection for each button, so that only one of the buttons needed to be pressed to open the door. We wanted more than one button to avoid just moving the problem from being to walk to the intercom to walking to whoever's desk the button was on.
Fire in the hole!
Now whenever someone rings the door, the door opens almost immediately, as it’s almost become a competition to press the button first (not that we have a way of determining who won).
The software solution
The above solution works well when at least one of the desks with a button is “manned”. Whenever there’s a meeting or the developers are working from home we’re back to the original problem of having to walk to the intercom to answer the door. Only this time the distance is probably much greater (the developers sit right next to the intercom) so the problem is much worse.
Thus we needed a solution that allows any employee to open the door from anywhere in the office. Extending wires to every corner of the office was quickly deemed too hardware-heavy, so a solution involving a Raspberry PI, a tiny custom circuit, and some software was devised instead.
This new solution works as such: The Raspberry is connected to the same wires the buttons are connected to, and shorts these (acting as a remote controlled button) on behalf of employees. The Raspberry hosts a very simple website with a single button that, when clicked, triggers the Raspberry to open the door.
![](https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=560&q=90&w=600&s=bc0eb306eeaf88ca74d9f0f4d2036050 600w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=653&q=90&w=700&s=b0ef8974464281bbaa5df90a21e0b0f6 700w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=746&q=90&w=800&s=024872b152736eb9d471d36c56780c7e 800w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=840&q=90&w=900&s=efed07fc70598fe0754f094d812ebff5 900w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=933&q=90&w=1000&s=19fa13b13591348d9072bfe11e649da5 1000w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1026&q=90&w=1100&s=e352b4b97dd2d22da4923b652846e096 1100w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1119&q=90&w=1200&s=6241b748cbf570f53fd0e8fe4e8205c5 1200w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1213&q=90&w=1300&s=58982665c541b2503e87b15918574fc8 1300w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1306&q=90&w=1400&s=7adc75cceb294d4afb0cacc3a42b788e 1400w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1399&q=90&w=1500&s=07125e43921d45fa2d72cb896d5486df 1500w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1493&q=90&w=1600&s=c687e3ddd1e03bf5a2eea4b238a2a221 1600w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1586&q=90&w=1700&s=471aff6c6c1b5bed1632a2090cf3c8ca 1700w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1679&q=90&w=1800&s=96e9f21b3b7b47a0cb228c1cc5dda902 1800w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1772&q=90&w=1900&s=1548160d024e2fc3343d0018210e92a1 1900w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1866&q=90&w=2000&s=34aab62deca97bc2545138654f20f54e 2000w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=1959&q=90&w=2100&s=6b812bce898400ddf05dfe2301c7ee2f 2100w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=2052&q=90&w=2200&s=3e574db7855374dbc5e564ad766a4d38 2200w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=2145&q=90&w=2300&s=dbe49a13734b3c9402a8fc18e4ee131c 2300w, https://solutionseeker2021.imgix.net/images/old/image-05.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=2239&q=90&w=2400&s=855868d21d43a557696e0bcd03f6690f 2400w)
Custom circuit
The custom circuit is needed to be able to short the wires, which the Raspberry can’t do out of the box (it can only pull the voltage up or down). The custom circuit consists of an NPN transistor and a resistor. The base of the transistor is connected to a GPIO pin on the Raspberry, and the collector and emitter are connected to the wires that extend from the intercom. This way, when the GPIO on the Raspberry is high, the transistor shorts the wires in the same way a button would, while when the GPIO is low, the transistor acts as an open circuit.
![](https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=225&q=90&w=600&s=44869b9557fdc43e828c5580b201184e 600w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=263&q=90&w=700&s=6bfd4b8215e3f0d30648adb7fe7ea9f4 700w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=300&q=90&w=800&s=9983128c461c5d52b1df7414947f8c72 800w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=338&q=90&w=900&s=4a1c45b526f033010bcd4df70ea52df8 900w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=375&q=90&w=1000&s=6c56fd8ec45d53e377f8df8d337e2cd6 1000w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=413&q=90&w=1100&s=b5f1d90a3689fbb4155155bf9272ede2 1100w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=450&q=90&w=1200&s=3202a9a932cff0f70457117ea80b7ad4 1200w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=488&q=90&w=1300&s=2445af76085e48962b0a085af05fcdfa 1300w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=525&q=90&w=1400&s=fff65ac1c6c94c57d0214e4a5791126b 1400w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=563&q=90&w=1500&s=c6bd0437fe09455574d10aea49b1b9e0 1500w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=600&q=90&w=1600&s=f237de29ffd4f760a2b240d89a3e6d42 1600w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=638&q=90&w=1700&s=c22cccf8d69dd2c23e21aa61799d782e 1700w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=675&q=90&w=1800&s=07ad80036d1d15c6d49e9c37f5b0f29f 1800w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=713&q=90&w=1900&s=835a8a1028e153da7bcd7be41f7e440e 1900w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=750&q=90&w=2000&s=71f28e67a16495e92cac54c4320a1f40 2000w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=788&q=90&w=2100&s=e96b425c39ffb73e304f5749ec988881 2100w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=825&q=90&w=2200&s=86beb06b605cc3307f46dca3d5031dd1 2200w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=863&q=90&w=2300&s=960d3ff6b929a361cc358d0ea53e48dc 2300w, https://solutionseeker2021.imgix.net/images/old/image-06.png?auto=compress%2Cformat&crop=focalpoint&cs=srgb&fit=crop&fp-x=0.5&fp-y=0.5&h=900&q=90&w=2400&s=bba4a3bff3d4bc9b7822b12c2aaa194c 2400w)
Software
The software consists of two Python applications: One for setting the GPIO pin high, wait a few seconds, and setting it low again. The other application is a Flask application serving the website through uWSGI and nginx. The latter also handles calling the former whenever the button is pressed.
The website button name “Ofen door” is a reference to a very popular commercial in Norway (we highly recommend watching it - the humor isn’t lost on non-Norwegians): https://www.youtube.com/watch?v=sgJLpuprQp8
End comments
The solution described here has become an integral part of the infrastructure in the office. Without it, the concentration of many people would’ve been disturbed every day, and a lot of long walks to and from the intercom would be necessary. As a plus, since opening the door now only requires a WiFi connection, it is also possible to enter the office from the street using your phone instead of the physical key (we’re aware of the security implications).