During the holiday season 2017 I decided to realize a long held wish for a project: an elevator controlled by my own programming.
So I built an elevator controlled with my Raspberry Pi. See description and photo’s below.
The PIXEL desktop is new in the currently latest release of Raspbian Jessie that had been designed to make the Raspberry Pi a computer you can work with on a daily basis.
At the bottom of the construction we find the controlling electronics. First of all, humbly on the right sits the Raspberry Pi, at this time with it’s Explorer HAT.
A little bit to the left we see kind of a switchboard where all cables will be wired, for the motor and for four switches, one for every floor.
Finally we take a closer look at the Raspberry Pi that will be controlling the lot using the functions of the Explorer HAT Pro (only the motor is connected so far).
In my previous post I described that I was using the Explorer HAT for the Raspberry Pi and was not entirely satisfied with the way switches were handled. I got all kinds of bounce, sometimes more than twenty reported switches, when I only pressed once… This became a real nuisance. In hindsight this might have been due to programming, but anyway…
I also downloaded the pigpio library (Pi GPIO – General Purpose Input Output) for python on the Raspberry Pi. This is a magnificent piece of work by Joan. It runs as a compiled background process (pipgiod) and services the requests from python (or C or C++ for that matter) to the GPIO system. This setup makes it really fast The pigpio library does give us the opportunity to use interrupt handlers, so our own processing can continue while the GPIO ports are being monitored by the pigpiod background process. When this detects a key-press, it activates our handler to do something with that keypress.
In the third version (February 3, 2017) I introduced a message broker to have the program “elevator_remote.py” communicate with the actual “elevator.py” program that controls the Raspberry Pi and the elevator hardware. I used the Mosquitto (mqtt) library, a fairly simple but sturdy message broker, and the paho.mqtt python library. Have a look at the overhauled code on Github.
A sample of a short session of the elevator (description below):
As you can see in the help information, an entry of 1-2 means: “I am standing at floor 1 and I want to go to floor 2“. In this session log you can see the cabin going from the first to the second floor. Then another request comes in, 3-1. The cab is at floor two, so the first thing it does is go up to floor three, wait for a short while, and then descends to the first floor as requested. Lots of requests can be entered while the elevator is working – going up or down – and they all will be handled FCFS at this time (First Come First Serve, a well known simple scheduling mechanism).
Okay, it’s not very life like, but that is not a requirement with models…
Control, indicator LED’s
Today I decided to make my code available on GitHub. When you go there you can see all the code I used. Github is a developers website where you can find large collections of repositories. The non-standard python libraries I used in this project are on there as well.
I made one little addition to the project: I removed the ‘power-LED’ and added four (blue) LED’s indicating the floor the cabin is at (yes, it’s at the first floor now):
I would like to expand on this with other scheduling mechanisms, like STTF (Shortest Trip Time First), SCAN (just go up and down and process every request we encounter for the same direction) and perhaps even more elaborate schemes.
—–===== But for now, I’m happy with how this works! =====—–