{"id":820,"date":"2015-10-26T21:45:58","date_gmt":"2015-10-27T04:45:58","guid":{"rendered":"http:\/\/www.partofthething.com\/thoughts\/?p=820"},"modified":"2015-12-07T12:19:09","modified_gmt":"2015-12-07T20:19:09","slug":"data-acquisition-and-live-plotting-over-the-network-with-a-raspberry-pi-and-python","status":"publish","type":"post","link":"https:\/\/partofthething.com\/thoughts\/data-acquisition-and-live-plotting-over-the-network-with-a-raspberry-pi-and-python\/","title":{"rendered":"Data acquisition and live-plotting over the network with a Raspberry PI and Python"},"content":{"rendered":"

Sensors are fun!\u00a0<\/em>I wanted to keep an eye on the temperature of one of my home physics projects and realized I needed a thermocouple and a convenient way to read it. This post is about how I got one and wrote a Python program to send the data from a Raspberry PI over the network to my laptop, which plots the results in real time.<\/p>\n

\"Thermocouple<\/a>
Thermocouple in fridge<\/figcaption><\/figure>\n

I bought a K-type thermocouple for several dollars that ranges from -100\u00b0C to 500\u00b0C. The Seebeck effect that makes it work only gives microvolts per degree so I needed a good amplifier for it. And since I wanted to read it on a Raspberry PI (which only has digital inputs), I’d need an analog-to-digital converter (ADC). Conveniently, the MAX31855<\/a> does amplification and ADC and is like $15, so I got one. Sweet. There’s even a Python library<\/a> for it that makes it easy to access. Double-sweet.<\/p>\n

\"The<\/a>
The MAX31855 thermocouple amp and ADC<\/figcaption><\/figure>\n

<\/p>\n

I decided to hook it up to the hardware SPI interface on the PI. This was supposed to be fastest so I figured, why not. On a RPi B+, that’s 3.3V -> Vin, GND -> GND, SCLK(GPIO11)->CLK, CE0 (GPIO 8)->CS, and MISO(GPIO 9)->DO. Easy enough. Then I just uncommented the Hardware SPI section in the Adafruit Python library example and got some readings. Excellent. It actually has a build-in temperature sensor as well so you can get its temperature and the temperature at the end of your thermocouple wire.<\/p>\n

\"first<\/a>
first thermocouple readings<\/figcaption><\/figure>\n

At first I tried getting the Raspberry PI to plot it live. But frankly, it was just too slow to handle the live-plotting plus the encryption and forwarding of the X11 graphics over ssh (I even dumbed down the encryption<\/a> since I was on a local network). Maybe a RPI2 could handle it, but the B+ was too slow. So I got the idea to send the data over the network to my laptop which could spend all the CPU it wanted on animating plots and updating and stuff. I had to learn some stuff about the Python socket module<\/a>, but it was really pretty straightforward. I made a client script that runs on the PI, reading the sensor and transmitting the data. My server script runs on the laptop and receives the data, plotting it live.<\/p>\n

Plotting live data<\/h3>\n
\"Refridgerator<\/a>
Temperature in the refrigerator as the door is opened and then closed<\/figcaption><\/figure>\n

Plotting the live data isn’t too bad with matplotlib, though it was a bit tricky due to the ongoing network communication. First, just get a plot animation going using one of the examples of the FuncAnimation. This decay one is particularly useful<\/a>. Once you have that running and fully understand it, then modify the data_gen method to give you data off the network as it becomes available.<\/p>\n

You’re going to need Threads. The real trick is to use a Queue <\/a>which I learned about in this great presentation on Python concurrency<\/a>. My implementation is still not excellent (it hangs a lot), but it gets the job done. Check out my full code and improve it if you want. It’s hosted on github<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Sensors are fun!\u00a0I wanted to keep an eye on the temperature of one of my home physics projects and realized I needed a thermocouple and a convenient way to read it. This post is about how I got one and wrote a Python program to send the data from a Raspberry PI over the network … Continue reading Data acquisition and live-plotting over the network with a Raspberry PI and Python<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":4,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":""},"categories":[3,69],"tags":[],"class_list":["post-820","post","type-post","status-publish","format-standard","hentry","category-computers","category-electronics-and-physics"],"_links":{"self":[{"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/posts\/820","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/comments?post=820"}],"version-history":[{"count":4,"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/posts\/820\/revisions"}],"predecessor-version":[{"id":911,"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/posts\/820\/revisions\/911"}],"wp:attachment":[{"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/media?parent=820"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/categories?post=820"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/partofthething.com\/thoughts\/wp-json\/wp\/v2\/tags?post=820"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}