Posted 11 January 2017
I’ve had at least one 3D printer in my home laboratory for well over 2 years now, and having the ability to print up arbitrary 3D shapes has been a complete creative game-changer for me. Now when I have an idea about something I want to build or try, I don’t have to spend days in my shop trying to fabricate something out of wood or sheet metal – I can design it in TinkerCad and print it on my 3D printer. Moreover (and this is where it gets really cool!), I don’t have to get it right the first time – I can make an unlimited number of versions of the idea, improving and/or changing it as I go. Each iteration takes a few hours at most, and costs just a few pennies in terms of power and filament usage – what a deal!
Anyway, I have accumulated a number of rolls of different filaments, all of which degrade in greater or lesser degree over time due to moisture absorption (hygroscopic tendency). I
haven’t worried too much about this up to now, mostly because my lab is in an air-conditioned house in the midwest, where humidity levels are low to begin with. However, I recently started seeing some printing problems that led me to believe that I may need to address this issue. In my typically over-the-top fashion, I decided that if I was going to work this problem, I needed a way to monitor the actual temperature & humidity in whatever arrangement I tried.
First, as usual, I did some web research, and found a solution implemented by the folks at the Taulman specialty 3D filament fabrication house. Their solution was a 5-gallon plastic bucket with some air-holes, a 40-60 Watt lightbulb, and a wooden dowel. This allowed them to combine a dehumidifier with a filament delivery system. I fabricated one of these myself, but wasn’t particularly happy with the results. While it worked fine, there was only room for two rolls of filament at a time, while I have literally dozens of rolls of different filaments. In addition, I had no way of knowing what the actual temperature and relative humidity were inside the bucket – for all I knew, it could be doing nothing but wasting 40 watts of electricity!
So, I decided to combine my pile of 3D filaments, my 3D printing super-powers, and my Electrical Engineering Mad Scientist background to come up with a better solution to the filament drying problem.
Temperature/Humidity Sensors
The DIY/Robotics/Hobbyist market has spawned all sorts of new capabilities, so I was not at all surprised to find that temperature/humidity sensors were cheap and readily available. I started with the cheaper DHT11 (I figured I would kill at least one sensor before getting it right), but later moved on to the DH22. The DH11 humidity measurement range stops at 20% on the low end, and since I am trying to obtain humidities at or below that value, I decided to blow out my sensor budget from around $5/unit to around $10 – a real budget-breaker (not)!
DHT11 Temp/Humidity sensor, shown here from Adafruit. 20-80% RH range with +/- 5% accuracy
DHT22 Temp/Humidity sensor, shown here from Adafruit. O-100% RH range with +/- 2.5% accuracy
Arduino Uno Controller
In order to effectively use the RH sensors, I needed a controller of some sort. Happily for me, there was already a DHT11/22 library available for the wonderful Arduino line of controllers, and I happened to have several Arduino Uno’s lying around waiting for something to do. Connecting up the sensor, and getting a program working was a matter of just a few lines, most of which had already been written in the form of an example program
8-Character LCD Display
When I first started this project, I thought it would be adequate to simply connect the arduino to my PC to readout the data. This worked, but turned out to be cumbersome; I had to have a physical connection to the controller, which was located inside the dehumidifier bin. Later I tried a Wixel connection, which also worked, but still meant that I had to bring up a serial port app on my PC to find out what my dehumidifier bin was doing. What I really wanted was a completely self-contained system, so I could simply look at some sort of display on or in the bin and tell whether or not things were working. After doing a bit more web research, I found the Sparkfun ‘Basic 8-character LCD display’ for all of $4.95 (plus shipping). In addition, this display (plus a number of others with different character arrangements) were easily integrated into an Arduino program by means of the built-in ‘LiquidCrystal’ Library – nice!!
So now I had all the pieces – a sensor (DHT22), a controller (Arduino Uno), and a display for readout (Sparkfun 8×2 LCD). Now what I needed was a nice, custom-made box to house them, and just coincidentally I had 3D printer and LOTS of filament hanging around just waiting for a project! ;-). As usual, I went through several iterations (you would think that it would be pretty hard to screw up a simple box design, but I’m highly creative when it comes to finding new ways!). When I was finished, I had a nice little box with enough room for everything, a recessed lid, and appropriately placed holes for the power connector, the USB connector, and the sensor cable, as shown below
To complete the project, all I had to do was drill some holes in a handy transparent storage bin, load it up with filament rolls and a 40-watt trouble light, and set the sensor box inside where the readout would be visible from the outside. The whole thing was installed on a shelf over my workbench, so I can simply walk up to the bin and see the readout from eye level – neat!
Now all I have to do is wait a day or so to see where the system stabilizes, and make whatever airflow adjustments are necessary. For anyone who cares, I have included below the Arduino sketch for the project.
15 January 2017 Update: After 24 hours, the system stabilized to around 85 º F (29.4C) and about 26%, which I thought wasn’t enough better than room environment to make a difference, so I closed off about half of the air-holes. After another 24 hours or so, the system re-stabilized at about 90 º F (32.2C) and 21% humidity – much nicer!
17 February 2017 Cleanup: Here is the code to display temperature & humidity on the LCD display, and also make the data available at the serial port.
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// DHT Temperature & Humidity Sensor // DHT Temperature & Humidity Sensor // Unified Sensor Library Example // Written by Tony DiCola for Adafruit Industries // Released under an MIT license. // Depends on the following Arduino libraries: // - Adafruit Unified Sensor Library: https://github.com/adafruit/Adafruit_Sensor // - DHT Sensor Library: https://github.com/adafruit/DHT-sensor-library #include<LiquidCrystal.h> // include the LCD library code: #include<Adafruit_Sensor.h> #include<DHT.h> #include<DHT_U.h> // initialize the library with the numbers of the interface pins //01/07/17 gfp: my setup is: //LCD pin name RS EN DB4 DB5 DB6 DB7 //Arduino pin # 7 6 5 4 3 2 LiquidCrystal lcd(7, 6, 5, 4, 3, 2); #define DHTPIN 8 // Pin which is connected to the DHT sensor. // Uncomment the type of sensor in use: //#define DHTTYPE DHT11 // DHT 11 #define DHTTYPE DHT22 // DHT 22 (AM2302) //#define DHTTYPE DHT21 // DHT 21 (AM2301) // See guide for details on sensor wiring and usage: // https://learn.adafruit.com/dht/overview DHT_Unified dht(DHTPIN, DHTTYPE); uint32_t delayMS; double tempF = 0; //holds temperature returned from DHT22 double RelHumPct = 0; //holds relative humidity returned from DHT22 void setup() { Serial.begin(115200); // Initialize Temp/Humidity sensor. dht.begin(); Serial.println("DHTxx Unified Sensor Example"); // Print temperature sensor details. sensor_t sensor; dht.temperature().getSensor(&sensor); Serial.println("------------------------------------"); Serial.println("Temperature"); Serial.print("Sensor: "); Serial.println(sensor.name); Serial.print("Driver Ver: "); Serial.println(sensor.version); Serial.print("Unique ID: "); Serial.println(sensor.sensor_id); Serial.print("Max Value: "); Serial.print(sensor.max_value); Serial.println(" *C"); Serial.print("Min Value: "); Serial.print(sensor.min_value); Serial.println(" *C"); Serial.print("Resolution: "); Serial.print(sensor.resolution); Serial.println(" *C"); Serial.println("------------------------------------"); // Print humidity sensor details. dht.humidity().getSensor(&sensor); Serial.println("------------------------------------"); Serial.println("Humidity"); Serial.print("Sensor: "); Serial.println(sensor.name); Serial.print("Driver Ver: "); Serial.println(sensor.version); Serial.print("Unique ID: "); Serial.println(sensor.sensor_id); Serial.print("Max Value: "); Serial.print(sensor.max_value); Serial.println("%"); Serial.print("Min Value: "); Serial.print(sensor.min_value); Serial.println("%"); Serial.print("Resolution: "); Serial.print(sensor.resolution); Serial.println("%"); Serial.println("------------------------------------"); // Set delay between sensor readings based on sensor details. delayMS = sensor.min_delay / 1000; // set up the LCD's number of columns and rows: //lcd.begin(16, 2); lcd.begin(8, 2); // Print a message to the LCD. //lcd.print("hello, world!"); //String str = "Temp: "; //str += "43"; //lcd.print(str); } void loop() { // Delay between measurements. delay(delayMS); // Get temperature event and print its value. sensors_event_t event; dht.temperature().getEvent(&event); if (isnan(event.temperature)) { Serial.println("Error reading temperature!"); } else //good data { //12/07/16 temp is in C - convert to F tempF = event.temperature * (9.0 / 5.0) + 32; Serial.print("Temp/Humidity: "); Serial.print(tempF); Serial.print(" F\t"); } // Get humidity event and print its value. dht.humidity().getEvent(&event); if (isnan(event.relative_humidity)) { Serial.println("Error reading humidity!"); } else //good data { RelHumPct = event.relative_humidity; //Serial.print(event.relative_humidity); Serial.print(RelHumPct); Serial.println(" %"); } //// set the LCD cursor to column 0, line 1 //// (note: line 1 is the second row, since counting begins with 0): //lcd.setCursor(0, 1); //// print the number of seconds since reset: //lcd.print(millis() / 1000); //set the LCD cursor to column 0, line 0 (1st line) lcd.setCursor(0, 0); String str = "T: "; str += String(tempF,1); lcd.print(str); //set the LCD cursor to column 0, line 1 (2nd line) lcd.setCursor(0, 1); str = "RH:"; str += String(RelHumPct,0); lcd.print(str); } |
Frank