Arduino: Cheap Sensors Cheap Results…

Ramen Junkie August 20, 2015 1Comment

I mentioned last post I had ordered some cheap Temperature and Humidity Sensors for my Arduino boards.  Well they came in, and so I got to do some nice experimenting with code to test them out.  I already had a bit of code from the DHT Test Sketch (Arduino programs are called Sketches) that would poll one sensor and display the results over serial.  Sort of the ultimate goal here is potentially running several fo these sensors around the house and polling them to gather temperature data and store it in a data base that can be accessed via the web.

The first step is getting a Sketch that would poll each sensor and output the result over the serial monitor, preferably with labels.  I started out cutting and pasting the original single sensor code repeatedly and altering the pin before realizing a loop would be way more efficient for this task.  After some fiddling I came up with the following Sketch which polls pins 2-7 sequentially in 2 second intervals and outputs the data to the serial monitor.  This code requires the basic DHT includes from the DHT library.

//
//    FILE: Six Sensor Temp/Humidity Probe.ino
//  AUTHOR: Josh Miller
// VERSION: 0.1.00
// PURPOSE: DHT library based sketch for multiple Temp/Hum probes on Arduino
//     URL: http://www.joshmiller.net
//
// Released to the public domain
//

#include “dht.h”

dht DHT;

void setup()
{
Serial.begin(115200);
Serial.println(“Multi Sensor Temp/Humidity Readings”);
Serial.println(“Version 1.0”);
Serial.println(“Modified DHT Library Version”);
Serial.println(“By Josh Miller, josh@lameazoid.com”);
Serial.println();
}

void loop()
{
int i=1;

while (i<7)
{
// READ DATA

int chk = DHT.read11(i+1);
switch (chk)
{
case DHTLIB_OK:
Serial.print(“\t”);
break;
case DHTLIB_ERROR_CHECKSUM:
Serial.print(“Checksum error,\t”);
break;
case DHTLIB_ERROR_TIMEOUT:
Serial.print(“Time out error,\t”);
break;
default:
Serial.print(“Unknown error,\t”);
break;
}
// DISPLAY DATA
Serial.print(“Probe “);
Serial.print(i);
Serial.print(” : Humidity is: “);
Serial.print(DHT.humidity, 1);
Serial.print(“, Temperature is: “);
Serial.print(DHT.temperature, 1);
Serial.println(” C “);

i++;
delay(2000);
}

}
//
// END OF FILE
//

I don’t have my Network Shields yet so I can’t play around with getting these numbers to dump into an SQL database (probably one running on my NAS) just yet.  This basic proof of concept though is great since it allowed me to learn some code and test the basic functionality of the sensors.  This code can be modified for any number of sensors by changing the “while (i<7)” line to “while (i<# of Pins/sensors Used)”.

Wiring up the bread board was also a bit of a tricky task, mostly because of the sheer number of connections being made.  Each sensor gets a +Voltage and Ground connection off the bus bar and a wire from the senor.  The new cheap sensors use a different pin out from my “official” expensive senor, not really a problem, but something to look out for.

After wiring everything up, I could plug the Arduino into my laptop and open the serial monitor on the appropriate baud rate and record the results.  The results are actually a bit worrying but further testing will be needed to verify the integrity of the results…

Multi Sensor Temp/Humidity Readings
Version 1.0
Modified DHT Library Version
By Josh Miller, josh@lameazoid.com

Probe 1 : Humidity is: 58.0, Temperature is: 25.0 C
Probe 2 : Humidity is: 46.0, Temperature is: 27.0 C
Probe 3 : Humidity is: 41.0, Temperature is: 29.0 C
Probe 4 : Humidity is: 40.0, Temperature is: 26.0 C
Probe 5 : Humidity is: 35.0, Temperature is: 30.0 C
Probe 6 : Humidity is: 36.0, Temperature is: 32.0 C
Probe 1 : Humidity is: 58.0, Temperature is: 25.0 C
Probe 2 : Humidity is: 46.0, Temperature is: 27.0 C
Probe 3 : Humidity is: 41.0, Temperature is: 29.0 C
Probe 4 : Humidity is: 40.0, Temperature is: 26.0 C
Probe 5 : Humidity is: 35.0, Temperature is: 30.0 C
Probe 6 : Humidity is: 36.0, Temperature is: 31.0 C
Probe 1 : Humidity is: 58.0, Temperature is: 25.0 C
Probe 2 : Humidity is: 46.0, Temperature is: 27.0 C
Probe 3 : Humidity is: 42.0, Temperature is: 29.0 C
Probe 4 : Humidity is: 40.0, Temperature is: 26.0 C
Probe 5 : Humidity is: 36.0, Temperature is: 30.0 C
Probe 6 : Humidity is: 37.0, Temperature is: 30.0 C
Probe 1 : Humidity is: 58.0, Temperature is: 25.0 C
Probe 2 : Humidity is: 46.0, Temperature is: 27.0 C
Probe 3 : Humidity is: 42.0, Temperature is: 29.0 C
Probe 4 : Humidity is: 40.0, Temperature is: 26.0 C
Probe 5 : Humidity is: 36.0, Temperature is: 29.0 C
Probe 6 : Humidity is: 37.0, Temperature is: 30.0 C
Probe 1 : Humidity is: 58.0, Temperature is: 25.0 C
Probe 2 : Humidity is: 46.0, Temperature is: 27.0 C
Probe 3 : Humidity is: 43.0, Temperature is: 28.0 C
Probe 4 : Humidity is: 40.0, Temperature is: 26.0 C
Probe 5 : Humidity is: 36.0, Temperature is: 29.0 C
Probe 6 : Humidity is: 38.0, Temperature is: 30.0 C

Probe 1 is the official sensor, the one that cost me $10, the other 5 are cheap probes, they cost me like $9 total.  I have to assume that Probe 1 is pretty accurate and probably has gone through some quality testing before being sold.  The other 5, for all I know, are rejects that were swept off of some floor in China by the janitor.  The point is, all of the readings of the cheap sensors are pretty off from each other, especially the humidity.  This may actually be the case if these sensors were in separate rooms or even any distance from each other, however, these senzors are all within a few centimeters of each other on the same bread board.

There may be a few things happening here causing this discrepancy, and I only say this because they are at the very least consistent with themselves.

One, it’s possible, that there isn’t enough juice to run all of the sensors at once.  If they are being under powered, I would likely get bad readings.  I can easily test this by running each sensor independently with the old single probe Sketch.

Two, it’s possible that while no accurate to each other, they are accurate to themselves.  I don’t really know what these numbers actually mean, I am assuming % Humidity and Degrees C.  It may be some sort of internal scale factor and I simple need to adapt the program to return scaled results.  The issue with this will be that each probe is polled in a loop, so there isn’t really an easy way to apply a different scale factor to each sensor individually.

Whatever the case, the Temperature is at least semi precise, which is what I care more about anyway.  I’ll probably continue with the project with the idea that if I really want accurate results I could eventually invest in better sensors.  The next step on the software end will be to add network functionality to record the data.  On the hardware end I plan to use some CAT5 wire to allow the probes to be positioned in various places beyond just the Bread Board.

OSEPP Arduino Starter Kit

Ramen Junkie August 18, 2015 2Comments

So, a month or so ago, while traveling for work, I was bored in the hotel room and found out there was a Fry’s Electronics around the corner from the hotel. I decided to pop in and look around and see if I could find anything interesting. I also wanted to see how much Raspberry Pi 2B boards were there (and if they were comparable to Amazon.) They had a couple of Pis, a large selection of basic electronic components and a pretty decent selection of Arduino shields and parts.

I’d been looking into getting an Arduino for a while and decided what the hell. There may have been single packed Arduino boards but I really couldn’t tell from the cards which was the base board an which was just an add on shield. I ended up with the OSEPP Arduino Basic Starter Kit.  Honestly, since I hadn’t ever used an Arduino, I didn’t own an Arduino, and I had some basic but not super amazing electronics skills, this really was the best choice.

The kid includes a lot of nice basic parts as well as a guide book to get you started using these basic parts.  The box itself promotes the major projects of “Volt Meter”, “LED Game” and “Electronic Buzzer”.  It also runs through the basics of lighting up some LEDs.  The tutorials are decent though I wish there was a little more on the basics of how to work the bread board and the little wires.  It’s not hard to figure out, but it also isn’t super self explanatory if you didn’t have any experience with electronics at all.  the Volt meter tutorial is less exciting than hoped and the Buzzer just runs up the music scales but it could be modified to play a tune using the little piezo buzzer.

The LED game is neat, but simple.  You make the lights flash in sequence and you must press the button when the appropriate light is flashing, which causes the lights to flash faster.  There is also a 7 segment LED in the kid, which you make count down from 9 to 0.  This actually has a lot of fun potential and I have some ideas for it but I need to figure out how to light up both numbers to display a number (such as say, a temperature).

After exhausting the fun of the starter manual, on my next trip to the area, I bought a temperature and humidity sensor and wired it up.  This was a bit trickier since it required figuring out how to find and download the necessary libraries and modifying the code a bit to get it to read properly.  In the end, I managed to get things working though, which was kind of great since the AC in my hotel room didn’t have a digital read out, so I could know exactly how cold it was and why I was either freezing or sweating.

So, fast forward a bit more again, I’ve got some fun ambitions going and the idea of playing with several Arduino projects.  Unfortunately, while cheap, Arduino boards can add up to expensive.  Unless you buy cheap Chinese knockoffs for $3 apiece off of AliExpress.  I also have some cheap Network boards and temperature sensors coming.  Five boards total, five sensors and two network shields, for around $35, really isn’t too bad of a deal if it all works.

And thus, I have a ton of Arduino boards to play with now.