Electronics 101

Scott Hamilton

Senior Expert in Emerging Technology

Last week I broke out my electronics kit for a quick project. We decided to start incubating some chicken eggs for spring chicks and noticed that the thermostat on our incubator did not have a temperature readout. The question arose as to how we were going to properly adjust the incubator. We were in the beginning of the winter storm and did not want to drive into town, so we checked the local Dollar General to see if we could get a thermometer; there were none in stock. I had a thermal sensor in my electronics kit so I went to work.

I am fairly certain I have talked about the Arduino micro-controller in the past, but here is a brief review. Arduino is a home, hobbyist level micro-controller, usually priced under twenty dollars and fairly easy to operate. A micro-controller is like a small computer designed for the real-time reading of sensors and controlling of electronics systems. In my particular case, I am only interested in reading a single temperature sensor, but the Arduino is capable of so much more.

The project started with getting the Arduino to read the temperature sensor and tell me the temperature in degrees Fahrenheit. It took a while to find the specifications on the temperature sensor since there were no labels on the sensor, but once I found the specification sheet I had to build the correct circuit to read it properly. The first attempt resulted in reading a temperature of -127 degrees. It was pretty clear that something was not right. As it turns out there are two models of the temperature sensor, one with a built in, pull-up resistor and one without. I had the one without.

A pull-up resistor is a component that goes between the sensor wire and a five volt power supply in order to stabilize the output voltage of a sensor; without the pull-up resistor there will be low voltage because the sensor cannot supply any current to the digital input pin on the Arduino, causing a constant low voltage reading. This explained the -127 degree temperature reading.

I was finally able to read the correct temperature from the sensor and print it to the computer screen on the laptop I was using to program the Arduino, but that leaves the laptop trapped next to the incubator and required for monitoring the temperature. The biggest problem you have when trying to use a micro-controller for a project like this is determining how to read the results from the controller.

A micro-controller does not have a video card or any kind of display and relies entirely on sending and receiving signals. This means that one must design a mechanism to read the results of their sensor as well as a mechanism to read the sensor itself. So begins the second part of the project. I had three light emitting diodes (LEDs), red, yellow, and green; this seemed to be a reasonable way to display the temperature since I was only interested to know if the incubator was too hot, too cold, or in the correct range. I don’t know exactly why, but I decided to use red for too cold, yellow for just right and green for too hot. After writing a few more lines of code and wiring the LEDs to the output pins of the Arduino, I now have a working digital thermometer connected to my incubator.

This is one of the reasons I tend to never throw out broken electronics; everything for this little project came from something that I took apart when it became unrepairable, except for the Arduino which came in a kit from www.arduino.org that is used in training students in electronics. If you are looking for a new hobby I highly recommend picking one up, as you can fix just about anything once you understand micro-controllers. I have a friend that used an Arduino to replace his engine control computer in his classic car when he was unable to buy a replacement. I doubt I ever get that ambitious with micro-controllers, but enjoy tinkering on small projects like the digital thermometer. If you’re interested in the plans, I hope to have them up on my website later this week. You can find the project here.

Until next week, stay safe and learn something new.

Scott Hamilton is a Senior Expert in Emerging Technologies at ATOS and can be reached with questions and comments via email to sh*******@te**********.org or through his website at http://www.techshthepherd.org.