The Electronic Cricket

By Thomas O'Neill
o'neill@csvrgs.k12.va.us
C. Shenandoah Valley R. Governor's School

Objectives:

1. The student will demonstrate knowledge of thermistors and the effect of heat on resistance by plotting the chirps (or flashes) versus temperature and determining the linear relationship.
   
2. The student will demonstrate knowledge of temperature by using the electronic cricket to measure the temperature of hot, warm, cool and cold water .
   
3. Supplemental (if students construct their own device)
4. The student will demonstrate knowledge of circuit diagrams by constructing an electronic device.
   

Virginia Standards of Learning: (revised 1988)

Third grade: 3.3, 3.4, 3.5
Fourth grade: 4.4, 4.7
Sixth grade: 6.2
Eighth grade: 8.1, 8.4, 8.9, 8.11
Twelfth grade: 12.1, 12.3, 12.11, 12.16, 12.17

Scope, Sequence and Coordination of Secondary School Science
from The Content Core , Vol. 1 (1993). The National Science Teachers Association. Washington, DC.

Grades 6-8
Energy - thermal (pg. 101 and pg. 105)
Electricity and magnetism - electric circuits (pg. 102 and pg. 107-9)
Grades 9-10
Energy -transformations (pg. 101 and pg. 106)
Electricity and magnetism - electric circuits (pg. 102 and pg. 107-9)
Grades 11-12
Electric circuits (parallel) (pg. 102 and pg. 109)

Project 2061
from Benchmarks for Science Literacy (1993) American Association for the Advancement of Science. Washington, DC.
The Nature of Science: The Scientific World View (1A pp. 5-7)

Kindergarten through Grade 2
Grades 3 through 5

The Nature of Science: Scientific Inquiry (1B pp. 10-13)

Kindergarten through Grade 2
Grades 3 through 5
Grades 6 through 8
Grades 9 through 12

The Physical Setting: Forces of Nature (4G pp. 94-97)

Kindergarten through Grade 2
Grades 3 through 5
Grades 6 through 8
Grades 9 through 12

Equipment and materials:

• thermistor (Radio Shack 271 -110 $1.99)
• 9 volt battery
• 10 ½ resistor (Radio Shack 271 -1301 $0.10)
• 2.2 K½ resistor (Radio Shack 271 -1325 $0.10)
• 100 µF capacitor (Radio Shack 271 -1016 $0.99)
• 555 Dual Timer IC (Radio Shack 276-1723 $1.19)
  with 8 pin IC Socket (Radio Shack 276 -1995 $0.30)
• 8 ½ Speaker or LED (Radio Shack 276 -041 $0.50)
• Wire (solid 18 or 20 or 22 gauge)
• Dual IC Board (Radio Shack 276 -158 $1.69) if permanent
  or small breadboard (Radio Shack 276 -175 $7.99) if temporary
  Soldering iron if permanent
  

Reference:

Mims, Forrest M. Engineer’s Mini-Notebook Science Projects (Radio Shack 276 -5018) 1990 Radio Shack pg. 45

Construction of electronic cricket:

The circuit diagram is shown below with the corresponding pins of the 555 IC chip labeled. The 555 IC chip will have a diagram on the back of the package which specifically identifies the number of each pin. Typically, there will be a small circle or dot besides the #1 pin. The #1 through #4 pins are on one side of the chip while #5 through #8 are on the opposite side. The 8½ speaker which is shown in the circuit diagram can be replaced by the LED. The longer leg of the LED should be connected to the 10 ½ resistor while the shorter leg is connected to the #3 pin of the 555 IC chip.

The thermistor should have extra long leads so that it can act as a probe. The battery should be connect so that the + side goes the point marked +9 V and the - side goes to ground. If the project is to be permanent, then the use of an IC socket is advised as soldering leads directly to the pins can damage the IC chip. The project can be successfully set up on a breadboard.

Once the project is wired and tested, it should be calibrated by counting the flashed (or clicks) for one minute at various temperatures. One method is to wrap the thermistor probe (and its leads) in plastic wrap and put it in a cup of water with a regular thermometer. The experimenter should wait at least two minutes for thermistor to come to equilibrium before counting the number of flashes. A simpler method is to an outdoor thermometer with the apparatus left outside for some period of time. Taking readings over the period of one day will usually give a 20-30° range on the Fahrenheit scale. A typical calibration graph is shown below:

Calibration graph

Suggested experiments:

1. The students should first calibrate the cricket over some appropriate temperature range.
2. The students should take equal volumes of hot and cold water in Styrofoam cups. They should rapidly determine the flash count for each cup and then combine the hot and cold water into one cup and count the flash rate after stirring briefly. The simplest form of this experiment is to have a cup one-third full of hot water and another cup one-third full of cold water. Determine the count for each cup ending in the cold water cup. Add the hot water to the cold water cup and stir with a plastic coffee stirrer for fifteen seconds.
3. Then count the flash rate for the new volume of water. The new count should be the average of the hod and cold counts.
4. The experiment above can be repeated for different volumes of hot and cold water (suggestion: use simple ratios like 2 cold to 1 hot). The students can develop a simple model for calorimetry.
   The cricket can be used to monitor outside temperatures on a daily basis as part of a weather program.
5. Student experimenters should also examine the effect of changing the 2.2 K½ resistor to some other value (such as 1 K½ or 4.7K½) on the flash rate of the LED. The students should also change the capacitor (try 47 µF or 220 µF).
   

Back to the Teaching Ideas Page

Back to the Virginia Instructors of Physics Home Page.

This page was posted on 2/26/99