Mosquito control
An exclusive interview with a test engineer
Senior Technical Editor Martin Rowe -- Test & Measurement World, 9/1/2008
Abel Raynus is an electrical engineer at Armatron International’s Flowtron Outdoor Products Division. Once known as Automatic Radio, a manufacturer of car radios, Armatron International now manufactures lawn and garden products through its Flowtron division. Raynus designed the electronics and the testers used in production of the company’s electronically controlled mosquito-control products. Senior technical editor Martin Rowe met with Raynus at his office in Malden, MA.
Q: What kind of electronics are in a mosquito killer?
A: The mosquito killer uses a microcontroller to control an exothermic reaction that produces carbon dioxide from propane gas. The microcontroller controls a heater and it also handles the user interface, which contains buttons for setting the amount of time that the mosquito killer is on. LEDs tell the user when the product is on and working.
Q: How does the microcontroller control the exothermic reaction?
A: When you first start the mosquito killer, the heating element is cold. The controller turns on the heater while monitoring the internal temperature. As temperature rises, the propane gas produces CO2, which simulates human breathing that attracts mosquitoes. As internal temperature rises, the microcontroller adjusts the gas flow, which controls temperature.
Q: How does the unit monitor temperature?
A: Thermocouples in the unit measure internal temperature, and thermistors monitor outside temperature. A photocell senses light that the microcontroller uses to turn the unit off during daylight hours. The microcontroller has built-in analog-to-digital converters that measure the temperature and light levels.
Q: How do you program the microcontroller?
A: I program in assembly language. It’s much more efficient than writing code in C. By writing the code in assembly language, I was able to fit the control algorithm into 4 kbytes of program memory.
Q: What kind of tester did you design?
A: I designed a test fixture to verify that the controller boards function properly. The fixture contains spring-contact pins that connect to a microcontroller-based board in the tester. The tester’s board measures voltages on the board under test. A go/no-go LED tells the operator if the board under test has passed all tests. If it hasn’t, then other LEDs indicate which tests failed. From those LEDs, we get enough information to troubleshoot and repair the board.
Q: What tools do you use for design and test of new microcontroller boards?
A: I have all the usual tools such as oscilloscopes, signal generators, and multimeters. I also use electronic-circuit-design and printed-circuit-board layout software.
Q: Do you have to justify the purchase of electronic parts and tools?
A: Not if they are required in the development of new designs that have been approved and authorized by management.
