Turtle and Tortoise Newsletter - VET-MAGAZIN.com

Turtle and Tortoise Newsletter, Issue 3Continuous Temperature Measurements in Reptile Enclosures, Using Simple ElectronicEquipment and a Standard Personal ComputerVICTOR J.T. LOEHRStudbook Breeding Programme Homopus, Nipkowplein 24, 3402 EC IJsselstein, Netherlands,Email: loehr@homopus.org, Website: http://www.homopus.orgIncreasing survival pressures on turtles worldwideemphasize the need to develop successful husbandry andbreeding protocols. In conjunction with wildlife managementplans, these may increase survival chances for manyspecies. Although a growing number of species is reportedto propagate successfully in captivity, detailed descriptionsallowing others to reproduce the suitable husbandrypractices, often lack. Sometimes this is caused by restraintsto publish gathered data, but at other times data sets simplyare insufficient.In this article, I describe a relatively easy method tocontinuously monitor the temperature in reptile enclosures,by means of simple electronics and a standard personalcomputer. This offers the possibility to make (andeventually publish) detailed temperature measurements, atreasonable costs and time-investment. While temperatureis important, I realize that it is only one factor involved withsuccessful husbandry and breeding.HardwareThe electronic device consists of a microchip,generating a pulse in a circuit with a capacitor, a resistorand a temperature-dependent resistor (KTY10). Thefrequency of the pulse is the product of the temperaturedependentresistor and the (stable) capacity of thecapacitor, and thus is dependent on the temperature. Whenthe temperature increases, the resistance of thetemperature-dependent resistor will increase, decreasingthe frequency of the pulse. Measurement of the time onepulse takes (and thus temperature) is effected via the serialport of a personal computer (3.86- or 4.86-laptopcomputers are ideal, as they save energy and are usuallyvery silent). A maximum of 4 circuits can be connected to acomputer via one serial plug.The pins of the serial plug are numbered 1-9. Pinnumber 5 (GND) is the ground (-). Pins number 1 (DCD),6 (DSR), 8 (CTS) and 9 (RI) can be used to send signalsfrom four circuits to the computer (+).In order to protect the KTY10-sensor when placed intoa terrarium, it can be covered by a small watertight test tube.SoftwareThe pulse generated by the circuit can be ‘listened to’by the connected computer, using a few lines-program inTurbo Pascal. It records the amount of time (L) needed fora single pulse, using the 1 Mhz clock (8253) in the computer.This program (Program 1) only measures and displaysthe amount of time one pulse takes (for each sensor, everyminute), without translating it to temperature. In order totranslate the time to temperature, the circuitries needcalibration. I have found that this can best be carried outafter complete installation of the hardware (including theKTY10 sensors in the terrariums). Theoretically (andapparently in some cases experimentally), calibration canalso be accomplished by establishing (for each circuit) thefunction between R and L, by temporarily connecting astable 2 kOhm resistor, and after that a stable 1.5 kOhmresistor, instead of the KTY10 resistors. After reading of Lfrom the computer screen, the function between L and Rshould be linear (R = aL + b). Next, R can be translated totemperature, by establishing the resistance of each of theKTY10 resistors at a known temperature range (fridge,freezer, room temperature, et cetera) by means of amultimeter. The function (theoretically also a straight linefor the temperature range usually prevailing in reptileenclosures) found should be included in the computerprogram to display temperature instead of L or R.The components of one circuit are:· Microchip timer TLC555· Stable capacitor 1 uF· Resistor 2kOhm· Temperature dependent resistorKTY10 (± 2 kOhm)· Circuit board· Serial port plug (female)· Power supply 6 V, 200 mAThe circuitry schematic is shown in Fig. 1.Figure 1. Circuitry schematic16