A Pc-based thermocycler for polymerase chain reactions is described. I
t uses electric heaters and 4 degrees C water for heating and cooling
respectively. The temperature control is built around the easily acces
sible parallel printer adaptor of an IBM-compatible pc. An Ic temperat
ure transducer LM335 is used for sensing the temperature. Pulse width
modulation of the Ac mains is used to control the energy output to the
heaters. The cost of the set-up, excluding a pc and a chiller, is aro
und US$100. The thermocycler was tested in amplifying DNA in actual la
boratory situations.