Fig 2. Design of an inexpensive control system.
(A) Control design for PID temperature control. The temperature (T) is read by the thermistor at the coverslip, and its difference with respect to the setpoint (Tsetpoint) is used as an input to the PID algorithm. PWM signals are used to modulate the power input to the Peltier module. (B) Circuit design for the temperature-control system. Components are labeled with their estimated itemized price in US dollars. Asterisks indicate items not illustrated in the circuit diagram. The total cost is approximately $106 (S1 Table). LED, light-emitting diode; NTC, negative temperature coefficient; PID, proportional-integral-derivative; PWM, pulse-width-modulation.