This simple circuit can measure temperatures with some accuracy, depending only on how your calibration is done. Based on a thermometer we can have a scale of -40º C to + 125º C.
The sensor is a common silicon diode that can have a long connection to the device, allowing remote temperature measurement.
The device is powered by 4 small cells or 9 V batteries and the drive is only made at the time of reading which greatly extends the life of the power source.
Common components are used and in Figure 1 we have the complete diagram of the apparatus.
In figure 2 we have the assembly using a terminal strip.
Material list:
Q1 - BC548 - NPN general purpose transistor
D1- 1N4148 - common silicon diode
M1- 0-1200 uA - microammeter
S1 – On/Off switch
P1 - 47 k ohms - potentiometer or trimpot
B1-6 or 9 V- batteries or battery
R1- 10 M ohm - resistor, brown, black, blue
R2 - 4k7 - resistor - yellow, violet, red
R3, R4 - 1k ohm - resistors - brown, black, red
Miscellaneous:
Battery holder or battery connector, terminal strip, mounting box, wires, solder, etc.
