Robert Onkenhout
This short program will use voltage measurements on the base and collector of a transistor and resistor values entered to calculate the current gain. Of course different value resistors will result in different beta values. I tried to use the smallest collector resistor possible without causing the collector voltage to rise too much. I used the USB (5V) output for the collector resistor, so make sure the collector voltage doesn't rise over 3.3V or I think bad things will happen.
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main.cpp
00001 #include "mbed.h" 00002 00003 AnalogIn base_voltage(p15); 00004 AnalogIn coll_voltage(p16); 00005 00006 int base_resistor, coll_resistor; 00007 float base_current, adj_base_voltage; 00008 float coll_current, adj_coll_voltage, beta; 00009 00010 int main() { 00011 00012 printf ("Please enter a base resistor value\n"); 00013 scanf ("%i", &base_resistor); 00014 00015 printf("Please enter a collector resistor value\n"); 00016 scanf ("%i", &coll_resistor); 00017 00018 //calculate base current 00019 adj_base_voltage = (1 - base_voltage) * 3.3; //voltage across base resistor 00020 base_current = adj_base_voltage/base_resistor; 00021 00022 //calculate collector current 00023 adj_coll_voltage = (1.515 - coll_voltage) * 3.3; //1.515 is 5V as 1 is 3.3V 00024 coll_current = adj_coll_voltage/coll_resistor; 00025 00026 //calculate current gain 00027 beta = coll_current / base_current; 00028 printf ("Transistor beta is %f\n", beta); 00029 printf ("The voltage across Rb is %f\n", adj_base_voltage); 00030 printf ("The voltage across Rc is %f\n", adj_coll_voltage); 00031 00032 } 00033 00034 00035 00036 00037 00038 00039 00040 00041
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