Hey all I, I've been fiddling with this the other day and I am trying to use a thermistor with another resistor to make a 2 transistor switch that triggers at the output....take a look at the schematic, and here are my values
VCC = 5V
Thermistor Temperature at room temperature: 5400 ohms
Thermistor temperature while holding it: 4400 ohms
Q1 and Q2 are NPN transistors with ~200 Beta
Basically, I want it so that once i place my fingers on the thermistor and dropped its resistance to 4400 ohms, then it triggers the base of the first transistor and sends voltage to the output of the second transistor (at collector/VCC junction on second transistor)
I calculated my voltage divider as such:
5V * RB/(Resistance of thermistor at room temperature+RB) = .5 V (<.7, so voltage is not high enough to trigger transistor)
Rearranging we have:
5RB = (.5*Rthermistor) + (.5*RB)
5RB = = .5*5400 + .5RB
4.5RB = 2700
RB = 600
So I place a 600 ohm resistor into RB, expecting the voltage to to increase to .7 at the base to trigger it..but nothing happens...what am i doing wrong
VCC = 5V
Thermistor Temperature at room temperature: 5400 ohms
Thermistor temperature while holding it: 4400 ohms
Q1 and Q2 are NPN transistors with ~200 Beta
Basically, I want it so that once i place my fingers on the thermistor and dropped its resistance to 4400 ohms, then it triggers the base of the first transistor and sends voltage to the output of the second transistor (at collector/VCC junction on second transistor)
I calculated my voltage divider as such:
5V * RB/(Resistance of thermistor at room temperature+RB) = .5 V (<.7, so voltage is not high enough to trigger transistor)
Rearranging we have:
5RB = (.5*Rthermistor) + (.5*RB)
5RB = = .5*5400 + .5RB
4.5RB = 2700
RB = 600
So I place a 600 ohm resistor into RB, expecting the voltage to to increase to .7 at the base to trigger it..but nothing happens...what am i doing wrong