I've built a Schmitt trigger which is connected to a thermistor. Trouble is I want the Schmitt trigger to set off an astable when i heat the thermistor with my fingers but because of the small change in resistance I can't get the astable to be set off without manually turning the variable resistor.
I've tried an LDR and it works fine. Any ideas would be much appreciated. **broken link removed** **broken link removed**
I've built a Schmitt trigger which is connected to a thermistor. Trouble is I want the Schmitt trigger to set off an astable when i heat the thermistor with my fingers but because of the small change in resistance I can't get the astable to be set off without manually turning the variable resistor.
I've tried an LDR and it works fine. Any ideas would be much appreciated.
If you know the on/off temperatures and the resistance of the thermistor at those temperatures, you can calculate the resistor values so there's no need for trimmer resistors, unless you want it to be adjustable of course.
If you use a dual comparator such as the LM393 it's possible to use one comparator as the astable so you don't need to use another IC such as a 555 timer.