Connecting a thermistor to 1.IO5.in
-
HI Im Trying to connect a thermistor to an IO as i have ran out of temp Sensors .
Can any any one help with the wiring of this as im getting poor readings . 89.4 °C at room temp . it warms up when I put heat to it ...
-
@M7460 You haven't said which board you are using but even so, and as far as I know, the io connectors are all digital. A thermistor is an analogue device so you can't read it using a digital io port.
-
@deckingman Im using the - 3HC in this case . Would a Pt1000 work better ?
-
-
@M7460 Ah, OK. I stand corrected. However, getting it to read temperature via a thermistor isn't going to be easy - depends on you level of knowledge. But basically, a thermistor is simply a variable resistor - one which changes resistance depending on temperature. In that respect, a PT1000 is also a thermistor. The usual way to read temperature with a micro-controller is to create a voltage divider circuit. So you have two resistors in series one of which is the thermistor and one is a fixed value. You feed 3.3V into the thermistor, connect the junction between the thermistor and fixed resistor to your input, and connect 0V to the other side of the fixed resistor. So the voltage at the junction between the two resistors will vary depending on the resistance of the thermistor and hence the temperature. It therefore follows that you need to be careful in your selection of the fixed resistor and you'll need to also have some sort of calibration coefficients to convert the measured voltage to temperature. I'm afraid that's as far as my limited knowledge will take me. So someone else will have to help you out with choosing suitable component values and a means of converting the analogue voltage to temperature.
-
@M7460 there is a built-in 27K resistor between the IN pin and the +3.3V pin on all the IO ports. However, to read a standard 100K thermistor you should use an additional lower value resistor connected externally between those two pins. I suggest a value of either 4.7K or 3.3K. Then in the M308 command for that temperature sensor you will need to use the R parameter to tell RRF the effective resistance between the IN pin and +3.3V, which will be the parallel combination of your external resistor and the 27K internal resistor.
