Using ANALOGIN (SX/B Compiler) To Read A LM34 Temperature Sensor
alinious
Posts: 51
I am using the ANALOGIN command from the SX/B compiler to read the analog output from a LM34 temperature sensor. When I warm the temperature sensor, I see the temperature change from approximately 80 degrees Fahrenheit to 87 degrees Fahrenheit on my digital multimeter. If I add the temperature sensor to my circuit, I get an output (being sent via RS-232 to Basic Stamp Debug Terminal) of 109 to 111 by using the ANALOGIN command, but when I warm the sensor, it continues to output 109 to 111 even though the sensor has increased its voltage output.
I initially started by connecting a potentiometer to the circuit and recorded output values of 0 to 239 in order to test my circuit and program. I believe an output of 0 to 239 when using a potentiometer is normal due to the high input impedance of the circuit. Therefore, is it possible that the input impedance to the circuit is not allowing me to see a change in the output (from the SX) when I warm the temperature sensor? What could I change so as to be able to see the output from the SX change as the analog value of the temperature sensor changes?
I have included the schematic as to how the temperature sensor is connected to the SX along with the source code I am using.
Thank-you,
Alan
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Post Edited (alinious) : 12/2/2006 9:29:59 PM GMT
I initially started by connecting a potentiometer to the circuit and recorded output values of 0 to 239 in order to test my circuit and program. I believe an output of 0 to 239 when using a potentiometer is normal due to the high input impedance of the circuit. Therefore, is it possible that the input impedance to the circuit is not allowing me to see a change in the output (from the SX) when I warm the temperature sensor? What could I change so as to be able to see the output from the SX change as the analog value of the temperature sensor changes?
I have included the schematic as to how the temperature sensor is connected to the SX along with the source code I am using.
Thank-you,
Alan
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"I learn when I succeed, but I learn more when I fail."
Post Edited (alinious) : 12/2/2006 9:29:59 PM GMT
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Comments
If the meter shows the voltage going up but the ANALOGIN reading is not, (you do have the both connect at the same time ?) then try using a different value cap (I suspect you need a smaller value, but try a larger one too). Also try increasing the "prime" value from 1 to 4 or 5 and see if that makes a difference.
What can happen is if you have too small of a cap, the voltage will not become steady and will just keep jumping up and down as the feedback changes. If you have too large of a cap, the voltage takes too long to become steady (a larger prime value helps here).
I think original circuit was for 4MHz, you are using 20Mhz so the original circuit should work if you make prime = 5 (because you are 5 times faster).
Let us know if anything helps...
Bean.
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