Shop OBEX P1 Docs P2 Docs Learn Events
rctime and lm35?? — Parallax Forums

rctime and lm35??

tercou1tercou1 Posts: 25
edited 2012-01-25 09:05 in BASIC Stamp
is there any schematics that could show me how to connect an lm35 to an rc circuit so that i could connect it to a bs2? do i replace the pot with the temp sensor?? I want the bs2 to alert me if the temp. is approaching 0 degrees celsius. thanks in advance.. anybody with any code regarding this problem would be really appreciated

Comments

  • ercoerco Posts: 20,256
    edited 2012-01-24 16:58
    Neat sensor, but you'll have a hard time RCtiming it directly, its output voltage is too low. It outputs 0 volts at 0 degrees C, then increases 10 mV per degree C. It wouldn't be able to trigger the Stamp's TTL input voltage (~1.4V) until the temp hits 140 degrees C or higher.

    See Tracy Allen's info at http://www.emesystems.com/OL2heat.htm#TF_LM34 and also http://forums.parallax.com/showthread.php?135361-ADC0834-amp-LM34-vs.-Offset&highlight=ds18b20

    You could RCtime a thermistor directly, but you're going to need an op amp or ADC to use that particular sensor.
  • Tracy AllenTracy Allen Posts: 6,662
    edited 2012-01-25 00:20
    Erco is right, the LM35 does not lend itself well to the RCTime method. Is it only the yes/no you are after, above or below freezing, or are you also after quantitative data? T
  • bsnutbsnut Posts: 521
    edited 2012-01-25 00:37
    Are you limited on I/O pins for your application? Why I ask this, is a ADC only needs 3 I/O pins and is able see this sensor small voltage changes.
  • tercou1tercou1 Posts: 25
    edited 2012-01-25 05:02
    hi tracy, it's the yes/no that i'm looking for, I want to be able to tell if the water in a pipe is going to freeze. if it is, then i want the bs2 to alert me via an lcd screen. I suppose i could go the extra mile and have a running temp display on the lcd :) i have been looking at the ds for 0831adc and it seems pretty straight forward.. what do you think?
  • tercou1tercou1 Posts: 25
    edited 2012-01-25 05:27
    Thanks Erco
    erco wrote: »
    Neat sensor, but you'll have a hard time RCtiming it directly, its output voltage is too low. It outputs 0 volts at 0 degrees C, then increases 10 mV per degree C. It wouldn't be able to trigger the Stamp's TTL input voltage (~1.4V) until the temp hits 140 degrees C or higher.

    See Tracy Allen's info at http://www.emesystems.com/OL2heat.htm#TF_LM34 and also http://forums.parallax.com/showthread.php?135361-ADC0834-amp-LM34-vs.-Offset&highlight=ds18b20

    You could RCtime a thermistor directly, but you're going to need an op amp or ADC to use that particular sensor.
  • ercoerco Posts: 20,256
    edited 2012-01-25 09:05
    One last thought just in case your LM35 is loctited in place already. :)

    The voltage output approaching 0 degrees C is very low, but you could run that into a 99-cent comparator (LM339 or equiv), using a trimpot to set a reference voltage. The comparator snaps on when the sensor voltage drops below the reference voltage, and that output can trigger your Stamp or other electronics directly.
Sign In or Register to comment.