Post by thread:[PIC]: Relative Humidity Sensor

Does anyone have a favorite PIC compatible humidity sensor? I was looking for something inexpensive, and low accuracy (5 or 10%). I want to replace the mechanical humidistat on my humidifier with a PIC based solution that I can connect into my home automation system. Thanks... Allan Dobler -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Check http://www.honeywell.com They are not so inexpensive but have a conditioned output you can use with a built in AD PIC. Marcelo Y. {Quote hidden}> Does anyone have a favorite PIC compatible humidity sensor? I was > looking for something inexpensive, and low accuracy (5 or 10%). I want > to replace the mechanical humidistat on my humidifier with a PIC based > solution that I can connect into my home automation system. > Thanks... > Allan Dobler > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Another guy suggested honeywell sensors. They are great, but at $500 to $1000 a crack, and 1% accuracy, you probably can't afford one. Here's how you do a cheap and dirty humidity sensor. The most basic humidity sensor is a dry bulb/wet bulb sensor. It senses the dry bulb temperarature with a standard temperature sensor, then also senses the temperature insite a wetted cloth sack (the wet bulb). A wet cotton sock might work OK for this. I built a controller for a $30,000 environmental chamber using precision wet and dry bulb thermocouples. This method can be very accurate and precise, it is not just for hackers. Now there is a complex formula relating wet and dry bulb to humidity, but you don't care about it. All you need is a lookup table for a few setpoints. You _might_ even get away with just measuring wet bulb temperature if the air you are measuring is relatively constant dry bulb temperature. I've got references (ASHRAE handbook) that I can give you if you want to look into this method further. The last problem is keeping the wet bulb wet. You are using a humidifier, so you already have a source of water handy. Shouldn't be too hard to hack together. You also have to keep air moving over the wet bulb, to evaporate water. This also shouldn't be too hard in a heating duct. Be careful about corrosion - use plastic parts in contact with the water. Maybe an epoxy encapsulated Dallas temperature sensor chip would work nicely. I can send you a photo of my wet/dry bulb setup offlist if you are interested. -- Lawrence Lile {Original Message removed}

Allan, check out General Eastern's G-CAP line: General Eastern: http://www.geinet.com/ - Tom At 10:53 PM 12/28/00 -0700, Allan wrote: >Does anyone have a favorite PIC compatible humidity sensor? I was >looking for something inexpensive, and low accuracy (5 or 10%). I want >to replace the mechanical humidistat on my humidifier with a PIC based >solution that I can connect into my home automation system. >Thanks... >Allan Dobler ------------------------------------------------------------------------ Tom Handley New Age Communications Since '75 before "New Age" and no one around here is waiting for UFOs ;-) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Thanks for the links guys, that helps out a lot Allan > > > Does anyone have a favorite PIC compatible humidity sensor? I was > > looking for something inexpensive, and low accuracy (5 or 10%). I want > > to replace the mechanical humidistat on my humidifier with a PIC based > > solution that I can connect into my home automation system. > > Thanks... > > Allan Dobler -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Fri, 29 Dec 2000, Tom Handley wrote: > Allan, check out General Eastern's G-CAP line: > > General Eastern: http://www.geinet.com/ Which look really nice, and if anyone has a way to get just a couple at a reasonable price I'm interested. I have yet to find a similar RH sensor that I can obtain one or two of for a few bucks. Dale --- The most exciting phrase to hear in science, the one that heralds new discoveries, is not "Eureka!" (I found it!) but "That's funny ..." -- Isaac Asimov -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 10:00 PM 12/30/00 -0600, you wrote: >On Fri, 29 Dec 2000, Tom Handley wrote: > > > Allan, check out General Eastern's G-CAP line: > > > > General Eastern: http://www.geinet.com/ > >Which look really nice, and if anyone has a way to get just a couple at a >reasonable price I'm interested. I have yet to find a similar RH sensor >that I can obtain one or two of for a few bucks. I bought an evaluation kit from them with 5 sensors. They'll probably send you a free sensor or two. ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: spam_OUTralTakeThisOuTlcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================ -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hi Dale, I have been scouring the net for a week, and I can't find anyone that will sell one or two RH sensors either. They are usually 1000 lot minimum, or they cost $100 ea. I have seen $25 RH/temp battery powered desktop units that display to a 7 segment LCD. I may have to cannibalize the sensor out of those. That seems like a waste though. Allan Dale Botkin wrote: {Quote hidden}> > On Fri, 29 Dec 2000, Tom Handley wrote: > > > Allan, check out General Eastern's G-CAP line: > > > > General Eastern: http://www.geinet.com/ > > Which look really nice, and if anyone has a way to get just a couple at a > reasonable price I'm interested. I have yet to find a similar RH sensor > that I can obtain one or two of for a few bucks. > > Dale > --- > The most exciting phrase to hear in science, the one that heralds new > discoveries, is not "Eureka!" (I found it!) but "That's funny ..." > -- Isaac Asimov > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Sat, 30 Dec 2000, Allan wrote: > Hi Dale, > I have been scouring the net for a week, and I can't find anyone that > will sell one or two RH sensors either. They are usually 1000 lot > minimum, or they cost $100 ea. I have seen $25 RH/temp battery powered > desktop units that display to a 7 segment LCD. I may have to > cannibalize the sensor out of those. That seems like a waste though. I know, my $29 Radio Shack thermometer/hygrometer has a sensor in it that could not possibly have cost more than $.50 in any sort of quantity. All I want is to sense temp and humidity in my humidor, feed it to a PIC and keep it at the right temperature and humidity with a Peltier element. is that asking so much?? ;-) Dale --- The most exciting phrase to hear in science, the one that heralds new discoveries, is not "Eureka!" (I found it!) but "That's funny ..." -- Isaac Asimov -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Dale Botkin wrote: > I know, my $29 Radio Shack thermometer/hygrometer has a sensor in it that > could not possibly have cost more than $.50 in any sort of quantity. All > I want is to sense temp and humidity in my humidor, feed it to a PIC and > keep it at the right temperature and humidity with a Peltier element. is > that asking so much?? ;-) Hi Dale, I'm good at cheap solutions! ;o) Go see your local TV/VCR repairer, ask or beg for a "dew" sensor from just about ay old VCR. If he is friendly he will find one from an old scrapped VCR and probably donate it to you, or just charge a couple of bucks. They are resistive, about 1200 ohms at normal room humidity if I remember right. -Roman PS. If you can get an old scrapped VCR I can tell you where the sensor is, heck you can even pull the sensor from your own VCR and replace it with a resistor, most of the newer VCRs don't bother with a sensor anyway. It is one of those older "quality" features. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Hi Roman, do those dew sensors measure RH or condensed moisture (wet tape)? Allan Roman Black wrote: {Quote hidden}> > Dale Botkin wrote: > > I know, my $29 Radio Shack thermometer/hygrometer has a sensor in it that > > could not possibly have cost more than $.50 in any sort of quantity. All > > I want is to sense temp and humidity in my humidor, feed it to a PIC and > > keep it at the right temperature and humidity with a Peltier element. is > > that asking so much?? ;-) > > Hi Dale, I'm good at cheap solutions! ;o) > Go see your local TV/VCR repairer, ask or beg for a > "dew" sensor from just about ay old VCR. If he is friendly > he will find one from an old scrapped VCR and probably > donate it to you, or just charge a couple of bucks. > They are resistive, about 1200 ohms at normal room > humidity if I remember right. > -Roman > > PS. If you can get an old scrapped VCR I can tell you > where the sensor is, heck you can even pull the sensor > from your own VCR and replace it with a resistor, most > of the newer VCRs don't bother with a sensor anyway. It > is one of those older "quality" features. > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Right, I have a spare parts VCR that has a humidity sensor in it. Its a Mitsubishi HS-337EZ. Problem is the moisure light never goes off ( hence the allocation to the spare parts bin ). Could be the sensor. Any idea what it looks like and what val resistor i can replace it with? John {Quote hidden}>Hi Dale, I'm good at cheap solutions! ;o) >Go see your local TV/VCR repairer, ask or beg for a >"dew" sensor from just about ay old VCR. If he is friendly >he will find one from an old scrapped VCR and probably >donate it to you, or just charge a couple of bucks. >They are resistive, about 1200 ohms at normal room >humidity if I remember right. >-Roman >PS. If you can get an old scrapped VCR I can tell you >where the sensor is, heck you can even pull the sensor >from your own VCR and replace it with a resistor, most >of the newer VCRs don't bother with a sensor anyway. It >is one of those older "quality" features. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Allan wrote: > > Hi Roman, > do those dew sensors measure RH or condensed moisture (wet tape)? > Allan They appear to be printed substrate on a small ceramic plate about 8mm square. The resistance varies depending on how much moisture in the air, ie breathing on it changes the resistance. They are mounted near the head drum on a vertical metal plate on most older VCRs. The National/Panasonic ones are notorious for going off value and causing the dew indicator fault in VCRs about 12-15 years old. The Sharp ones seem to be more reliable. :o) -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

John De Villiers wrote: > > Right, I have a spare parts VCR that has a humidity sensor in it. Its a > Mitsubishi HS-337EZ. Problem is the moisure light never goes off ( hence the > allocation to the spare parts bin ). Could be the sensor. Any idea what it > looks like and what val resistor i can replace it with? > > John Ha ha! Try a 1200 ohm resistor, if that doesn't work go to 2200 ohms. Replace the sensor completely with the resistor. The sensor is a little white ceramic thing mounted on a vertical metal plate near the head drum. :o) -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

I think that RH sensors for VCRs can be bought as spare parts. Try a local VCR repair shop. I do not know what range they have, and they are guaranteed not to be linear, but at least there is one in each and every vcr, dat tape, and camcorder (even dv), so there should be spare parts... The only time I played with this I found that they go high Z when humid (esp. condensation). I suppose that one could be calibrated. Standard circuit seems to be 220-330K pullup from 5V followed by simple comparator or A/D measurement. For a single, strip a dead VCR and look in the schematics for the exact value of the pullup resistor. I suspect that a lower resistor value will not do it much good. Since these go bad once in a while, it is a good idea not to rely on them too much imho. Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body