Does anyone know where I can get a cheap temperature sensor with a RS232 output ? I have now moved my server out into my garage as we discussed here a few months ago. All seems to be fine so far, it has been out there for about 8 weeks so far. I am currently using a small cheap max/min thermometer, which tells be the temperature has stayed between 5°C and 21°C. It never appears to vary by more than 10°C over a 24 hour period.

However, I would like a more useful monitoring system, so I have been looking for temperarure sensors that I can plug into the serial port on the server (I want to throw the data at mrtg to give me pretty graphs). The problem is that everything seems to be so expensive as it is aimed at industrial uses. I refuse to pay $150+ for a thermometer ! I don't need this think to be stunningly accurate, I am more interested in changes in the temperature rather than the absolute temperature anyway.

So, does anyone out there know of any cheaper RS232 temperature sensors ?

I would like to measure humidity as well, but the prices for humidty sensors seems to be even worse.

Failing that, does anyone have a schematic for a simple circuit that I could build to provide this functionality ? (if I can remember where I put my soldering iron)

By the way, the cheapest RS232 sensor I have found so far is this one:

http://www.weathershop.com/temptrax.htm

$129 + $40 if you want a second probe.

What is silly is they sell fancy wireless weather stations with big displays for half the price:

http://www.weathershop.com/lcm_ws7014u.htm

I guess it is all about volume, can't be too many people out there buying RS232 sensors...

Hmmm. I don't have the solution your asking for, but have you checked out iButtons? (www.ibutton.com). They look really cool and I've been wanting to play with them for months now but havn't found an excuse.

One of the many buttons they offer is a time/temperature logger that can actualy be seperated from the computer. For your purposes I'd assume you could just tape it to the reader and forget about the mobility aspect.

The starter "thermochron" button kit is $25, which seems to be a much better deal than what you've found so far. Let me know if you try it out, I'd love to hear how they work in practice.

Matthew

Yes. The 1-wire stuff from Dallas is quite cool. If you've got a PIC/AVR stuff than it's just easier to use one of those to interface it to the serial port. As most of the other cheap iButton/1-wire adapters require you to do bitbanging on the serial or parallel port.

Unfortunately you'll probably end up using the same chip as the empeg uses so if you're not very careful you can put it into thermostat mode. But then again since it is a large package you can just chuck it or reprogram it if you've got the time.

I've got a Dallas iButton developer kit at home and it is quite neat to play about with

- Trevor

Andy,

What's the OS on the Dell in the garage? I'm just thinking of a few different ways to do the same thing. Would it suffice to log temp data on that server and be able to view it....or have it mail you temp data?

The OS on the Dell is Win2k Advanced Server, but my Linux server will be joining it in the garage soon.

I was expecting to write some of my own code anyway, just some simple perl or VB to pull the data off of the COM port and feed it to MRTG.

Software I can do, hardware is more of a struggle. Where is that damn soldering iron....

visit PH Anderson's web page.
This link in particular has the product I'm thinking of, and he says he has a complete assembled kit on a Breadboard for $50 - which is half of another product quoted on this BBS.


He offers kits of various products including Dallas 1-wire temperature sensors that can report to a serial port the readings.

I think you'd find something there you could use, admittedly its not all a nice little box you buy, a few people here could build one for you for a few dollars if you ask them nicely and use these kits.

The site has detailed info on what the data looks like so you can knock up your VB program.

Some of the kits allow you to have to have multiple sensors and you could even keep the temeperature sensors in the garage but have the electronics in your house somewhere near your PC thats gathering the data. [Thats the beauty of the Dallas 1-wire stuff - it does the conversion of temperature on-board and can send the temperature reading data down a single pair wire to the PC some distance away.]