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Temperature Recorder

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crunch53

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Does anyone know of a way to hook up a thermistor or something up to the computer to measure or record the temperature in the room? Right now I am just trying to make something simple and cheap that I can hook up to the serial port, parallel port or USB port. It doesn’t matter where I hook it up as long as it is fairly easy for now Eventually I would like to make or buy a data logger so it would be more versatile and I could do other things with it. (When possible I like to make my own things because their usually less expensive, I can make it the way I want it and I can usually learn a lot from the experience). About 15 years ago with the help of a friend of mine at the time I made a circuit that I think used a 555 and a thermistor circuit that plugged into the joystick port of an old Atari computer. The computer counted the pulses which went faster or slower depending on the temperature. I don't remember much more than that. Right now I want to collect the data say every minute or 5 or 10 and send it to an excel spreadsheet or something to make a graph of what the temperature has been for the last day, week or month. Any help is appreciated.

Thanks,
Mike
 
Hi there can be many ways to do this
Since you want to use the serial port
You can implement following scheme
Thermistor -> Signal Conditioning (this will contain a pull up and pull down reistor depending on the kind of thermistor you are using and characteristics you required) -> Low pass filter (usually of 1ms time constant is good enough) -> ADC -> Digital to RS232 circuit -> computer serial port -> Program to interpret serial port data

If you use a simple microcontroller (like PICs) ADC and RS232 can be implemented using just microcontroller itself)

With using 555 you can do this
Thermistor -> 555 in astable multivibrator mode (thermistor as charging resistor) -> computer parallel port -> program to interpret the meaning of pulses (or pulse time) at computer parallel port and display temperature
 
You cod plug one dirctly in the game port.Since the game port meshures resistonce.

You have 4 alalong chanels on that so you can have 4 termistors.There are also 4 didigtal chanels that can be used for buttions to control it.
 
Crunch - Dataq was offering a very low cost Analog to Digital converter/interface package. It had 4 channels - I forget the sampling rate. It was slow but fast enough to be very useful. The package required a 0 to 10 volt signal so you might need to connect a thermistor to an op amp - I think there is a fair amount of info around to do that. It came with the software and 9 pin serial connetor. I have mine, ready to play with when I get time. Building something similar is quite possible and again, it's likely that there is lots of how-to info available. This approach might simplify your work until you understand the thermistor/op amp part enough to move on.

My guess is that someone has implemented and well documented such an effort with PICs or similar low cost devices. It's possible that my Dataq package is precisely that.
 
Hiya Mike,
One project I have in mind is using 2 ds1923 temp and humidity I-buttons for a data logger. I've just got a copy of visual studio 6 so I can make up a simple computer interface with a pic since the commercial ones are so expensive. For now I'm going to use 2 DS1820's with a 16f877a to take inside and outside temps and display it on a lcd. A few of my neighbours have shown an interest in my projects so when time allows I'll make up a few of them and sell them for a little over cost. But there is a heap of info on the net for digital temp sensors why not check them out.

Just a Thought

Cheers Bryan :D
 
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