New to electronics, designing water temp sensors circuit for PC use, need ideas

[pearlyred]

Hi folks,

I'm fairly new to the electronics scene, having just dabbled with a few basic things in previous years.

What I'm looking at doing as a home project is creating a 'box' which can accept various sensors (temp, ph etc) for measuring water parameters.  I want this to connect to a controlling pc where the data will be displayed etc.

Since theres so much I need to learn, I figured I would do this a bit at a time, starting with temp.

So.. any ideas on how I could create some sort of waterproof temp sensor which I could use to send data to a pc?  Probably using the LPT port?  If I can learn how the circuit will work I can create some software for it.  I'm a little more comfortable with this part. It'll use a mix of VB and C++.

Parts of this are probably already available, but i'd really like to learn and do my own from scratch if i can, just need a helping hand to get started.

Cheers
Lee

[Kain]

The simple way this is usually done is by using AD convertor so you are able to send analog data to the LPT or any port that you might be using. So you should be using AD convertor and interface it to the LPT (LPT is easier  ;D).

[MP]

Without a little extra HW and SW, the LPT port will normally give you an 8 bit word. Is this all you need? If so, you can use something like a LM34 or LM35 in a sealed case setup to send a predetermined voltage signal to the parallel port. Feed this voltage to a set of 8 comparators which will make up a simple A/D converter. Then all your software program in the pc will need to do is to read the port. You can also use an LM3914 for this purpose. Then you would have the choice of using dot mode. (See LM3914 data sheet).

To interface to the serial port, you will need a micro connected to the sensor. The pc will expect data bits, stop bits, and parity from the sensor circuit to be the same as selected in the pc.

MP