pearlyred said: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
Where would I start if I wanted to make my own sensor, any ideas?Optikon said:For very little cost, you can build your own waterproof temp sensor and interface electronics so your VB program can get readings.
Sorry to be stupid, but could you explain that a little. Isolated from what?Optikon said:There have been numerous parallel port interface circuits shown here on this forum (search for them). Just make sure to pick one that is isolated for an easier time with debugging.
Sounds like it is easier to go with an analog output and use a ADC with LPT, than it would be to find a digital output sensor? I figured LPT would be better as its faster, but in your opinion which offers the best control of devices, bearing in mind I eventually want several sensors etc in the device?Optikon said:1) Temperature is an analog quantity and as such if your sensor provides and analog voltage, this will be much more complicated to get into a computer. An analog to digital conversion must take place and that really complicates the design(relatively speaking).
2) You can find digital output temperature sensors but the ones I have seen are serial output. I've never come across a parallel "flash" type of temperature converter although, that would be neat. So you will have a serial temperature stream. You will need to do a serial to parallel conversion to get it in the right format for an LPT port. Maybe this is not a big deal, but maybe using the serial port gives you an advantage in this regard. I think it really depends on how much design work you want to do.
Yes, this needs to be accurate, at least 0.5 degrees C. You lost me after that bit I'm afraid. Just how much does it complicate things, in terms of cost and design difficulty?Optikon said:3) You did not specify how accurate you need to measure the temperature. If you desire very good accuracy (< 0.5 degree Celsius) or better, it drastically changes the game. For you will likely need to use cold junction compensated thermocouples as your sensor. And the math needed to compute a reading gets ugly with ITS-90 curve fitting 9th order polynomials.
pearlyred said:Sounds like it is easier to go with an analog output and use a ADC with LPT, than it would be to find a digital output sensor? I figured LPT would be better as its faster, but in your opinion which offers the best control of devices, bearing in mind I eventually want several sensors etc in the device?
pearlyred said:Assuming I go with these, can anyone think of any other special components I may need for the circuits, or any major problems I might come across?
pearlyred said:If serial is the easier way to go then I'll do that. At least for now anyway. USB in the future maybe?
pearlyred said:Blimey! These PIC's are seriously involved man.
Looked at the data sheet, may well go with the 16F88, only a couple of dollars more expensive so may aswell.
Programmers and software, there are millions! How do you ever pick one? Is it viable to make one myself from someones design or will I have to buy one ready made? I'd quite like to keep costs minimal.
I dont mind having a go, I just seriously don't know which one to start with. Any good ones you can recommend for that PIC that have readily available designs or retailers?
eblc1388 said:But as yet it does not cover the programming of the 16F88.
The next suitable software is IC-Prog which covers the 16F88 but only allow user to select one of the programmers on its approved list. I can't find P16PRO40 on their approved list.
Any suggestions, guys?
That's very good news for pearlyred indeed.Nigel Goodwin said:The latest working version supports the 16F88, it's not been released yet because I'm still working on 18F support, but I'm happy to email to anyone who wants to use the 16F88.
Nigel Goodwin said:You need to select another option, I'll check what it is when I get home later, but I suspect someone will post the details before then?.
pearlyred said:Ok, well I've been looking around at whats available locally and I can source a LM335Z 3 Pin TO 92 Temp sensor and as far as PIC's go, I know nothing about them but can get either a PIC16F84A-20P or a PIC16F628A-20P or for a little more $$ a PIC16F88. Dont know how far I need to go with these, are any of them easier to program etc than others, or are they designed for different things?
Assuming I go with these, can anyone think of any other special components I may need for the circuits, or any major problems I might come across?
If serial is the easier way to go then I'll do that. At least for now anyway. USB in the future maybe?
Thanks for all the help so far!
LS
Optikon said:Just so you know, LM335 accuracy will NOT achieve what yo mentioned earlier (you said at least 0.5 deg C)
Optikon said:I dont want you to be disappointed if you really need the temp accuracy which, you said you did. (<0.5 error)
pearlyred said:Just another thought, does the wire length between either the device and sensor, or the device and pc make any difference to overall result?
With regards to the A/D what does the resolution mean? The PIC16F88 has 7 channels of 10-bit Analog-to-Digital (A/D) converter. Is this the same thing or something else?
eblc1388 said:Optikon said:Just so you know, LM335 accuracy will NOT achieve what yo mentioned earlier (you said at least 0.5 deg C)
The typical error at the two ends of temperature range is only 0.5 degree and that means from -40 degree to +100 degree, when the LM335 is calibrated at 25 degree. When the temperature to be measured is closer to 25 degree, the error is even smaller.
Optikon said:I dont want you to be disappointed if you really need the temp accuracy which, you said you did. (<0.5 error)
So, please suggests a better solution for pearlyred and the approximate cost to achieve that.
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