And please say exactly what it is you need help with.

Also, kindly refrain from making three posts in a row as I find it very annoying.

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Ok Chaps, thanks for all your help so far, but i have to admit that my knowledge and understanding in this area is very limited and i am trying to do something a bit above my level, none the less, i still want to give it a go.

I have attached my circuit (i think) for measuring the capacitance, where cx is the unknown capacitor that is being created in the oil. Sorry about the missing values (and even the ones that are there might be a bit wrong, i'm afraid i have left my diagram somewhere.)

I am prob expecting this to be much simpler than it is, but what i was hoping for was some sort of addition to my circuit that would allow me to basically plug my circuit into my computer and i would be able to see (and manipulate) data.
By the sounds of thins HANKS liberty basic and just basic suggestion are the closest to what i was looking for.

But i have to confess i don't know what RS-232 is?
Also, is the parallel port that cable with the screw things in it?

I have searched RS-232 on sites such as maplins and RS and have found millions of items ranging from pennys to hundreds of pounds and really don't have a clue what i am looking for.

If its not too much to ask, can you break things down for me as i am a bit slow.

Oh and by the way, i'm not a 'he' i'm a girly

Attached Images

cap.GIF (6.6 KB, 20 views)

 

Ah, so is this 'Dual channel 12bit A/D convertor type MCP3202' like a component that i can add on to my circuit? If it is, that sounds good. If not, how do i use it?

 

Hello ? ? ?

 

RS232 is a standard for voltages when sending serial data between systems.

You could use the MCP3202, but since most of the microprocessors include ADCs, it's probably not necessary to have a separate one. A separate one would be needed if you actually want up to 12-bit accuracy.

Look at the smaller PICs and AVRs with ADC and serial ports.

I think you can get some good beginner information on Jan Axelson's site.

 

Hi again Helz15
Ok, let's see if we can get you up to speed with a sort of "computer ports primer"... *very deep breath*

First detail in case you didn't know it: all the ports described here use digital signals of one form or another, rather than analogue. I trust you understand this ok so I won't go into it further here.

RS-232 is the electrical standard used on computer "serial ports", aka "com ports". So the terms are often (perhaps wrongly?) used interchangeably. Most computers will have 2, 1, or maybe 0 (on very modern ones) serial ports! If you have any 9 pin "D-plugs" (see later images) around the back of your computer, probably next to your "parallel port", those would be serial ports. Note that the 2nd serial ports of some MUCH older computers have 25 pins instead, which can make those ones quite easy to confuse with the parallel port To interface with a serial port, it's easiest to use the MAX232 (or similar) chips mentioned, because RS232 uses quite odd voltages and these chips convert those signals to and from the 0/5V ones we often prefer to use in our circuits. Serial ports have few signal lines: one in either direction for data, which is sent 1 bit at a time, and some others for such details as "flow control". They used to be used for modems, and occasionally for mice.

As you guessed, yes: "parallel ports" are one of the various ones whose connectors have the screws in. They're 25-pin D plugs, and their main use is in connecting (older) printers to the computer, so they're usually just called "printer ports". I mentioned that some very old computers also have 25-pin serial ports- if you have one (you'll see illustrated further on) then you can tell them apart by the gender of the connectors. My own personal, subjective and very very limited experience of interfacing circuits with parallel ports was not too great, but other people have managed ok and plenty of commercial hardware used to use them happily for all sorts of things. There's good reasons why my experience was quite probably irrelevant. Parallel ports use either 0-5V, or 0-3.3V signals (never heard of any other levels but I could be wrong). They have quite a few signal lines, mostly from the computer to the device (because they're mostly for printers).

WHAT THEY LOOK LIKE:

If you have a relatively modern computer with these ports, it should look a bit like this: http://www.vpedal.com/images/two_serial.gif
(colours may vary?) Note that the TOP one there is the "parallel port" or "printer port", hence the printer icon. The other two smaller ones are the serial ports, hence the little "binary stream" icons next to them. That coverplate there ALSO has an icon for "monitor" next to one, because they make such plates for lots of different motherboards, and some would have a different connector there! But VGA monitor sockets do look different enough if you look properly, and you couldn't fit a serial plug into one, so no worries. Eh, unless you bought the wrong type of plug too

If you have a MUCH older computer, your serial ports will probably look like on this page: http://computer.howstuffworks.com/serial-port2.htm
But that's quite a big "if" Obviously though, merely having backplates like that (which almost all PCs have) but with other connectors on them, doesn't mean that those connectors are old serial ports! (Sorry if that sounds too obvious)

As I said, I think SOME new computers don't have ANY RS232 serial ports, and maybe no parallel printer ports either! USB is a very different sort of serial port (actually a "bus") that is replacing them for most new commercial hardware. But it's much harder (not impossible!) for hobbyists like us to work with If you have only USB, and no serial(RS232) or parallel ports at all, you should let us know so we can help figure out what options are available to you. But it sounds as though you do have some anyway??

Ok, sorry that was so very long (maybe I should copy it to a page of my site for future), but it did sound like these details were new to you. Hope it helped!

 

Eh, yes and no, ish. The terms "A/D convertor", "ADC", and various others, refer to an "analogue to digital convertor" (eh, "analog" if you're American I guess). They take an analog signal (normally a voltage, BUT you can get some ADCs which also read a current directly; I don't know if these are as common but it shouldn't matter...) and convert it into digital data (IE: 1s and 0s, expressed in whatever manner), which is then more compatible with your computer's ports. That's not all you'd have to do to get it into the computer, you'd need to get it the right voltage levels etc too and maybe send it in serial (bit-at-a-time) fashion too, but...

As for that "yes and no, ish" answer, well ADCs come in various forms. The MCP3202 mentioned would be a single component to use in your circuit, yes. It'd be an integrated circuit (IC, a chip) like your 555 timer. But you can also get other brands and types of ADC, and you can build them yourself from parts (with effort), and many microcontrollers come with them built-in.

Here, BTW, is another quite different idea, as all this might be getting a bit much for you perhaps, I dunno. You quite surely either have a sound card in your computer, or else on-board sound stuff built into the motherboard. AFAIK, basically all the interfaces for these also have a 15-pin port for joysticks (and also for MIDI), apart from the audio plugs. Yes, it's a bit odd that these are on sound cards, but that's not my fault Anyway, the joysticks these work with use variable resistors basically. So the joystick ports are already designed to read analogue levels, if you can get the signals into a form that the ports will like. Your basic programs would PROBABLY be able to read the values from ports, although they'd probably also need calibrating somehow, and I don't know how hard that would be.

I don't know exactly how doable this is though, in terms of hardware or programming. And very little sense of how to go about it. Anybody got any ideas? Could the current be sent directly if suitably scaled? I expect it'd read out nonlinearly if so?

 

hi heltz,
Has Tomble answered your question OK, or do you want more information?

The MCP3302 connects to the PC's printer port and controlled/output as SPI using a program in the PC.

Get the datasheet for the MCP3202 from www.datasheetarchive.com

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Thanks Chaps,

I think that is enough information to get me going, but i'm sure i will be back.

Many thanks for all your help, its very much appreciated.

H.

 

Hey cool, good luck!

BTW, did anybody have any thoughts on my joystick port suggestion up there? It may easily have got buried in the monstrous heap of info I'd gone and posted (sorry!)

 

For RS 232 you can use MAX 232 IC, this converts TTL voltage levels to RS 232 +12/-12 levels.

But I think you will still need a mcu for this, as RS 232 sends/receives ASCII characters, you could also develop a program in C to toggle the RS 232 port lines (namely RTS, DTR etc).

If you are not interested in a mcu, you might find the parallel port easy to use, as the port contains several output pins and input pins. Control of these pins can be easily done through software.

thanks
a

 

Hi guys,

I have another question to go with this project.

Will i need a buffer in the computor to store information?
I was thinking of sending the infomation every couple of seconds.

Thanks

H.

 

There are multimeters with a port connection built-in. few of them were reviewed in the Elektor magazine in one of their recent issues.

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Does this mean if i replace the AVO (to measure current) on my circuit with a resistor and measure the voltage over the resistor using one of these mulitmeters i can basically plug it straight into the computer?

If this is the case, this sounds excellent, however, i don't think i will be able to do that, as this is a college project and it may make it a bit to 'thin on the ground'.
Although it may be good for testing the initial part of my circuit.

I may have simplified this too much, but it think the basic stages involved in my project are:

- Set up the circuit as shown in the diagram (attached to a previous post)
- Replace the AVO with a resistor (don't know what size) to get a voltage reading.
- use an A/D converter (although i think this is in the chip)
- use a MAX232 chip to make it that RS232 thing
- plug into parrallel port
- use a buffer to store data

Have i understood what i have been told, or am i missing something?

I was also reading through other posts to see if i could find anything simular and i found one where someone was talking about using an AVR or PIC microprocessor as a local controller.
It said this would do the A/D conversion at a specified interval and log the data.
Would this be suitable for my project?

Thanks.

 

try ICL7109 applications and it should be possible to make a device to work with PC

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