Newbie: A/D -> RS-232 -> Computer -> RS-232 -> D/A

R

Ralph Seguin

Guest
I'm interested in learning electronics (have picked up a basic book,
but open to recommendations).

Anyhow, I'm basically looking for some help on the
best/easiest/cheapest/fastest way of reading some analog values into
the computer (via USB or RS-232 port), processing these values and
then outputting a value via USB or RS-232 port to be output in analog.
I'm also interested in outputting a value that represents a frequency
to be generated by a timer chip.

Help!?

I've done some looking on Digikey and there are piles of A/D and D/A
chips with serial interfaces on them. These are clearly not meant for
RS-232 direct interfacing and I'm sure are meant for high speed serial
input.

I'm open to using PIC chips if necessary. If that is the route, then
I need to find an inexpensive source for them.

So, I guess I'm asking somebody/everybody to give me free
ideas/designs that would normally cost mucho $$$ :)

Thanks.
-Ralph
 
"Ralph Seguin" <rpseguin@yahoo.com> wrote in message
news:63ca7e76.0401132100.6ba2e8e1@posting.google.com...
I'm interested in learning electronics (have picked up a basic book,
but open to recommendations).

Anyhow, I'm basically looking for some help on the
best/easiest/cheapest/fastest way of reading some analog values into
the computer (via USB or RS-232 port), processing these values and
then outputting a value via USB or RS-232 port to be output in analog.
I'm also interested in outputting a value that represents a frequency
to be generated by a timer chip.

Help!?

I've done some looking on Digikey and there are piles of A/D and D/A
chips with serial interfaces on them. These are clearly not meant for
RS-232 direct interfacing and I'm sure are meant for high speed serial
input.

I'm open to using PIC chips if necessary. If that is the route, then
I need to find an inexpensive source for them.

So, I guess I'm asking somebody/everybody to give me free
ideas/designs that would normally cost mucho $$$ :)

Thanks.
-Ralph
Click to expand...

What I started reading your post I was hoping to see you mention the PIC (or
any other MCU), which you did! That's because the MCU approach is one of the
easiest and most flexible. You can get PICs with built-in A/D converters of
up to 10 bits or resolution. As for D/A, if you're not too bothered with
issues like precision, speed and ripple, you can use one of the built-in PWM
outputs to generate an analogue voltage using a simple RC filter. The
resolution of the h/w PWM modules on standard PICs goes up to 10 bits too,
which matches the A/D nicely. If you want to go for a true D/A chip, there
are plenty available. Choose a serial one (to save pins) and drive it from
the PIC's pins directly. For the serial (RS-232) communication there are
PICs with built-in USART modules that do it in hardware. I'd suggest the
16F877A as a general purpose PIC with all of the above. If it's too big for
you (40 pins) you can get the 28-pin version (16F876A). If you finally
decide to go the PIC way, do a Google search for programmers, resources,
etc. The available information is overwhelming. I personally use the ePIC
programmer from http://www.melabs.com/. As for source code, check out
http://www.piclist.com.

Once you build the data acquisition circuit and you can send/receive
analogue signals, you can use the remaining PIC pins and code memory to do
all sorts of fancy stuff like driving LCDs, controlling motors, etc. A nice
beginner/intermediate project is to build a servo position control system
with a motor coupled with a pot to provide the feedback signal.

Good luck.

Costas
_________________________________________________
Costas Vlachos Email: c-X-vlachos@hot-X-mail.com
SPAM-TRAPPED: Please remove "-X-" before replying
 
There are lots of simple A/D interfaces available to buy if you don't want
to design your own.

Try a search on "data logging" or see these pages...

http://www.picotech.com/
http://www.picotech.com/data.html
 
On a sunny day (13 Jan 2004 21:00:49 -0800) it happened rpseguin@yahoo.com
(Ralph Seguin) wrote in <63ca7e76.0401132100.6ba2e8e1@posting.google.com>:

I'm interested in learning electronics (have picked up a basic book,
but open to recommendations).

Anyhow, I'm basically looking for some help on the
best/easiest/cheapest/fastest way of reading some analog values into
the computer (via USB or RS-232 port), processing these values and
then outputting a value via USB or RS-232 port to be output in analog.
I'm also interested in outputting a value that represents a frequency
to be generated by a timer chip.

Help!?

I've done some looking on Digikey and there are piles of A/D and D/A
chips with serial interfaces on them. These are clearly not meant for
RS-232 direct interfacing and I'm sure are meant for high speed serial
input.

I'm open to using PIC chips if necessary. If that is the route, then
I need to find an inexpensive source for them.

So, I guess I'm asking somebody/everybody to give me free
ideas/designs that would normally cost mucho $$$ :)

Thanks.
-Ralph
The PIC 12F675 has a 4 channel AD, 8 pins, you can use a pin
Click to expand...
for serial out, internal flash memory, internal oscillator and cost
about 2 $ in single quantities.
So:
2 power pins (+ and GND)
4 input pins
1 reset pin
1 serial out

To do the D/A spend an other 2 dollars and use the timer in that
chip to generate a PWM signal, that you then lowpass with a simple RC.
Rest as above.

For that money buy 10 and start experimenting.

Some (much) more expensive pics have rs232 port, some are 'self
programable' via the rs232.


You can also use a Philips PCF8591 on 3 pins (2 for sda, 1 for scl),
it has 4 channel A/D and 1 channel DA 8 bits, but not true rs232,
but i2c.
 
"Ralph Seguin" <rpseguin@yahoo.com> wrote in message
news:63ca7e76.0401132100.6ba2e8e1@posting.google.com...
I'm interested in learning electronics (have picked up a basic book,
but open to recommendations).

Anyhow, I'm basically looking for some help on the
best/easiest/cheapest/fastest way of reading some analog values into
the computer (via USB or RS-232 port), processing these values and
then outputting a value via USB or RS-232 port to be output in analog.
I'm also interested in outputting a value that represents a frequency
to be generated by a timer chip.

Help!?

I've done some looking on Digikey and there are piles of A/D and D/A
chips with serial interfaces on them. These are clearly not meant for
RS-232 direct interfacing and I'm sure are meant for high speed serial
input.

I'm open to using PIC chips if necessary. If that is the route, then
I need to find an inexpensive source for them.

So, I guess I'm asking somebody/everybody to give me free
ideas/designs that would normally cost mucho $$$ :)

Thanks.
-Ralph
Click to expand...


Go to http://www.dataq.com/194.htm

It's $24.95 with all the software you need, and there are 4 10Bit channels.

Least expensive I've found! I have three I use for DC power supply
monitoring.
 
rpseguin@yahoo.com (Ralph Seguin) wrote:

I'm interested in learning electronics (have picked up a basic book,
but open to recommendations).

Anyhow, I'm basically looking for some help on the
best/easiest/cheapest/fastest way of reading some analog values into
the computer (via USB or RS-232 port), processing these values and
then outputting a value via USB or RS-232 port to be output in analog.
I'm also interested in outputting a value that represents a frequency
to be generated by a timer chip.

Help!?

I've done some looking on Digikey and there are piles of A/D and D/A
chips with serial interfaces on them. These are clearly not meant for
RS-232 direct interfacing and I'm sure are meant for high speed serial
input.

I'm open to using PIC chips if necessary. If that is the route, then
I need to find an inexpensive source for them.

So, I guess I'm asking somebody/everybody to give me free
ideas/designs that would normally cost mucho $$$ :)

Thanks.
-Ralph
Click to expand...
Monitoring analog data via an RS232 connection is the easy part. DATAQ has a 4
port, 10 bit, A/D device that gets its operating power from the serial
connection to the PC and includes some software. They even include some VB
source code. http://www.dataq.com/194.htm
$24.95US

More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter at@at mindspring dot.dot com. Fix the obvious to reply by email.
 
On 13 Jan 2004 21:00:49 -0800, rpseguin@yahoo.com (Ralph Seguin)
wrote:


I'm open to using PIC chips if necessary. If that is the route, then
I need to find an inexpensive source for them.
Click to expand...
Now we're talking 8)

For your objective i'll suggest the pic 16f877 or the 16f877a.
They both have a UART (or USART?! i'm not sure) and a ADC included.

Go for www.microchip.com and find its datasheet...

For programming the PIC, I'm using the "Trivial Low Voltage
Programmer" TLVP circuit *free* : it's bloody simple and works

look at http://www.finitesite.com/d3jsys/

(you still need to get a aditional circuit for the +5V supply for the
programmer ... not included above. A simple +9V power supply and a
voltage regulator / 5.1 zener diode will do the trick ...)

On the same link above is the software to use the programmer (free)

I think the best free programmer solution would be the
http://www.voti.nl/wisp/index_1.html
but if you want to quickly start PIC programming, i'ts the simplest
yet working circuit i've found.

A word of warning : if you want to try the TLVP, stick to the 16F877
instead of the 16F877A ... the first chip is a lot bulkier that the A
version but I haven't found the software needed to program the A
version chips ... Although the http://www.voti.nl/wisp/index_1.html
can.

Note that with the programmer you can use every language you want :
BASIC, C, asm, whatever. The programmer only takes your compiled code
(compiled by your language compiler) and puts it into the PIC flash
epprom !

Be carefull when building the hardware ... Check everything, specially
the PC parallel port wiring ... Don't blow up your PC parallel port 8)

For the PC paraller port wiring, look at http://www.hardwarebook.net/


Ufff! I hope I've helped you 8)
Information overload ?! 8) hope not !
 
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