Which ADC to RS232?

[Jim Ables]

Please accept my apologies if my initial question on this topic was
misinformed, ie. synchronous vs. asynchronous serial.

Assuming that the MAX186 will not hardware interface to RS232, can
anyone suggest a 12-bit ADC that will?

I have seen this question in the archives, but no answers were
offered.

Might someone with good reference materials come up with a part number
or circuit diagram?

The following circuit is like what I am looking for, but it's 18-bit
and the FFT software application I use is set up for 12.

http://www.reed-electronics.com/ednmag/article/CA159691?pubdate=9%2F27%2F2001&spacedesc=designideas

Many thanks,

Jim

[hamilton]

Jim,

Due to the 8-bit asynchronous serial UART hardware involved with a
standard PC, this will require a hardware UART in the external ADC circuit.

Remember that RS-232 is the +- 12V levels of the RS-232 drivers.
You would still need an RS-232 driver chip on your ADC board as well.

But its the 8-bit asynchronous part of the serial port thats your
problem. Thats why you have not found any in the archives. ( and why you
won't )

There are complete projects / boards available with 8-bit async serial
interface chips. i.e. PIC/AVR/8051 microprocessors interfaced to the ADC.

If you are a PC programmer ( basic, C, Pascal) you can get an DLL that
will give you access to I/O ports on a PC. With access to I/O bits you
can create a software SPI port on a serial or parallel port.

The serial port requires a RS-232 driver, the parallel port is 5V.
The project you linked to is a good example of a software SPI port.
Here are some others <http://www.kmitl.ac.th/~kswichit/>

Please be sure to understand that a bit-banged interface to an SPI port
is going to be slow. Each edge of the SPI protocol will be a line of
code in you software. How many edges will be needed to transfer 12-bits
of data. ( write two edges of the clock line, read one bit of data)

If someone here knows of a low cost asnyc serial interface ADC circuit,
please speak up.

A Google search turns up lots of hits, these hits may give you ideas on
how to refine your search.

Who knows, maybe you will find a new career in micro controllers.

Good Luck,

hamilton



Jim Ables wrote:
> Please accept my apologies if my initial question on this topic was
> misinformed, ie. synchronous vs. asynchronous serial.
>
> Assuming that the MAX186 will not hardware interface to RS232, can
> anyone suggest a 12-bit ADC that will?
>
> I have seen this question in the archives, but no answers were
> offered.
>
> Might someone with good reference materials come up with a part number
> or circuit diagram?
>
> The following circuit is like what I am looking for, but it's 18-bit
> and the FFT software application I use is set up for 12.
>
> http://www.reed-electronics.com/ednmag/article/CA159691?pubdate=9%2F27%2F2001&spacedesc=designideas
>
> Many thanks,
>
> Jim

[Ben Bradley]

On Sat, 10 Jul 2004 23:43:51 +1000, Jim Ables <[email protected]>
wrote:

>Please accept my apologies if my initial question on this topic was
>misinformed, ie. synchronous vs. asynchronous serial.
>
>Assuming that the MAX186 will not hardware interface to RS232, can
>anyone suggest a 12-bit ADC that will?

The short answer is no, because no one makes such an ADC. They all
have parallel or syncronous serial interfaces, none have async (RS-232
is async), and there's no easy way to connect an asynchronous serial
port to a syncronous serial port.

>I have seen this question in the archives, but no answers were
>offered.
>
>Might someone with good reference materials come up with a part number
>or circuit diagram?
>
>The following circuit is like what I am looking for, but it's 18-bit
>and the FFT software application I use is set up for 12.
>
>http://www.reed-electronics.com/ednmag/article/CA159691?pubdate=9%2F27%2F2001&spacedesc=designideas

I was a little surprised to see a direct "ADC to RS232" circuit,
and looking closer, this doesn't use "standard RS232," it uses a few
tricks to make the [I presume] syncronous-interface ADC send data
through the PC-standard 9-pin RS232 interface. But if you do use this,
you can just use the 12 most-significant bits and ignore the other 6
bits.

As Hamilton indicated, ADC's with RS-232 (or plain logic-level
async) interfaces probably don't exist, but there are almost surely
microcontrollers with 12-bit ADC's and async ports that can easily
interface with an RS-232 port, and be powered off it as well, giving
you a one-chip (plus a few diodes and transistors for interface and
level translation) solution. Of course, it's a bit of work to program
the micro and design the circuit, so that's left as an exercise for
the reader. :)

>Many thanks,
>
>Jim

[hamilton]

Ben Bradley wrote:

> On Sat, 10 Jul 2004 23:43:51 +1000, Jim Ables <[email protected]>
> wrote:
>
<snip>
>>Jim
>
>
Thanks Ben,

Jim, If you need help in building something, I and sure you can get
help from the nice people here.

What we would need is "what is it you are trying to do" (TM)

hamilton

[Martin Blume]

"hamilton" schrieb
>
> If someone here knows of a low cost asnyc serial interface ADC
> circuit, please speak up.

Linear Technologies offers with the LTC-1290 a single-chip 12-bit
8-channel data acquisition system that can be very easily
interfaced with a RS-232 of a PC.
German electronics supplier Conrad (www.conrad.de) offers
(? used to offer, I am not sure) a kit (part number 967637 (kit)
967653 (ready-made)) that uses this chip.
It is not a "real" RS-232 communication, it works by toggling and
reading the appropriate RS-232 registers.

HTH
Martin

[Bernhard Holzmayer]

hamilton wrote:

>
> If someone here knows of a low cost asnyc serial interface ADC
> circuit, please speak up.
>
> A Google search turns up lots of hits, these hits may give you
> ideas on how to refine your search.
>
> Who knows, maybe you will find a new career in micro controllers.
>
> Good Luck,
>
> hamilton
>

Lots of years ago, I worked with an 80C537 (an 8051 derivate), which
had 12bit ADC and UART for RS232 on board.

If I remember correctly, the PIC family has a device with on-board
ADC, too. (Small, cheap, easy to use.)

Scan the web for microcontrollers with on-board ADC, and you'll
certainly find a broad range. 12bit should be available.

Most of them should either have hardware UARTs on board, or at least
it should be easy to implement RS232 support in software.

Bernhard