Interfacing RS232 / I2C

[Greg T]

Gidday,

I'm trying to figure out if I can build a simple (read:cheap)
temperature sensor by connecting an I2C compatible sensor ship (like the
LM92) to an RS-232 port and get something meaningful out of it.

A circuit diagram located at
http://www.eidusa.com/Electronics_Kits_RS232_To_I2C_TEMP.htm seems to
indicate that this can be done without a MAX232 or other IC, but other
places are selling RS232-I2C convertors for upwards of $200.

Are there any other good sources of information about such interfaces?

thanks,
Greg

 

[Robert Baer]

Gidday,

I'm trying to figure out if I can build a simple (read:cheap)
temperature sensor by connecting an I2C compatible sensor ship (like the
LM92) to an RS-232 port and get something meaningful out of it.

A circuit diagram located at
http://www.eidusa.com/Electronics_Kits_RS232_To_I2C_TEMP.htm seems to
indicate that this can be done without a MAX232 or other IC, but other
places are selling RS232-I2C convertors for upwards of $200.

Are there any other good sources of information about such interfaces?

thanks,
Greg

I do not know anything about the I2C protocol or voltage levels.
If the levels are at least 3V apart, then driving RS-232 is possible.
One would need to write a special routine, and AFAIK all of the GUIs
are jealous masters concerning I/O, making that task almost impossible.
In any event, one could use one of the hand-shaking lines (to bypass
the UART); either pin 5 CTS, pin 6 DSR or pin 8 CD will do.
Do not use any Maxim parts in a design; most of what they advertise
is vaporware.

 

[Andy P]

While you can do the RS232-I2C thing relatively cheaply, most of it has
to be done in software on the computer, and it's a pita. I have done it
, but the circuitry gets pretty complex thanks to the bi-directional
nature of the protocol, and it's inversion relative to the pins on the
serial port.

The easiest implementation (without a microcontroller) I've seen is the
parallel port. It requires only a buffer IC and software
implementation. When working with windows NT,2k, or xp you will need
something like DLportIO (google it). If working with 9x series windows
you can directly access the hardware. Linux already has numerous
programs written to do it, or you could write your own. Macs I ahve no
idea about.


In the end, I would reccommend using a microcontroller. You could use
soemthing like a Picaxe to make it relatively simple as it's jsut
programmed in a version of basic, and has RS232 and I2C built into it.


--Andy P

 

[Greg T]

Gidday,

I'm trying to figure out if I can build a simple (read:cheap)
temperature sensor by connecting an I2C compatible sensor ship (like the
LM92) to an RS-232 port and get something meaningful out of it.

A circuit diagram located at
http://www.eidusa.com/Electronics_Kits_RS232_To_I2C_TEMP.htm seems to
indicate that this can be done without a MAX232 or other IC, but other
places are selling RS232-I2C convertors for upwards of $200.

Are there any other good sources of information about such interfaces?

For anyone else who's keen on a simple serial port sensor:

I found what I was looking for at http://www.lancos.com/webtherm.html,
which includes schematics for a simple DS1621 sensor -> RS232 interface,
including source code for the driver.

Thanks to those who have replied,

Greg