Re: Q: 5V<->12V level conversion

Henrik,

Firstly, I'm not ignoring you but your probably close to the mark
about me not understanding and for that I do appologise. I am
incredibly thankful for the input, suggestions and patience you and
others have shown.

Using the MAX232 was a suggested alternative from a different group
(attached below). BTW, no RS232 line is connected directly to the
AVR but rather are going through the MAX.

My mistake was sending the previous post regarding this alternative
without doing any research.

My first search returned the following usenet post in
sci.electronics.basics "Yes - one RS-232 transmitter should be able
to drive a few receivers. However, you cannot have multiple
transmitters talking on the same wire."

I'm am definately going to persist with the my first (multiple
transistor) design as it seems the most logical to me.

Based on suggestions from yourself and others I hope to open source
the adapter and some of the Java code I've been writing.

Thanks again all of you for your input!

Regards,
Adam Bradley

---snip---

From: "Tom Deutschman" <autotraxeda@t...>
Date: Wed Oct 22, 2003 10:13 am
Subject: Re: Q: 5V<->12V level conversion (please check!)

Hi Adam,

You might want to consider using a Maxim (www.maxim-ic.com) RS232
converter IC. Check out this link:

http://para.maxim-ic.com/compare.asp?
Fam=RS232&Tree=Interface&HP=Interface.cfm&l\n=

As you'll see, they offer many different models, 3V and 5V supply, all
will handle the 12VDC from the car. An added bonus is the ESD
protection on the inputs. To use the transmitter, I assume you want to
convert from 5V to 12V as well, put a diode in series with the output
of the Maxim (or other RS232 transmitter) with the cathode pointing
towards whatever 12V receiver you are communicating with.

As far as converting from 12VDC to 5VDC, the RS232 receiver will
handle this nicely. Doesn't matter that your input signal is between
0V and 12V. The RS232 receiver will handle this ok.

Maxim also offers free samples of most of their parts in both SMT and
through hole.

---snip---

--- In opendiag@yahoogroups.com, "alfatok" <hi.johnsson@t...> wrote:
> --- In opendiag@yahoogroups.com, "Adam Bradley"
<adam_j_bradley@y...>
> wrote:
> > And now for something completely different!
> >
> >
http://members.optushome.com.au/adambradley/electronics/LevelConverter
> > /V12/LevelConverter-v12-ajb.jpg
> >
>
> I don't know why I bother, you doesn't seem to read/understand what
I
> try to tell you. Oh well...
>
> I can't figure out what you hope to accomplish with that design,
but I
> can tell you what it will do. It will ruin a perfectly good AVR.
> Possibly the MAX 232 too. You have connected a RS232 output to a pin
> on the AVR and the AVR does not respond well to the voltages
involved.
> The little loop with the diode may very well start to oscillate.
>
> Was it your plan to use the MAX 232 to interface towards the K-Line?
> That's definitely not a good idea. RS232 is not intended to work
with
> several drivers on the same line, you might end up with a bus
> collision where you would possibly blow the MAX 232, or in worst
case
> damage the ECU. Since the K-line has multiple drivers it shall be
> driven with open collector drivers. And the receiver in the MAX 232
> will not reliably read (if at all) the levels on a K-Line.
>
>
> > --- In opendiag@yahoogroups.com, "Adam Bradley"
<adam_j_bradley@y...>
> > wrote:
> > > Possibly the final at
> > >
> >
http://members.optushome.com.au/adambradley/electronics/LevelConverter
> > > /V10/
> > >
>
> That design is still a mess and now it seems you've managed to
invert
> both TX and RX. Maybe I don't understand your application, but I'm
> pretty sure that it's not the way it should be. On the other hand,
if
> you're going to use that particular AVR (as used in V12) you'll have
> to bit bang the serial data and then you can get away with it by
> inverting all data bits as well as start and stop bits and of course
> the idle polarity. Quite doable, but why not follow established
practice?
>
> Honestly, apart from not being isolated, I think the inital design
you
> asked about (the one with only one transistor) was pretty neat. Why
go
> through all this trouble with designing your own?
>
> /Henrik

 
Received on Sat Oct 25 01:23:35 2003