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

Possibly the final at
http://members.optushome.com.au/adambradley/electronics/LevelConverter
/V10/

Adam

--- In opendiag@yahoogroups.com, "Adam Bradley" <adam_j_bradley@y...>
wrote:
> Updated schematic (with simulation pictures!) at
>
http://members.optushome.com.au/adambradley/electronics/LevelConverter
> /V2/
>
> Please keep those comments rolling in!
>
> Adam
>
> --- In opendiag@yahoogroups.com, "Adam Bradley"
<adam_j_bradley@y...>
> wrote:
> > Henrik,
> >
> > I've uploaded a couple of images of my schematic in which a TTL
> high
> > and low (5v and GND) are injected into the circuit.
> >
> > Once again the two files are in
> > http://groups.yahoo.com/group/opendiag/files/AJB/
> >
> > and called
> >
> > 5V connected to TTL Tx.jpg
> > 5V disconnected from TTL Tx.jpg
> >
> > The multimeter reading is taken from the K line.
> >
> > Any ideas how this works?
> > :)
> >
> > Adam
> >
> > --- In opendiag@yahoogroups.com, "alfatok" <hi.johnsson@t...>
wrote:
> > > --- In opendiag@yahoogroups.com, "Adam Bradley"
> > <adam_j_bradley@y...>
> > > wrote:
> > > > Henrik,
> > > >
> > > > After a bit of bashing about I've made a couple of changes
that
> > make
> > > > the circuit a little better. Rather than a voltage divider,
> I've
> > > > used a pull down resistor to tag the voltage at either 0V or
5V
> > > > irrespective of the input voltage (almost anyhow!).
> > > >
> > > > Can you have a look at
> > > >
> >
>
http://members.optushome.com.au/adambradley/electronics/LevelConverter
> > > > /LevelConverter-v7d-cnv-candidate.jpg
> > > >
> > > > Also, if I want to optoisolate this circuit (in both
> directions)
> > is
> > > > all that is required to add two opto's on both the Rx and Tx
> > lines?
> > > >
> > > > and let me know what you think?
> > > > Thanks!
> > > > Adam
> > > >
> > >
> > > Took a while to grasp, but the only way I can make sense of
that
> is
> > if
> > > you have turned the Q1 symbol upside down. The battery symbols
are
> > > definitely turned the wrong way. If my suspicion about Q1 is
> > correct,
> > > then it will act as an inverter, high on K-line gives low on Rx
> > which
> > > is not the way the original design worked and not the way Tx
> works.
> > > But maybe I'm wrong. As I said, I'm not very good at this stuff.
> > >
> > > Actually, if you're going to run the entire design powered from
> the
> > > electrical system in the car, opto isolation might not be such
a
> big
> > > issue. If you look at the design I pointed out in my previous
post
> > > you'll see that it takes two opto isolators and you will
probably
> > need
> > > to have two transistors on the K-line side. You must make sure
the
> > > uController Tx line is capable of driving the LED in the opto
> > > isolator, otherwise it must be buffered. You also have to
> consider
> > the
> > > polarity of the signals. Most schematics that you'll find for
this
> > > kind of interface are designed to be connected to a serial port
> on a
> > > PC where the signals are inverted compared to what you get
> straight
> > > out of the UART. Those designs invert polarity of the data
going
> in
> > > both directions, your design probably shouldn't.
> > >
> > > /Henrik

 
Received on Wed Oct 22 03:35:13 2003