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

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 02:34:14 2003