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

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 Tue Oct 21 15:11:32 2003