Mobile to PIC TX/RX connection

[hybrid_snyper]

With reference to this earlier post of mine, i was wanting to ask a
quick question. I am in the final stages of my project and I am now
ready to construct the mobile interface. The design that Costas Vlachos
helped me with just needs to some clarifying, there is a zener diode in
this circuit, and i am unsure what zener to choose to perform the
correct conversion of the signal from the RX line, for the time being i
have selected the 1N4678 diode but this is just a guess.

http://groups.google.co.uk/group/sc...q=hybrid_snyper&rnum=2&hl=en#560a336845019a11

Thanks in advance

Wayne

 

[Costas Vlachos]

With reference to this earlier post of mine, i was wanting to ask a
quick question. I am in the final stages of my project and I am now
ready to construct the mobile interface. The design that Costas Vlachos
helped me with just needs to some clarifying, there is a zener diode in
this circuit, and i am unsure what zener to choose to perform the
correct conversion of the signal from the RX line, for the time being i
have selected the 1N4678 diode but this is just a guess.

http://groups.google.co.uk/group/sc...q=hybrid_snyper&rnum=2&hl=en#560a336845019a11

Thanks in advance

Wayne

Hi Wayne,

I had a quick look at the posts in your old thread. Are you building the
circuit in this URL?

http://www.riccibitti.com/tinyplanet/tiny_article.htm

If so, you don't actually need a Zener because of the additional
transistor, whose B-E junction won't allow the base voltage to go above
0.7V anyway. You can replace the Zener with a 1N4148 just to clip the
negative voltage from the RS-232's Tx line. Just connect the base of the
BC547 to the diode/4.7k node. The modified part of the circuit in the
above URL would then look like this (view with a fixed-width font):

.. +5V
.. |
.. |
.. 10k
.. Pin 2 |
.. of J1 o---+--- . . . +----------> To PIC Rx
.. (Tx) | |
.. | C
.. `---4.7k---+-----B BC547
.. | E
.. --- |
.. 1N4148 / \ |
.. --- |
.. | |
.. GND GND

Hope this helps.

--
Regards,
Costas
_________________________________________________
Costas Vlachos Email: [email protected]
SPAM-TRAPPED: Please remove "-X-" before replying

 

[hybrid_snyper]

Hi Wayne,

I had a quick look at the posts in your old thread. Are you building the
circuit in this URL?

http://www.riccibitti.com/tinyplanet/tiny_article.htm

If so, you don't actually need a Zener because of the additional
transistor, whose B-E junction won't allow the base voltage to go above
0.7V anyway. You can replace the Zener with a 1N4148 just to clip the
negative voltage from the RS-232's Tx line. Just connect the base of the
BC547 to the diode/4.7k node. The modified part of the circuit in the
above URL would then look like this (view with a fixed-width font):

. +5V
. |
. |
. 10k
. Pin 2 |
. of J1 o---+--- . . . +----------> To PIC Rx
. (Tx) | |
. | C
. `---4.7k---+-----B BC547
. | E
. --- |
. 1N4148 / \ |
. --- |
. | |
. GND GND

Hope this helps.

--
Regards,
Costas
_________________________________________________
Costas Vlachos Email: [email protected]
SPAM-TRAPPED: Please remove "-X-" before replying

Oh right i see, i didn't understand why the zener was there with the
addition of the transistor on the RX line. I am using the circuit in
that link with the addition of the help that was given a while back.
the difference being that I am using a PIC16F876 instead of the
ATtiny12 as used in the link.

Thank you for getting back so prompt, you have been a big help.

Wayne