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Mobile to PIC TX/RX connection

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.

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Thanks in advance

Wayne

Reply to
hybrid_snyper
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Hi Wayne,

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

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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
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Costas Vlachos  Email: c-X-vlachos@hot-X-mail.com
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Reply to
Costas Vlachos

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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

Reply to
hybrid_snyper

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