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Synchronous Transmission at +12V — Parallax Forums

Synchronous Transmission at +12V

Dan in VanDan in Van Posts: 2
edited 2006-03-29 14:04 in BASIC Stamp
Trying to take Serial·and Clock data and decode it with a BSII.· The Synchronous Data in question is a 12V source and from what I've read, will damage the BSII if connected directly from the source.

The Max232 does not support data voltage "translation" and I'm trying to·interpret the data effectively with lookup tables·once it·has an effective data voltage of +5V.

There has to be an easy fix here - I·can't see it Yet.· Can anyone help.

Thanks.

Dan.·

Comments

  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-03-29 08:45
    What do you mean by a 12volt source. Just +12v or +12 to -12volts.

    The Max232 is specifically designed to provide for the +12/-12 volt configuration.
    You may have misread something.

    Since you have 4 channels, you could use the 2 unused channels to provide for a clock bi-directionally.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-03-29 09:30
    Dan -

    I have to ask - what or which synchronous serial device produces a 12 volt output? Many asynchronous serial devices will output +12 V to -12 V as noted, but synchronous serial devices are usually limited to 5.5 V or lower.

    Regards,

    Bruce Bates

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  • allanlane5allanlane5 Posts: 3,815
    edited 2006-03-29 13:37
    Actually, if you put a 22 Kohm resistor in series with the PIC pin, you CAN then connect the other end of that resistor to a 12-volt signal. The PIC chip on the BS2 has 'voltage limiting diodes' on each I/O pin. If you limit the current those diodes have to deal with (by using the 22 Kohm resistor) then this works well. What the I/O pin sees is a 'clipped' (to 0 and 5 volts) version of your 12-volt signal.

    The BS2 can recieve RS-232 throuth a 22-Kohm resistor in the same way, actually.

    Now, DRIVING such a signal requires a few more components.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-03-29 14:04
    I believe that you can do the same 22 Kohm resistors with all BasicStamps [noparse][[/noparse]PIC or SX], but you have inverted TTL voltages swinging from 0 to V+, there are no negative portions.

    Also, you cannot generate more voltage than you have. So the 22Kohm resistor is great for the BasicStamp to receive, but doesn't help and may actually significantly worsen the transmit signal.

    If you need the swing to be inverted and from V- to V+; then the MAX232 is just fine.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
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