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12v input to SX28 as switch. — Parallax Forums

12v input to SX28 as switch.

eagletalontimeagletalontim Posts: 1,399
edited 2009-02-22 20:53 in General Discussion
I have a quick question. I know the SX cannot handle a direct 12 volt DC connection to the pins so I was wondering if putting a 100K 1/2 watt resistor inline would be ok. I would also run another 100K from the pin to ground. If there is a better way, please let me know [noparse]:)[/noparse] The existing circuit that used to be installed from the factory has a 1K in series with the 12V and run directly to ground. Right before the resistor, there is a 4.7k that runs to the chip. I am worried about doing this with the SX since the 1k seems like it would get extremely hot.

Comments

  • JonnyMacJonnyMac Posts: 9,214
    edited 2009-02-22 20:38
    In RS-232 circuits (which can swing to ~15v) a 22K resistor is used to limit the input current to a safe level. What I prefer to do is use a voltage divider with a 10K and a 4.7K.

    12v ---[noparse][[/noparse] 10K ]---+---[noparse][[/noparse] 4.7K ]--- Ground

    With 12v on the input you'll get about 3.8 volts at the "+" -- this is safely above the 2.5v CMOS threshold if that is used (assuming Vdd = 5v).
  • eagletalontimeagletalontim Posts: 1,399
    edited 2009-02-22 20:53
    ok, thank you [noparse]:)[/noparse]
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