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???
01/29/09 06:40
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 		 #161808 - May need to have pullup resistors
Responding to: ???'s previous message
The use of the ULN2803 is very much like designing with discrete BJT devices. If the MCU pin that connects to the inputs of the ULN2803 has very weak pullup capability or is open drain with some small current leakage paths the 1.5 volts you see on the port pins will be mostly due to two the VBE drops inside the driver.



This means that the problem that you are having may not be a grounding problem at all. I suggest you try adding a 1K to 1.5K pullup to the MCU VDD on each input to the ULN2803 and see if this enables the inputs to rise up to levels you expect.

Michael Karas


List of 34 messages in thread
TopicAuthorDate
Serial Communication Problems            01/01/70 00:00      
   standards have a purpose            01/01/70 00:00      
      Serial Communication Problem            01/01/70 00:00      
         OH, how often            01/01/70 00:00      
   No negative Tx supply            01/01/70 00:00      
      Serial Communication Problem            01/01/70 00:00      
   Software or documentation bug            01/01/70 00:00      
      I am so new sorry            01/01/70 00:00      
         Reset            01/01/70 00:00      
   I found this Image at google            01/01/70 00:00      
      Read datasheets to better understand            01/01/70 00:00      
      which derivative            01/01/70 00:00      
      It will meet the RS232 requirements            01/01/70 00:00      
         Are You sure?            01/01/70 00:00      
            are you saying "PC" when you say "mother board"            01/01/70 00:00      
               You are right , Eric,            01/01/70 00:00      
                  because            01/01/70 00:00      
                     cheap is paradigm today, so            01/01/70 00:00      
                        That's odd ... I've never seen one ...            01/01/70 00:00      
                           odd, but real .            01/01/70 00:00      
                              Explaining to beginners            01/01/70 00:00      
                                 agree            01/01/70 00:00      
                           look for a copy of the EIA standard and read it            01/01/70 00:00      
                           right, but not the issue            01/01/70 00:00      
            RS-232 transceiver in PC            01/01/70 00:00      
   Basics            01/01/70 00:00      
      MAX232 vs DS275            01/01/70 00:00      
         It is not that simple            01/01/70 00:00      
            I bought the required componentss            01/01/70 00:00      
               It worked! Yahoo!!!!Googlooo!!!            01/01/70 00:00      
   Circuit Design            01/01/70 00:00      
      May need to have pullup resistors            01/01/70 00:00      
         It worked, thanks!            01/01/70 00:00      
            It destroyed though my red led            01/01/70 00:00      

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