High to cmos voltage level converter

Discussion in 'Embedded Systems and Microcontrollers' started by sanjeevnaik, Jul 9, 2009.

  1. sanjeevnaik

    Thread Starter New Member

    Jul 9, 2009
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    Hi im using atmel arm7 mcu. Im interfacing external word with high voltage level.i need to convert 15v to 24v to logic 1 state in mcu and 0v to 5v to logic 0 level in mcu. Please help which ic is sutable for this level translator.or tell me other method
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    I don't know such an IC because I haven't needed one yet. However, you can use two transistors, two zener diodes and a few resistors to convert these voltage levels to appropriate voltage levels for the ARM.
     
  3. sanjeevnaik

    Thread Starter New Member

    Jul 9, 2009
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    Thanks . Please help how to do that or if any circuit diagrm please post me
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    What is the frequency of the signal?

    If it is in the range of kHz it would be better to use comparator ICs to perform this.
     
  5. sanjeevnaik

    Thread Starter New Member

    Jul 9, 2009
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    Dc voltage
     
  6. sanjeevnaik

    Thread Starter New Member

    Jul 9, 2009
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    Its digital input line
     
  7. mik3

    Senior Member

    Feb 4, 2008
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    It is a DC voltage but it varies between 0V and 24V, doesn't it?
     
  8. sanjeevnaik

    Thread Starter New Member

    Jul 9, 2009
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    Yes . I have 20 digital input it is varing from 0 to 24v so i need to convert 0 to 5v to logic 0 and minimum 15v to logic 1
     
  9. mik3

    Senior Member

    Feb 4, 2008
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    Why do you need this voltages ranges?

    You can just use a transistor with a 1K resistor on its base. When the voltage is less than 0.7V it will output a logic 1 (5V because the collector will be connected to 5V via a resistor). When the input will be greater than 0.7V the transistor will output 0V. If you want to invert the logic levels add another transistor on the output of the first to make an inverter.
     
  10. sanjeevnaik

    Thread Starter New Member

    Jul 9, 2009
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    If im using comparator circuit becom larger.no other solution
     
  11. mik3

    Senior Member

    Feb 4, 2008
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    What do you mean?
     
  12. sanjeevnaik

    Thread Starter New Member

    Jul 9, 2009
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    Any ic which do the 24v to ttl downconvertor
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    If your TTL/CMOS inputs are Schmitt-trigger, you can do it with just a couple of resistors.

    If they are not Schmitt-trigger inputs, you could use a CMOS 4093 or 74HC14 to "square up" the input signal.

    With a Schmitt trigger input, the ambiguous "in-between" voltage range is removed. For CMOS, the trigger levels are 1/3 Vdd and 2/3 Vdd. Once a trigger level is reached, the output changes states. The output stays in that state until the other trigger level is reached.

    See the attached.
     
    Last edited: Jul 11, 2009
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