Step circuit

Discussion in 'General Electronics Chat' started by karas, Aug 15, 2014.

  1. karas

    Thread Starter Active Member

    Sep 8, 2011
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    Hi I need to build steps circuit the circuit increase one volt each one step and the time for each step is one second,so can someone help me
    thanks
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    How many total steps?

    What happens at the last step?

    Counter driving a DAC comes to mind...
     
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  3. absf

    Senior Member

    Dec 29, 2010
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    How much current for the output of the voltages stepped and what is the MAX output voltage ? Can you use mcu or just discrete logic chips ?

    Allen
     
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  4. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Maybe not the most optimum solution but might help your thinking process.

    Use a binary counter fed by a 1 Hz clock signal and feed the counter outputs into an D/A.
     
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  5. ScottWang

    Moderator

    Aug 23, 2012
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    You might talk some more details.

    If you using the normal DAC, it could be too many steps for each step 1V, so using a binary counter and 4 bits r2r dac circuit, you also need a 1Hz oscillator as this.
     
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  6. crutschow

    Expert

    Mar 14, 2008
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    There's no reason to build a complex discrete DAC circuit. Just use a standard 8-bit DAC and toggle only the higher order bits you need to generate the required steps. For example the upper three bits could give you seven 1V steps by proper scaling of the output.

    How high do you want these one volt steps to go (what's the maximum output voltage)?
     
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  7. karas

    Thread Starter Active Member

    Sep 8, 2011
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    it is vey low current (5 milli amp) and max out put voltage is 10 v
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    For a not precisely method, using NE555, CD4017 and some 1n4148, some resistors.

    NE555(1Hz) → CD4017(counter) → 1N4148 → Voltage divider(resistors) → Vout

    1N4148 x10, 10 resistors and one common resistor for voltage divider.
     
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  9. crutschow

    Expert

    Mar 14, 2008
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    What do you want it to do after it reaches 10V, reset and start again from 0V?
     
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  10. crutschow

    Expert

    Mar 14, 2008
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    Below is the simulation of a circuit, as Scott suggested, with a 555 clock, a binary counter, and an R-2R ladder network with an op amp and transistor buffer output that gives ten 1V, 1 second steps and then repeats.

    Is that more or less what you want?

    Edit: The +12V power and ground connections to the counter and the AND gate are not shown.

    Note that for best accuracy/stability you can use two 10kΩ resistors in series to make the 20kΩ resistance values. That also simplifies the part's list, although at the expense of more parts.

    Step generator.gif
     
    Last edited: Aug 16, 2014
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  11. karas

    Thread Starter Active Member

    Sep 8, 2011
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    After reach 10 v it stays and reset and start again when I enabled again
     
  12. karas

    Thread Starter Active Member

    Sep 8, 2011
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    it works perfect , thanks so much
     
  13. karas

    Thread Starter Active Member

    Sep 8, 2011
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    what is the function of the transistor in the circuit and when Q1 is high what is vbin and vout and also when Q1and Q2 are on what is the value of vbin and vouto
     
    Last edited: Aug 17, 2014
  14. Brownout

    Well-Known Member

    Jan 10, 2012
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    The transistor provides some isolation from the load. It helps prevent changes in load current from affecting output voltage.
     
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  15. karas

    Thread Starter Active Member

    Sep 8, 2011
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    please what is the values of vbin at different steps and also vout and what is the REASON of USING the transistor
     
    Last edited: Aug 18, 2014
  16. crutschow

    Expert

    Mar 14, 2008
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    The value for Vbin is shown on the graph and is approximately .747 of the desired Vout which is why the op amp has a gain of 1.338. The Vout steps are 1V.

    What do you mean by "value of the transistor". It's shown as a 2N2222 but most small NPN transistors will work. Its purpose is to provide more output current than the op amp can supply.

    Note that the circuit I posted cycles continuously. If you need it to stop at the end and return to 0V (or stay at 10V) until a switch is actuated to repeat the cycle, then I can modify the circuit for that.
     
    Last edited: Aug 18, 2014
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  17. karas

    Thread Starter Active Member

    Sep 8, 2011
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    sorry i mean the reason of using the transistor
     
  18. crutschow

    Expert

    Mar 14, 2008
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    The transistor is a voltage follower to boost the output current since the 5mA you mentioned may be near the limit of what the op amp can deliver. But if the output load is never lower than 2kΩ you can eliminate the transistor and just connect R15 directly to the op amp output.
     
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