Please Help With LM35 to ICL7117 (post#16)

Discussion in 'The Projects Forum' started by ro169, Apr 26, 2015.

  1. ro169

    Thread Starter Member

    Oct 10, 2014
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    Hi all,

    I'm currently working on a digital thermometer. The project must be completed using non-programmable IC's!
    The part I need help with is displaying the 8 bit output of the ADC on a a pair of seven segments.

    I originally planned on using the attached circuit from:
    http://www.electro-tech-online.com/...of-adc0804-to-decimal-view-in-segment.130139/

    However I was unable to get my hands on the counters they've specified (4526). The counters/BCD's I can currently get are: 4510, 4511, 4026. Is it at all possible to make this circuit work with these IC's?

    Any/All help will be appreciated.
     
  2. MrChips

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    Oct 2, 2009
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  3. ro169

    Thread Starter Member

    Oct 10, 2014
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    I'm currently using the ADC0804 as per suggestion from the LM35 datasheet.
     
  4. MrCarlos

    Active Member

    Jan 2, 2010
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    Hola ro169

    As for what you said in your messages, all you requires is a Natural Binary to BCD 3 digits decoder.

    You can research on Google.com by the phrase written in bold.
    I did and found the attached .PDF document. Just to study and learn.
    I hope I'll be useful to You

    By the way: How you develop the image, So huge, that appears in your post #1 ??
     
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  5. ro169

    Thread Starter Member

    Oct 10, 2014
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    Thanks MrCarlos.
    Will check if I have these IC's available and build and test this circuit. The principles behind the circuit seem sound, I hope the connections are right.

    However, there are a couple of things that I do not understand on the circuit:
    1. Between IC3a and IC3b. There is an RC circuit. What is the reason for this?
    2. Are the pull down resistors on the comparator really necessary? These inputs will be from the ADC which will naturally only input either high or a low to each bit on the comparators.

    Also I don't understand what you're asking about the image from #1. could you please rephrase?
     
  6. MrCarlos

    Active Member

    Jan 2, 2010
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    Hello ro169

    1. IC3a, IC3b, C1, and R9; all of them form a circuit named One-Shot.
    As soon as the comparators 'say' A=B, In A=B output of IC2(6) shows a logic high level.
    Initially the capacitor C1 is discharged. IC3b 'Feel' a high logic level at its input,
    That high logic level triggers the one-shot circuit.
    Thus the capacitor C1 begins charging at a rate determined by the RC time constant. So IC3b 'Feel' now a low logic level. Upon reaching the threshold voltage IC3b time of one-shot will end back to its original state.

    2. Pull Down resistors that are necessary or not depends on what's connected to these inputs of the comparators. If the outputs of which is connected there are open collector type, then it would be necessary

    You said:
    Also I don't understand what you're asking about the image from #1. could you please rephrase?
    Yes, what was the software you used to do the drawing, so big, that appear in your original message ??
     
  7. ro169

    Thread Starter Member

    Oct 10, 2014
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  8. ro169

    Thread Starter Member

    Oct 10, 2014
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    The NOR gate IC output is fed to pin 6 of the 40110 [Latch Enable Pin].

    Am I right in saying that because in their circuit the clock pulse is at 5kHz which means therefore the 40110 doesn't "realize" that the latch pin is being sent a high as it lasts for a split second and that the delay created by the capacitor discharging gives it the time to do so?
     
  9. MrCarlos

    Active Member

    Jan 2, 2010
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    Hola ro169

    Well, I do not clearly understand what You say:
    Am I right in saying that because in their circuit the clock pulse is at 5kHz which means therefore the 40110 doesn't "realize" that the latch pin is being sent a high as it lasts for a split second and that the delay created by the capacitor discharging gives it the time to do so?

    But it seems that you mean that the IC 40110 will not perform the 'Latch' action.
    Note that this IC 40110 requires a negative pulse of very short duration to make its Latch action.
    The width of this pulse is determined the time constant formed by capacitor C1 and resistor R9.
    How narrow can be this negative pulse (1, 0, 1) for the IC 40110 'feel' it ??. . . well that is specified in the data sheets of 40110.

    You understand clearly what is the technique using the circuit of which we still talking?
    You could describe it in four lines. ??

    You could use for the 8-BIT Binary Decoder BCD To type ROM memories which would address your ADC0800 output and output data of the ROM would be 4, 4, 4 BIT's decoded for display BCD's.
    This is another conversion method which seems the easiest to do. But a programmer memory is required.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    MrChips suggestion in post #2 is much easier to implement as the ADC has a built-in output for a 7-segment display.
    It will interface fine to the LM35 and no complex binary to BCD conversion is required.
     
  11. ro169

    Thread Starter Member

    Oct 10, 2014
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    Hi,

    Several of the IC's required to do the 8 bit binary to BCD conversion without using programmable devices aren't available for purchase in my area.
    Will look at interfacing the ICL7106 (as suggested by Mr Chips) with the LM35.

    Are there any suitable replacements for ICL7106 that drive common cathode displays?
     
    Last edited: Apr 28, 2015
  12. MrCarlos

    Active Member

    Jan 2, 2010
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    Hello ro169
    I think it's best to look the other way. investigates electronics stores which IC's are like the ICL7106. then you look at their data sheets here: http://www.alldatasheet.com/ intended to see if it's for your project.
    I probably find one that can handle Display's of common cathode, but if you do not get it in your area ??
     
  13. crutschow

    Expert

    Mar 14, 2008
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    Why not buy a common-anode display?
     
  14. ro169

    Thread Starter Member

    Oct 10, 2014
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    Have changed to the ADC to the 7117. The ability to latch a conversion for interface purposes is desirable.
    Have also switched to common anode displays to support this ADC.

    Thanks for the Help.
     
  15. MrChips

    Moderator

    Oct 2, 2009
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  16. ro169

    Thread Starter Member

    Oct 10, 2014
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    Hi,

    I need some help with the circuit and the calibration of the ICL7117. (This is my first time working with an ADC)
    Below is the circuit I've used according to the datasheet. With a supply voltage of 5V.
    I'm not sure what to set the 10K pot to. Also there are to references to pin 29 on the diagram below. Does this refer to 2 capacitors in series?

    LM35 to ICL7117.png

    With the circuit connected as above. ALL output pins are at a high. Given that the ICL is a common anode Seven segment driver this means none of the segments light up
     
    Last edited: May 3, 2015
  17. ro169

    Thread Starter Member

    Oct 10, 2014
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    Also.
    The IN LO pin (30) should be referenced ground.
    However this isn't possible as 30 also goes to 32 which goes to 26 which goes to VCC. So connecting 30 to ground will short VCC to ground.
     
  18. MrCarlos

    Active Member

    Jan 2, 2010
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    Hello ro169

    Where did you get that circuit I look in your post #16?
    Has another error: the PIN 26 is named -V but at the end of the line says +5V.
    It will not be that between 35 and 26 PINs is a 5V power supply where the positive is connected to pin 35, and the negative to pin 26 ??.
     
  19. Dodgydave

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    Jun 22, 2012
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    Last edited: May 4, 2015
  20. ro169

    Thread Starter Member

    Oct 10, 2014
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    Hi,

    The datasheet is from the same link that Dodgydave has just posted.

    Dodgydave, the link you've posted is the same datasheet I'm using. The reason I'm using the circuit in figure 2, not figure 1 is that figure 2 is the ICL7117 whilst figure 1 is the ICL7116. I'm currently using the ICL7117 (figure 2 -- It isn't working).

    Thanks.
     
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