Frequency division with 74192

Discussion in 'Homework Help' started by CircuitZord, May 11, 2015.

  1. CircuitZord

    Thread Starter Member

    Oct 8, 2012
    59
    2
    I am trying to implement this circuit, with a 74192 instead of a 4017 as used for IC2 in the schematic

    http://3.bp.blogspot.com/-dJJuEjiJv...600/simplest+full+bridge+inverter+circuit.png

    The 4017 and 74192 are both decade counters, but the 74192 has only 4 outputs, and the 4017 has 10 outputs.

    http://www.nxp.com/documents/data_sheet/74HC_HCT4017.pdf
    http://ee-classes.usc.edu/ee459/library/datasheets/74LS192.pdf

    What I can see is that the input frequency from the 555 timer is being counted in the 4017 and then resetting at pin 1, so following the pinout from the datasheet: Pin#: 3-2-4-7-10-1(RESET), essentially 5 outputs before a reset, I can't do this with the 74192 as it only has 4 outputs.

    I know I have wired the 74192 correctly because I can see the frequency being divided at pins 3, 2, 6, 7 of the 74192. How can I go about getting more outputs? I thought of cascading, and this is essentially the same it seems except that the CARRY OUT pin becomes the input to the next 74192, however this doesn't work.

    Any advice?
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    Unless there is additional circuitry we don't see, such as a 5 volt regulator and a circuit to pre-load the counter or decode the binary outputs, you should only see the '4192 divide by powers of two if it counts at all.

    A 74LS part needs a 5 volt power supply; 12 volts is likely to cook it. When operating from the 5 volt supply the 74LS part has a very limited output swing and is unlikely to be able to drive many MOSFETs very hard. You really need a CMOS part rated for 12 volts for this, and even then I worry your bridge burning because of poor switching on the gates of the P-channel MOSFETs (fasts on, slow off because of the resistive pull-up). Sorry about sounding pessimistic.

    I think the link below answers your question about cascading the '4192.
    https://answers.yahoo.com/question/index?qid=20100104043835AAiK0ib
     
  3. CircuitZord

    Thread Starter Member

    Oct 8, 2012
    59
    2
    Hey Dick,

    Thanks for your response. Yes, in my implementation I have a 5 volt regulator, so that's not an issue. I did think about its ability to drive the MOSFET, and I guess I was just hoping it would work without actually considering it in-depth, and now that you've brought it up, I think I better perhaps ditch this idea, because it's likely to cause trouble later on even if I did sort out the frequency division trouble.

    The cascaded part I've tried, it doesn't quite give me what I want, in fact I have no idea what exactly it's doing, but it's definitely not it!!

    Thanks again.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Answer your own questions! Look up the data sheets for each part. If you had, you would have seen that there is no way that one part can be substituted for the other without adding many other parts.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Few electronic projects work well using hope as a design tool. :rolleyes:
     
    DickCappels likes this.
  6. CircuitZord

    Thread Starter Member

    Oct 8, 2012
    59
    2
    Anyway...I managed to get it to work using another method. I got the waveform that I was expecting and it was doing quite well, and I was just trying to tidy my circuit up when it stopped working, and now I'm confused. The only things I changed was the wiring to tidy it up, all resistor values were the same.

    The output of those two pins 2 and 7 (IC2) are essentially square pulses that go high, but not simultaneously, they are shifted.

    When there's a high at the base of the BJT, the collector goes low.
    This happen for both BJT's

    My issue now is that although the signal (pulses) going into the base is correct (before the resistor), the collector output isn't right anymore :S I probed the voltage BEFORE the BJT base resistor and the signal pulses are as they should be, no distortion. The signal at the base of the BJT (after resistor) is 0V, perhaps very minor pulses, why is this?


    When I turn up the voltage, until about 5V it works as expected then the collector's go to ground. If I rapidly turn the voltage knob on and off, then it comes back up again, but the waveform is 'wavy', it's distorted. I don't understand why it's doing this. Maybe up to 12V it will work again and then shut down, if I again turn the voltage knob quickly, it will come back up again and the waveform is normal again. WHY?

    I though maybe the PSU has an issue, so I tried it with the other channel, same results. I tried it with BC547 transistors, PN100, and some other stuff, the same results.

    The collectors go to 12V with a 1kohm pull-up[​IMG] resistor, and the resistor the base of the BJT was 2.2kohms, I also tried 10kohms, no difference.

    Could someone please tell me what's going on?
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    Post your schematic ...
    - a screen shot of your work if you are using a simulator, or
    - a picture of your bradboard.
     
  8. DickCappels

    Moderator

    Aug 21, 2008
    2,664
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    Just a note: A circuit like this should have bypass capacitors on everything. Lack of sufficient bypassing can lead to trouble.
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,164
    Yet in your latest picture, you still have a 12 volt source connected to the 4017, which you stated you replaced with a 74LS192.

    Can you provide a schematic diagram annotated with the component values "as you built it"?

    I don't see how you can expect people to help you when your giving them something that doesn't reflect what you've built or are attempting to build.
     
    Last edited: May 13, 2015
  10. CircuitZord

    Thread Starter Member

    Oct 8, 2012
    59
    2
    I am sorry, you're right. I have now fixed the issue by using two HEX inverters instead of using transistors, but I'd still like to know why it went wrong the way it did.

    Here's the revised schematic I had used, instead of a 4017 counter, it basically uses two JK flip flops (CD4027) and two AND gates (CD4081), instead of the TTL version shown in the schematic I used the CMOS versions that allowed me to run it from 12V.

    Here are the datasheets for the JK flip flop and the AND gate;

    http://www.biltek.tubitak.gov.tr/gelisim/elektronik/dosyalar/3/CD4027BC.pdf
    http://www.e2v-us.com/shared/content/resources/File/documents/QP semi/NSC_CD4071BC.pdf


    [​IMG]

    The 555 is clocking at 200Hz, do not worry about the values used for the 555 in the schematic, that's not what I used, I adjusted it to get the frequency I wanted, it's a CMOS version of the 555.

    Basically, everything up to and including the outputs of the AND gates were correct, at full rail voltage (12V) I would get nice clean 0 - 12V pulses. When the transistors were connected to get the inverter output at the collectors, the expected output at the collectors weren't correct (wavy, distorted).

    Like I mentioned earlier, when I first implemented the circuit with jumper wires, it worked perfectly, when I was tidying it up by putting in new wires to tidy up everything, is when it stopped working.

    The circuit is currently working with everything unchanged up to and including the AND gates, I just replaced the transistors with a HEX inverter and I'm able to drive H-Bridge as wanted.

    Cheers
     
  11. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    And yet you failed to note on the schematic the changes. I can only assume you snatched that schematic from somewhere else and you used that as a guide, without making your own drawing. When one get's sloppy like that, they will shortcut and put the uncorrected schematic in their report and their professor (or boss) will ask them why the supply voltages so high ... assuming you get to see them before being shown the door. You need to exercise some due diligence.

    Well, the current diagram has no inverters, and you provided a partial schematic (no h-bridge), but if your happy with the results, great .... and we will never know why your original went wrong because you never provided an "as built" schematic. We can surmise IF we knew how you connected that 74LS192.

    In the future, when asking for assistance, you should provide a fully annotated schematic and photos.
     
  12. CircuitZord

    Thread Starter Member

    Oct 8, 2012
    59
    2
    I'd like to clarify that it was never my intention to pass off another design as my own, nor was I trying to hide anything. I'd like to also point out that I'm not using the 74192, that is what I was using earlier, or at least trying to. I didn't include the H-Bridge because the schematic I used online didn't have one! And also because it's not relevant at this point, my issue was simply with the collector of the transistor, whether I connected the H-Bridge or not, it makes no difference, the collector output is wrong.

    I'm unsure what my rail voltage has to do with anything ? It was 5V earlier simply because the 74192 is TTL logic, I changed it to 12V because my AND gates as well as the JK flip-flops are CMOS versions which can support higher voltages.

    The current diagram has no HEX inverter because my HEX inverters are NOT the problem. The current diagram has transistors which WERE the problem, that is what I wanted to clarify, why weren't they working? If I put my inverters in there, I'd be showing you a schematic of a working circuit, of which I have no need to troubleshoot. The last diagram is the one I'm having trouble with.

    Once again, I didn't include the H-Bridge because that is not relevant, the gate signals coming out from the transistor are wrong, thus the H-Bridge won't work properly. I was only trying to find out why my collector output voltage was distorted.

    As an aside, I have no intention of 'snatching' schematics for my professor to see, and I couldn't even if I wanted to because neither of the schematics I followed are the full implementation of what I have, I will have to make my own diagram with the changes I have made.
     
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