Problem With Flip-flop and hacked clock

Discussion in 'General Electronics Chat' started by kurtruk, Jun 15, 2013.

  1. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    I have taken apart a clock and have managed to get two 2Hz outputs. However when I feed one of them to the flip-flop to get 1 Hz the flip-flop does not recognize it. It is a LG 4013. I am thinking that maybe it is the that the pulse is too short, but it is visible when connected to a LED.

    I realize that I could just use two diodes to get 1Hz, but I do not have two diodes, and I want to know why this setup does not work.

    I have attached a schematic of my circuit.

    Any answers/speculations would be helpful.

    Thank YOU.
     
  2. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    Is the ground for the FF the same as for the clock?
     
  3. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    Yes. It is the same GND for both.
     
  4. LDC3

    Active Member

    Apr 27, 2013
    920
    160
    The trigger level for the 4013 is about 70% of the voltage supply. Since the voltage to the clock is half of the 4013, the signal never reaches the trigger level of the 4013.
     
  5. JohnInTX

    Moderator

    Jun 26, 2012
    2,348
    1,029
    Is the 2ed output of the timebase really grounded? If so, it should be open.

    Is the voltage divider shown powering the timebase at 1/2 Vdd? If so, you may not be getting a valid logic high to clock the f/f.

    Other than that it should work.

    Don't forget to strap the unused CMOS f/f inputs to Vdd or GND.
     
  6. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    I tried using a transistor as a switch to raise the voltage but that did not work. More unes inputs are tied to GND.
    When using the transitor and attaching a LED to its output it even les detectable then without the transitor which doesn't make sense. C is tied to VDD E goes to the 4513 and B comes from the 2 Hz signal. Is this right?
    I don't know why it does not work.
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    The hacked desk/wall clocks don't have 2Hz outputs. They have two 0.5Hz outputs 180° out of phase. If you diode-OR them you get a 1Hz, narrow pulse output. I've used the attached circuit. Added the transistor drive to bring it up to 5V.

    Ken
     
    Last edited: Jun 16, 2013
  8. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    Ok I will definitly try your schematic, but I would like to understand it more.

    What is the purpose of D1, D2, and C1?

    I also dont quite understand the final ouput. How would it work on the collector side of the transistor?

    P.S. I really like your signature quote, even though to put it lightly I am not a fan of Edison.
     
  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    R1, D1, D2, and C1 form a simple shunt regulator to take the 5V down to ~1.5V to power the clock. Forward biased D1 and D2 act like a 1.5V Zener. C1 is used to maintain the 1.5V level high enough when the clock outputs it's brief pulses. It also filters any noise that may be present on the 5V supply lines.

    The transistor is used as a common emitter, inverting, level shifter. The voltage at the collector is +5VDC between pulses, and drops to ~0V during the pulse as shown in the schematic. You can connect the output, the collector/R3 junction, directly to your CMOS logic's input. R3 pulls the CMOS's input high and Q1 pulls the input low.

    Ken

    D
     
  10. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    Well I tried your schematic somewhat, I did not have the diodes. I got a inverte .5Hz output. Is there a way I can make it 1Hz with a dual flip-flop?
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    Yes you could do that, but it would be a lot more compact with the two diodes. The diodes are low Vforward Schottky diodes. You might try standard signal diodes like 1N4148's or the like. I chose the Schottkys because they would drop less voltage from the clock pulses...and I had them. ;)

    Ken
     
  12. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    How would I do it with the dual flip flop?
     
  13. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    You can't make a 1HZ signal from a 0.5Hz clock. A bistable would give you a 02.5Hz output.

    Ken
     
    Last edited: Jun 18, 2013
  14. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    Don't mean to be rude, but I am really confused.
     
  15. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    I was wrong!!! Sorry. Sometimes I don't have the time to think. Often I respond between times that I have other responsibilities. :(
    Also, i meant 0.25Hz not 02.5Hz
    Ken.
     
  16. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    Its tottaly fine. It can get confusing between >0 Hz and <0 Hz.
     
  17. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    I built the schematic on a perfboard, tested it on a breadboard and it worked. Put it on my clok didn't work. Tried testing it with the breadboard did not work. Tested the outputs of the hacked clock, nothing. Arrrrgggghhhh.
     
  18. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    What do you mean by "didn't work"? How about posting a schematic of your clock.

    Ken
     
  19. kurtruk

    Thread Starter Member

    Aug 26, 2012
    140
    6
    The output was coninually low. The schematic is posted a several posts above. It seems like someone would have made a simple chip that you supply with power and it pus out a 1Hz signal.
     
  20. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    I meant the circuit you are driving with my 1Hz clock circuit.

    "It seems like someone would have made a simple chip that you supply with power and it pus out a 1Hz signal. "
    No market. Many great chips have gone that way."

    No Market!


    Ken
     
    Last edited: Jun 27, 2013
Loading...