Decade Counter with 50% Duty Cycle Question

Discussion in 'General Electronics Chat' started by Metalfan1185, Mar 9, 2009.

  1. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    Ok, attached here are circuit_strobe_circuit.png which is the circuit i made to make some strobes.

    circuit_strobe_oscilloscope is the reading of an oscilloscope with channel A on the output of the starting 555 Timer and B on the output of the 7490 counter.


    I want the waveform on the bottom (B) to be on for 10 pulses on channel A, and then off for 10 pulses on channel A.

    What i have is on for 3, and off for about 7. I dont see where im going wrong here...any suggestions?
     
  2. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    the circuits look like crap if you just click on them, i think you may have to view them in full screen or download them and open them in paint. that is the program i copied them from.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Use the Qd output (U6 pin 11) to clock a D-type flip-flop (4013) that has it's Q\ output tied to the Data input. The Q output will then toggle every 10 clocks. Don't forget to tie the Set and Reset inputs to ground via a 10k resistor to prevent odd behavior (ALL unused CMOS INPUTS must be tied to Vdd or GND/Vss)

    By the way, Q1 and Q2 are N-channel MOSFETs. You should have their SOURCE terminals connected to ground, and the DRAIN terminals sinking current from the load.

    Connect the gates to the 555's outputs using 47 Ohm resistors to keep current (and gate oscillations) under control.
    Also, connect the gates to ground with a 10k resistor to turn off the MOSFETs in case the 555's fail or are removed from the circuit.
     
  4. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    Thanks, especially for looking over my whole circuit and not just the issue.:D


    ummm...Do you think im going about this the right way? is there another simple logic IC that can take the place of both the 7490 and the 4013 IC that you mentioned?

    Im trying for a circuit that flashes strobes at the same speed, and by making one speed adjustment, you can change the alternation speed of both lights.

    I figured rather than to set a 555 for 50% duty, use a divide by 10 counter, that way the duty cycle doesn't matter at all. By changing the frequency, you can adjust the speed of the alternations. if it was done this way i figured that the flashes would be variable alternation speed, but with a constant 50% on/off time between the two.
     
  5. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    Ok, I revised the circuit on the MOSFET side, i believe that the way i have it now is the way you explained it. Let me know if i got something wrong still.

    I did not add the 4013 yet, i may add it still, but i might build a lot of these, so im looking for an IC that may offer similar results with less parts. The board im trying to fit it on has enough space for the 7490, but not that and the 4013, so...please dont think im not taking your input, im just still lookin into it.:)


    By the way, i dont know if you remember, but this is the same circuit i asked about before the holidays about the 50% duty cycle timer and driving the other two independently...
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Do you just need a 50% duty cycle, variable frequency square wave, or are you using the counter for something else?
     
  7. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    nope. the sole purpose is to emulate the quick alternating flashes of emergency vehicles.

    im looking for a circuit that will allow me to adjust the speed of the alternations of the timers with one adjustment. say one timer has a red LED and the other a blue one, the red one would flash quickly, then the blue one would flash quickly, but only one led is on at a time.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    What duty cycle do you want your output pulses to have?
     
  9. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    well, the secondary timers duty cycle doesn't matter...well...kinda.

    im thinking a fast set of flashes like the LED Police lights on the Police cars.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    396
    If you wanted a 50 % duty from 7490 in put clock at Bin,pin 1 , output QD to A in,14, out QA is 50 % duty.
     
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    396
    Six red & blue LEDs flashing at 2:1 on-off ratio or about 126 ms on, 62 ms off for 6 times each. A spare half of 4013 available for some other flasher or ground inputs. R values just guestimates. Not breadboarded.
     
  12. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    This looks promising!

    Ii saved it in my laptop so i can simulate it later on. As for right now, i have a VW engine to rebuild.

    one question though, it seems the 4011 Power pins are connected to +12 and GND, i thought those were 5V chips? I know the 7400 series chips are.

    Im probably mistaken.


    Thanks again Bernard! Ill post up the Sim results and maybe breadboard it when i get some time in the VERY near future.
     
  13. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    Ok, here is a simulation on the circuit that you drew above.

    The simiulation runs great, but if you look at the scope, i set the top trace to (red) and the bottom trace to (blue)

    as you can see, there is a slight amount of time when both colors will be on at the same time, although this is unexpected, im wondering if this is an even closer "Police Flasher" emulation than i expected.

    There is also a slight drop back to GND in the middle (almost) of the pulse. I dont know what's causing this.


    By running this, i am favoring this unexpected outcome, but im still looking into the one light on at a time deal.

    This is so close!!!

    Thanks again!

    I wonder if this was assembled on a breadboard if it will act the same way it does on the sim.
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    396
    All ICs except 555 are CMOS , 3 to 15V VDD, 74C90 same function and pin out as TTL 7490. Circuit except for 74C90 works as expected by LED & eyeball. Will try a divide by 8 74C93 which I have ,,,, bowling & company tomorrow.
     
  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    396
    Better yet, subatituted 4022[ or 4017] for bad 74C90 with great results. Connected P5[count 6] to Deset P 15. Clock P14 now goes directly to 333 P3 as clk needs a rising edge eliminating need for A & B of 4011. 4022 output P5 now to toggle in on FF[ also was using 4027 FF because I had one].Used A & B as inverters for two LEDs , brt. white & dim red, with 2.2 kΩ current limiting resistors. No overlap or any thing strange, just 6 red blinks followed by 6 blue ones. 555 timing , .05μF, 1MμΩ, 4.7M P3 to Gnd.-to shorten off time.
     
  16. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    396
    Here is the schematic as breadboarded, still works. NAND is still 4011. Using two white LEDs.
     
  17. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    Thanks!

    Im working on getting it on a breadboard myself. I think this is it!

    thanks for all your help.
     
Loading...