Electronics Electronic Gurus, I Need your help. Macroman, Linear? ANYONE?

Im trying to build a circuit that will allow me to use a regular SPST Momentary switch like a regular switch

this is basically how I have everything wired up



But I cant seem to get it to work, I have to keep pressing the switch and sometimes the CCFLs will flash but they wont stay on, I can get the circuit to latch but I need to hit the button a few times really fast.

 

Wow, that's a lot of circuitry.

I have a suspicion this was designed by committee over at another forum...

/me looks up your ICs...
74125 is a "Quad 3-state noninverting buffer with active low enables. "
74175 is a "4-bit D flip-flop with complementary outputs and reset. "

I get the general sense that you're trying to use the D flipflop as a T flip flop, I see a complementary output wired back to input, that's the general idea of that, so far so good. I'm a little worried you haven't pulled the reset high--it should float high but it's better design not to assume that it will.

The buffer you appear to be using maybe as a debouncer for the switch (??) but you have an input connection where you want an output and vice versa.

Let's back up a stage or two here.

The D flipflop trick is fundamentally ok for what you want to do--let's try to make that work. Back this down to just the D flip flop. I see you have all the unused inputs grounded, that's ok. Try pulling that RESET' (pin 1) high through a 1k resistor or so.

First step is, let's stick an LED on the 1Q output and watch what happens when you short CLK to ground (closing your switch). I would expect to see toggling at that stage, the LED should alternate states as you switch. Now the clock is a rising edge trigger, so it shouldn't toggle until you release the switch (i.e. CLK goes from low to high).

Try that out, if you don't get joy try to describe what happens and we'll go from there. If you do get joy, add the transistor back in, use the LED for the load, and retest. Once you're convinced that works, pop the relay in and hope for the best.

I see you're just switching a CCFL, I'd be pretty strongly tempted to eliminate the relay and go with a TIP31A transistor, switching the load directly from that.

HTH

 

That's what I figured....



It's basically what he has save the relay and (unneeded?) buffer. I swear this is like the....fourth time in a month that I've posted this schematic, but oh well.

 

Ok, I put the 1k resistor on pin1 and I hooked up an LED to pin 2 and the led goes off when I hit the switch, then when I release the switch it goes back on.

I was using the buffer for a debounce because someone else suggested that I may need to debounce the switch.


And im using this circuit to control a dual cold cathode inverter.

 

ok, I misread your post Linear and when I hooked up the led to the Q1 pin and hit the button, nothing happend.

 

Well I figure Ill give you circuit a try, but I dont have that transistor that Linear mentioned.
and what is that "symbol" on the top, that goes from ground to +5v.

and the INPUT goes to the ccfl inverter, right?

 

If you aren't seeing a transition at Q1, you either don't have the IC connected correctly, or you are misreading the pins, or the IC is broken. We have to troubleshoot that before you attach the output stage to this.

Code:

74175
4-bit D flip-flop with complementary outputs and reset. 
     +---+--+---+            +----+---+---*---+---+
/RST |1  +--+ 16| VCC        |/RST|CLK| D | Q |/Q |
  Q1 |2       15| Q4         +====+===+===*===+===+
 /Q1 |3       14| /Q4        |  0 | X | X | 0 | 1 |
  D1 |4   74  13| D4         |  1 | / | 0 | 0 | 1 |
  D2 |5  175  12| D3         |  1 | / | 1 | 1 | 0 |
 /Q2 |6       11| /Q3        |  1 |!/ | X | - | - |
  Q2 |7       10| Q3         +----+---+---*---+---+
 GND |8        9| CLK
     +----------+

Taking the rest of your questions out of order, but in order of relevance perhaps:

The orpahned connection shown on Mu's diagram is the power connection for the IC. Verify that you have pin 16 to +5V, and pin 8 to gnd, and verify that you are reading the pin numbers correctly as depicted above--8 and 16 are in opposite corners.

Verify that you've pulled the RESET' (pin 1) high.

Where Mu has 'input' that would be the positive voltage supplied to the inverter.

Let's not worry about the output stage until you get the flipflop working, but anlmost any transistor that can handle the current drawn by the CCFL invertor will work--since your toggling on/off, even the polarity isn't important.

 

FWIW, I wouoldn't use a D flipflop if I were designing this from scratch. I'd use a J/K master-slave flipflop such as a 7476--convert it to t T flipflop by tying J and K inputs together. Switch debouncing is free because of the master-slave arrangement.

 

ok, does Radio Shack even carry a T Type Flip-FLop

Code:

The pinout is more like this



      +---------------+
  /MR-|               |-Vcc
   Q0-|               |-Q3
  /Q0-|               |-/Q3
   D0-|               |-D32
   D1-|               |-D2
  /Q1-|               |-/Q2
   Q1-|               |-Q2
  GND-|               |-CP
      +---------------+

 

Um, no, you get a J/K and wire it as a T.

Go ahead and use the IC you have though. If you can't get section 1 to work, let's try it with #2 etc.

 

see my post above your last one

 

Those are effectively the same. They start counting at 0 instead of one, that's all.

 

ok, lets start from the beginning

pin 1(/MR) goes to 1k Resistor then to +5v
pin 16(Vcc) goes to +5v

pin 7 (Q1) Goes to the + of LED
pin 8(GND) goes to ground
pin 9(CP) goes to the switch which in turn goes to ground
pin 5(D1) Goes to ground
pin 12(D2) goes to ground
pin 13(D3) goes to ground


It would really help if I could get some sort of schematic with what your suggesting

 

Debouncing has never been an issue for me. Besides, I've never seen the bounce go about the switching voltage so the chip never sees anything other than a high to low transition.

 

Could you explain your schematic some more musirPmeaT

 

also, if this helps any of you heres the pinout for the buffer


[/code]
+----------+
/1OE| +--+ |Vcc
1A| |/4OE
1Y| |4A
/2OE| |4Y
2A| |/3OE
2Y| |3A
GND| |3Y
+----------+
[/code]

I had the /1OE to ground
i had the 1Y to the clock on the flip flop

 

The symbol is merely the power connection for the chip. Unfortunately the pin numbers aren't readable (vcc is 14 and gnd is 7).

I'll assume you were wanting the explaining on the "symbol" because other than the relay and buffer, it's the same as your circuit.

As far as the transistor goes any should do as long as it can handle 12 volts (which isn't a problem for the majority) and whatever current a CCFL takes.

 

and youve tested this circuit and have gotten it to work successfully?

 

I'm just suggesting we build the fliplop only section of your schematic. The LED is for debugging.

/Q1 (the complement of Q1) should also be wired to D1--that's pin 5 to 6 (not ground) in your numbering plan. This feedback is what accomplishes the toggling of states by the way.

Grounding your unused inputs (D0, D2, D3, or pins 2, 10, and 15) is a good idea, but not really crucial to operation. D1 is the input we're using though--don't ground it.

 

I built this and eightyseven variations of it, yep.

You've just got some connection issues with the flipflop, once we get through the woods on that, you'll be smiling. The rest is quite vanilla, we're not doing anything very esoteric here.