latch, toggle circuit

Here is how to drive an LED. If you need help in choosing the resistors, come back with an LED part number, or the LED's current rating and forward voltage at that current.

hi yes , there must be somethinng differnt with this chip?
i bought a few and they all act the same , no worries i shall use the ne555

: )

hi roff , i didn't use a tansistor, i just used a resistor and led, maybe that was it? i shall set it back up.

I told you in post #8 that you needed to use a transistor to drive an LED. If you really want help, you have to pay attention!
CD4000 series devices can't drive more than a few milliamps and still maintain valid logic levels. Since the /Q output feeds back to the D input on the 4013, excessive loading on that output will cause malfunctioning.
If you give up and go back to the 555, you are passing up a good learning experience in exchange for expediency. The 555 is a Rube Goldberg solution to your problem.

i just tried the led with a transistor , still no luck.

are you saying that the q output going back into the D input needs a transistor also? because it too is having loading issues?

what is wrong with a 555 approach?

harps said:

i just tried the led with a transistor , still no luck.

are you saying that the q output going back into the D input needs a transistor also? because it too is having loading issues?

what is wrong with a 555 approach?

Click to expand...

Earlier you mentioned the above. This lends one to believe you are directly driving LEDs with both outputs. The /Q output should drive the D input and only the D input, That is I believe what Ron was getting at when he mentioned:

I told you in post #8 that you needed to use a transistor to drive an LED. If you really want help, you have to pay attention!
CD4000 series devices can't drive more than a few milliamps and still maintain valid logic levels. Since the /Q output feeds back to the D input on the 4013, excessive loading on that output will cause malfunctioning.
If you give up and go back to the 555, you are passing up a good learning experience in exchange for expediency. The 555 is a Rube Goldberg solution to your problem.

Click to expand...

You can't hang a LED on that output. You use the Q output to drive a transistor to act as a switch. The /Q output directly drives the D input.

Someone designing a latch circuit would not use a 555 for exactly the reason Ron mentions, it is a lousy design and Rube Goldberg affair.

If you want to directly drive a LED then you would use a chip like a 7474 D Flip Flop.

Ron

harps said:

i just tried the led with a transistor , still no luck.

are you saying that the q output going back into the D input needs a transistor also? because it too is having loading issues?

what is wrong with a 555 approach?

Click to expand...

If you are feeding Q back to D, that could be the cause of your problems. You need to feed Qnot back to the D input. Qnot is the Q with the bar over it.
As Reloadron said, you would be better off not trying to drive an LED off the Qnot output, even with a transistor, until you get more experience.

i finally got it working, i nearly gave up lol.: P

i tried all the ideas , but had all sorts of weird problems due to taking out the 10k from the clock input.
As one problem i found was that going near the clock input wire with my finger made it very unpredictable i didnt realise at first.
: it seems the 10k stoped the clock input from, i think the term might be 'floating'? A pull down resistor maybe? not sure, but it stoped it acting strange.

and yes also a micro controller works much better than a switch. or touching wires.

at the moment i am using an opto isolator to take the - + from the multiplexer and then from there to the flipflop , then to a transitior to the LED. and its working great. A multiplexer controlling a latch

i beleieve also from the PDF. the flip flop uses allot less current when not in use . compared to the 555.
maybe that is one reason why you guys find it a better solution?

thanks again for your help. : )