555 timer

Thread Starter

darklord_V

Joined Sep 7, 2011
13
So now what should be my next step???i have rewired this circuit for almost three times .....what must i do now?

here is what i observed......when the counter is supposed to show 2 only the second ff Q output has to have a 1 as an output(2=10) but the led i attached to the Q output of FF1 also keeps blinking very fast
 

SgtWookie

Joined Jul 17, 2007
22,230
Do you have resistors in series with the LEDs? Say, 1k-2k resistors? If you do not, the LEDs will act as a voltage clamp, and keep the circuit from working properly.

If you changed over to all 4000 series CMOS, you will have to use 10k in series with the resistors, or else the LEDs will load the signal down too much.
 

capnray

Joined Jul 3, 2010
59
I consider the 555 a poor device, unless it is controlled by an outside source. Crystal/line AC controlled is best for any clock displaying time. If you are clocking a circuit, and don't care, use an RC with a Schmidt inverter.
 

Wendy

Joined Mar 24, 2008
23,415
The 555 does what it is supposed to, which is provide a decent signal with a minimum of parts. BTW, the crystal/4060 circuit I linked to has gained 9 seconds in three days, not bad for a circuit with no adjustments.

I assume the OPs circuit is purely simulated. The last diagram STILL didn't have the set reset inputs tied down to ground. This is not optional, and until this happens I will keep pointing out the obvious. It also distracts looking at the rest of the circuit, why waste my time elsewhere when something so obvious and so simple has not been fixed? It doesn't matter what is said, what matters is the schematic.

One other thing, I assume (dangerous that) that that counter is supposed to be a BCD (binary coded decimal). If so then 4 flip flops are required. For a hex counter you can use 3 flip flops.

The 7490 is a BCD counter, the 7492 is a hex/12 counter. Both these chips have a fully functional BCD/hex/12 counter laid out in their data sheets.

For a properly designed counter the outputs should be Q out only, no gates needed to couple to the 7448, which requires a BCD count. When I was a beginner I build quite a few of these circuits. Back then I could do it in my sleep, but that was more than 3 decades ago. The basics don't change though.
 
Last edited:

Thread Starter

darklord_V

Joined Sep 7, 2011
13
sorry for the late replies......got the time to work on it again....sorted the circuit out...now i have got a 0-5 counter and 0-9 counter......what i wanted to ask was that how do i increment the second counter when the first goes from 9 back to 0....
what i did was to connect the Q output of FF1 and FF4(9=1001) of decade counter into a AND gate , using it as the j output of the second counter.but this doesn't work because when the decade counter goes from 9 to 0 the divide by 6 counter goes to 1.......but then also increments to 3 and then 5 and then back to 0.
 

Attachments

SgtWookie

Joined Jul 17, 2007
22,230
OK, you're starting to have a bunch of wires on the schematic that you could do away with.

You really only need one voltage source; V1 or V2. Attach the Vcc node name to it. Then use that node name whereever you need that voltage instead of running wires all over.

Similar with GND. Use the GND symbol if you find yourself running long ground wires.

You still are using 12v on 74 series TTL; in the real world, that will burn up parts. You need to decide which technology you are going to use; 74 series or 4000 series parts (one or the other) and then stick with them. If you are using 74 series parts, then you must use 4.5v to 5.5v for Vcc.

As far as the counting goes - ask yourself under which conditions you need to increment or reset the count for a particular digit. Let's say your seconds digit counts up to 9; input A and input D will be high. So, the next clock that comes in, you need to send a clock to the seconds' 10's digit. You'll need something like a 3-input AND gate to pass the A, the D, and the clock inputs.
 

Thread Starter

darklord_V

Joined Sep 7, 2011
13
thank you SGT WOOKIE.....thats a brain opener.... the A and D will be inputs to the AND gate and that should be the clock(this was what i did wrong as you very well new:D) for the mod 6 counter.....
I intend to use the TTl series....setting the voltage 5v right now...
thanks again....will ask any problem thats comes up... thanks SGT
 
Top