7490 counter digital clock buttons...........

so what can be done to solve this prob.....or diodes cannot work at all with button mechanism..........

See post #37 for my solution. I don't see how you can do this using diodes.

BTW, why are you using TTL logic? With CMOS it's easier to provide debounce etc delays, because smaller capacitors can be used. Also, TTL may be more expensive/difficult to source.

Hi again,


Oh yes diodes I'll take a look at some solutions like this...might be a simpler way.

Also, have we thought yet about using an actual dual one shot package? That would debounce also.


Is the end application going to use CMOS logic or TTL logic, i guess CMOS right?

Hi again,


Ok, here is a diode and single Schmitt Trigger NOR CMOS logic gate package solution. The diodes can be single or a bridge rectifier.
The button can have a capacitor/resistor for debouncing, however it must be normally low, then go high when pressed.
A good value for the two resistors is 4.7k or about that. The "CLOCK" comes from the previous stage.

Even though this circuit works with only one CMOS logic package, i think the way i would do it if i was building this would be to use a XOR gate package and also a hex inverter Schmitt Trigger package. Two ic's, but no diodes required.

hey alec i hav used your circuit but there is a problem coming that is now the count can b incremented only at 4 and 5 but not from 0 to 3..................

i hav used your circuit

Click to expand...

Which one (we have discussed various mods)? Can you post a schematic of the exact circuit you are now using, including IC types?

i hav used the ckt that you provided that cd4011 ic .......... that circuit is debouncing but now the increment can b done only in 4 and count not on 0 1 2 3 you konw what i mean to say................

hey mr al...........
can you post the schematic of this logic..........."XOR gate package and also a hex inverter Schmitt Trigger package"

The CD4011 circuit was updated in post #37 to use a CD4093 instead. You then mentioned 74LS132. So it's still not clear what you have actually done. To have any chance of finding the gremlin I need to know precisely which ICs you have and their actual pin interconnections.
Can you post a schematic of the exact circuit you are actually now using, including all IC types, component values and showing pin numbers?

seasame said:

hey mr al...........
can you post the schematic of this logic..........."XOR gate package and also a hex inverter Schmitt Trigger package"

Click to expand...

Hi,

Yes the circuit is very simple too which makes it quick to build up. I've included the debouncing part of the circuit in this drawing too.

The two IC's shown in the diagram are typical part numbers, there are other part numbers that do the same thing and also substitutes are possible. Do note however that the inverter shown there is a Schmitt Trigger inverter, not an ordinary inverter. Im not sure if an ordinary inverter would debounce properly. Also note that there are two resistors, not one, and one is much lower in value than the other one.

hey Mr al n alec my button problem is resolved..........both of you helped me alot.....many thanks..............i wanna ask 1 more thing is it possible to give a button functionality that can reset all the counters to 0.......in the schematic in post #39............thanks once again.............

Hi again,


Well, you have counters wired in two basically different arrangements:
One set has the R0 pins wired directly to ground, and the other set has their R0 pins wired to two counter outputs.

What this means is that for the ones wired directly to ground, all you have to do is disconnect one pin and connect it to a push button that has a normally low output, and when you push it it takes the signal high, thus clearing the counter to zero.

For the ones wired to the counter outputs however, you'll need to add at least one OR gate between one output and its R0 input, and connect it to that same push button.

So you have one simple wiring for the counters that have their R0 go to ground, and one slightly more complex wiring that have their R0 go to outputs. Luckily, you only need to break one of the output connections not both in order to add this functionality.

It might look a little strange to have an all zero's count being displayed if you ever intend to make this a 12 hour clock with am/pm instead of a 24 hour military time clock.

what i intend is Mr.alec.......is when the power of the clock is turned on the counters show garbage count so. i m planning to give a functionality that can reset the counters to 0 ..... and then by using button mechanism the time can be adjusted according to the need.........

Hi again,


Oh in that case you can also build a "power on reset" circuit, that automatically resets the counters to zero when the thing is plugged in.
You can do this using one CMOS inverter or whatever you have on hand that is CMOS.

if this thing is possible then can you explain how and what ic will be used and can u explain why u are using the or gate in the above circuit......u gave.....n i think cmos logic requires vdd i.e. -ve voltage .....is there a ttl version of the cmos ic that u r talking about..in power on reset ckt

Hello again,

I put the part number next to the OR gate IC right?

The OR gate is so that either the original signal from the counter OR the push button can reset the counter.
You dont need an OR gate with the counters that have all their R0 inputs going to ground, just break one from ground and use that.

I'll draw the power on reset circuit.

This diagram shows both types of counter hook ups. You dont need the push button with this circuit.