Using a push button as start for countdown timer with 74190 ICs

I´ve been thinking for hours and just can't seem to find a way to do this. As a final project i need to make a presetteable countdown timer using 74190 ICs, i know how to preset numbers using the DATA inputs and how to connect between the 74190s, the problem is that after presetting a number i need to use a push button or a momentary action toggle to actually start the countdown. I did a diagram using a latched action instead of a push button, i would really appreciate some ideas to change the latch into a momentary action. Thank you

Your diagram shows a 7490 not a 74190, so I am not sure what it represents.

You will needs some separate device to latch the pushbutton. The 7490 or 74190 can't do that.

Im sorry, the 74190 is the one on the right but i hid the names bc they took up space. Do you have any suggestions for latching the pushbutton? Do you think i'll need to add a debounce circuit?

You will need a debounce circuit.

There are lots of ways of latching the signal from the pushbutton. A 7474 would be one way.

There is no clock source in the schematic. I'm assuming that by "countdown timer", you mean something that decrements at 1-second intervals. If so, then are you asking about an alternate-action circuit that enables and disables a 1 Hz clock into the timer with every other press?

If not, then please expand on your question.

ak

Thanks for your help, i used a 7474 to latch the momentary action. But now i have another problem and after running out of ideas and things to try i need help. The thing is that, as a down minute counter i need to modify the tens and minute counters, to block them from displaying numbers above 5, to do this i connected the Q0 and Q3 outputs to an AND gate so that when the 74190 outputs a 9 (1001) the AND gate gives a 1 and inverting that i activate the PL input from the 74190, thus letting me load a 5 every time the counter reaches 9. The problem is that for some reason, the timer doesn´t work anymore, in the picture i put a logic probe to see the logic state of the XOR output, it should work but it doesn´t, it only works when the PL input doesn´t come from the outputs of the 74190.
1 is for increments of 1.
2 is for timer start.
3 is for timer reset.