Simple clock.

i am not understanding what you want to do?
do you want to count 0 to 9 ?
or something other?

Yes, I whant to count from 0 to 9 with the 7490, but aparently I cant...

i dont understand the problem you are having?

Hi, thanks.

Im sure I have connected it for produce the BCD count, here is the draw and Im sure I have connected all in that way at the stage that I already have in memory the pins connections...


Now the timer is in asstable mode, I take the diagam from here **broken link removed** , I setup C1 = 10uF, R1= 2K R2= 71K

Time High = 0.693 * 10uF * 71K = 0.49203
Time Low = 0.693 * 10uF * (71K+2K) = 0.693 * 10uF * (73K) = 0.50589

That is the output of the timer that I pass to pin 14 or C0.




Im reading some like the minimung frequency and I guess there is where my problem are??????

There is a minimun of 32MHz for CP0 and 16 Mhz for CP1 ..... havent taked this in care... :S... is that the source of the problem????, I have watched a clock in internet that use this 7490...

What you think???

as i suspected that data sheet is incorrect..there is no minimum.. this is from National semiconductor data sheet..
https://www.electro-tech-online.com/custompdfs/2005/01/DS006381-1.pdf

I see is like the minimun for the max frequency....

Then for what it cant count, the model I have a "f" above the number DM74ls90N, the only requisite for count in BCD is connect Q0 to the pin 1 :S, then I dont understand, some times when I reset (change the cable manually of the reset to Vcc and then to Gnd or only disconnect it from Gnd) I cant get it to count 0, 1, 2 , 7, 8, 9.

Where are 3, 4, 5 and 6 ???? :S I dont understand . Or Im to noob for electronics??? :S

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

Its alive!!!!!!!


By the way, havent changed any connections (I remember that I disasemble and assemble it more than one time and much checking in the connections :S).

Remember that I say have old adapter and that have power ups and down, I have solucionated that connecting a capacitor of about 10 uF to Vcc and Gnd (by a sugestion of my brother).

After see that some times that old adapter even turn on and I need to move it for turn on, I decide to buy a new one (12, 9, 7.5, 6, 4.5, 3 I have measured directly when is at 3 and the multimeter say 5.5V ), anyway now come to mind what will happend if I connect the same capacitor to this new adapter, to Vcc and Gnd and tada is working!!!!!


Hahahaha, exactly dont understand for what is now working, but the capacitor if I remember correctly hold Volts then I need more Volts for this circuit or is only I need them more continuos???

Now is time to continue to the next part

good for you !!

or is only I need them more continuos???

Click to expand...

this is probably the reason..
dont go much more than 5.5 V , you are at the upper limit , of the allowable voltage for the chip..
is it possible to use batteries ?

That is the problem of the new adapter :S, it say 3V in the text, but its 5.5V, pehraphs I will make a Voltage divisor, also I will put the capacitor for have a more stable input .

Yes, is posible use batteryes, but I need buy them and the get carrier for make it more easy I guess .


By the way, if I make the voltage division, how many Volts will be OK? 5V? for example the ne555 say from 4.5 to 16.

a voltage divider is a good idea , but you may find that it does not work as planned.. .. ie use it just for the 7490 , let the Leds and the 555 run off the 5.5 V supply..

A 5v regulator is cheap insurance