Simple clock.

[rea]

Hi people, this is the first time I try make a circuit.


I have selected the 7490 for do a clock that count hours, minutes and seg.

h2h1:m2m1:s2s1

My idea is this one, have a function that detect when s2=5 and s1=9 that launch the clear and also pass a pulse to the next "phase", also when in a unit is detected X1=9 it will pass a "pulse" to X2.




I dont have for the moment the timer for pass the pulse, then Im doing it manually, ie, with unplug/plug a cable to Vcc.

I dont know if that matter.

LS90
A. BCD Decade (8421) Counter — The CP1 input must be externally
connected to the Q0 output. The CP0 input receives
the incoming count and a BCD count sequence is produced

The next is the connections that I have done: the first number is the pin, I have abreviated connected to with ->

1 -> 12
2 -> Vcc
3 -> Gnd
4
5 -> Vcc
6 -> Vcc
7 -> Vcc

8 -> LED -> Gnd
9 -> LED -> Gnd
10 -> Gnd
11 -> LED -> Gnd
12 -> LED -> Gnd
13
14 -> plugable/unplugable cable to Vcc

I think that pheraphs the problem is that I dont have a counter??? and Im using the connect/disconnect the cable in the pin 14???

If is that, I have watched an astable configuration at this place **broken link removed** and have calculated this values:

c1 = 10 micro Farads
r1 = 2K Ohm
r2 = 70K Ohm


I dont know if there exist suchs resistors is that right?

If some one can check if my connections are right? for generate a BCD count... I think that what I have in mind for pass a "pulse" to the next unit and reset then when I get 59 is what I whant, but Im unable even to generate the BCD count , some one?

 

[williB]

https://www.electro-tech-online.com/custompdfs/2005/01/DS006381.pdf
you have to connect QA ( pin 12 ) to Pin 1 to operate the way you want it to..

 

[williB]

actually you can count just by tapping the clock input to ground.
of course it will pick up every single momentary contact..
but i think your problem was not connecting QA to input B..

 

[rea]

I have it, I hae marked above in 1-> 12 but have missed to write also 12 -> 1

What about the others connections? specially the ones about reset and clear?

 

[williB]

it looks from the truth table in the pdf that if you connect all reset inputs to ground , it should count..

 

[williB]

this

 

[rea]

I put one reset to Vcc and the other reset to Gnd equal with the two Set because when I see the table of mode selection I think that I need put them like that :S


Im little confused, for example if I look at the logic diagram, then I think the only way that reset is not launched is that Mr1 and Mr2 are both 1 (because of the nand gate...¿?), but if I connect them to Vcc it dosent do nothing....


Also I correct my self above is:

7 -> Gnd not to Vcc :S


I have watched with the two resets to Gnd, aparently count, now Im realizing that my adapter is somewhat old and have a false contact somewhere... that cause some troubles, is not easy to follow.

Tomorrow I will buy a button (replace the cable) a new adapter, also dont know if the protoboard that Im using is old too? (by look I have one that look a less old) this can affect the result?


Thanks for the help and comprension . I gota sleep 0300 here or 3 a.m.

 

[Phasor]

If is that, I have watched an astable configuration at this place **broken link removed** and have calculated this values:

c1 = 10 micro Farads
r1 = 2K ohm
r2 = 70K ohm

A 555 is not nearly accurate or stable enough for a clock. You will need to use a crystal oscillator and divider.

 

[rea]

For the moment I dont need to be acurate , I only whant it to work later I will see this one about the crystal and the divider .

 

[rea]

My first eagle .


Hi here is like I have connected it now, dont know if count ok, because with the manual put of the cable it switch so fast thatt when I see 0001 (in the leds) then I see 0110 :S, I think I need buy a push button ???

By the way, here I dont put any LED, but I have connected them between Gnd and the outputs without any resistors .

I think now I dont need buy a new adapter I have solved aparently the false contact internal to the adapter putting a 10 micro Farads connecting Vcc and Gnd and there are no more cuts of power, is this correct?






I have also a extra question, now I will buy the 7 segments LEDs and the codificator/decoder? BCD to 7 segment but I dont know what to chose or what disaplays to buy Anode or Catode????

I only whant to connect the output of BCD to the display and the display to Gnd or Vcc ?? I dont whant to use intermediate gate for negate or some extra circuit , if you can help me in this place?

 

[williB]

I think I need buy a push button ???

A push botton will do the same thing because the chip is counting all the contacts that you are making ..
do you have an old PC fan lying around ?? there is a three pronged chip in there , a hall effect switch , which works nicely to test counters because when you drag the magnet past it , it switches once , nice and cleanly..

 

[rea]

No I dont have one of those :S...

About the BCD to display, what about this one:

https://www.electro-tech-online.com/custompdfs/2005/01/74LS48.pdf

And the displays will be common cathode, is that right? The porpuose is that I dont whant more circuity than the decoder to the display....

Ie, the inpu abcd = 0 and all diodes of the LED will turn on ecept one ??... ok go to buy them.

 

[williB]

i think you need common anode because the 74LS48 is active low outputs..

 

[rea]

mmm, then I still missunderstanding some things?

For example

input abcd = 0000 = LLLL
output ABCDEFG = 1111 110 = HHHH HHL

And like Understand a cathode have diodes some like the figure? then if the input is high or 1 it will conduce or emit light, isnt?

 

[williB]

I'm sorry , my mistake .. the 74LS48 has active high outputs.. sorry !!
it can supply 6 mA to drive your LED..
you are correct..

 

[rea]

Dont worry, I will try to make my timer 555 with the values that I say before and with a simple led, then if work I will continue to connect the counter directly to the bcd converter, directly to the 7 segment display, for see if can count .

If that is ok, I think I will let the less significant counter to go from 0 to 9, then my question for now is how I reset it??


In the logic diagram mr1 and mr2 are connected with a nand?

But in the logic symbol there is a and first??

And in the functional description say:

A gated AND asynchronous Master Reset (MR1 • MR2) is
provided on all counters which overrides and clocks and
resets (clears) all the flip-flops. A gated AND asynchronous
Master Set (MS1 • MS2) is provided on the LS90 which
overrides the clocks and the MR inputs and sets the outputs to
nine (HLLH).

Anyway, I will do a proof/error, but if some one whant to explain me this?

 

[rea]

Hi people, I get it to work, the timer (altough it cant turn leds on), but can clock for get the bcd count (I guess) I have passed the output to a 7448 and then to a 7 segment display and it count somewhat extrange.. lol, I will checkit, but hey, is working.. not like suposed to, but at less there are movement .


I Will chake it .

Thanks.

 

[panic mode]

what do you mean "strange"? it's not counting in sequence (it jumps randomly instead of counting smoothly?)
you might want to check the clock signal... if you are pulsing it by hand
you will see jumping. you need to debounce signal.
if you are clocking by oscillator like 555 or similar, it could be that you don't have 4bit signals wired in right sequence...

 

[rea]

Yes, by the problem related to the manual test, I decide to make first the timer.

Now Im counting with the 555 c1= 10microF r1 = 2K Ohm and r2 = 71K Ohm with "real" resistor instead of the values calculated .


I think is a problem of some false contact, I remember that in a test I see the count from 0 to 9 escept 3 that the up part isnt displayed, now it only count from 0-5 then all the led turn and and start again .




By the way, how you organize or do a circuit on a proto board?, I dont have a digital camera, but I have crossed cables elsewhere .

 

[rea]

Hi people, Im not able to get ir working in the correct secuence :S You can find the datasheet here **broken link removed** if you whant to check what I say.



I have removed the part of the 7 segment display because is more dificult follow the numbers :S....


Ok, if I put MR 1 and 2 to Vcc it is nothing in the leds (they are turn off)
if I put MS to Vcc then the number is 1001.



There are 14 pins, 2 of them are not used and 2 of them are Vcc and Gnd,

What rest are 10 pins, 2 of them are Master reset (MR) and I have connected them to the Gnd, and there are 2 that are a Master Set (MS) I also have connected them to Gnd.

4 of the 6 pins are for the ouputs and the otehr two are for the clock, I have connected C1(pin 1) to Q0 like say in the datasheet, and the C0 (pin 14) I have connected it to the outpùt of my clock.


I have disassembled it and reasembled it, only one time I remember it coun OK (the number 3 have not the top part, but was counting from o to 9), now I can register with the same circuit this diferent counts....

0, 1, 2, 5, 8, 9
1, 2, 6, 7, 8, 9

and only one time

1, 2, 7, 8, 9, 0



Some one can explain my????, I have watched only the first output Q0 and it turn on and off each aprox .5 seg, is this to fast for the internal update of the 7490??? or what Im doing wrong????

Cant understand :S.