Please give some hint.. Do i need to focus only in 74ls90?? nothing more? the changes are only in 74ls90?

 

Did you design the circuit you posted or was it given to you by your professor? If he gave it to you, was the instruction given to modify it so it would only count to 8 and then clear to zero?

 

QA and CLKB must connect for the loop..?

This is from the datasheet:

 

Please give some hint.. Do i need to focus only in 74ls90?? nothing more? the changes are only in 74ls90?

The decoder is not connected correctly, and neither is the display. Start by answering all of the questions I asked in my earlier post.

 

so CKB must really connect at A...

 

so CKB must really connect at A...

Yes, as stated in the datasheet. This counter will count in BCD mode and in bi-quinary, which will give a divide by 10 square wave (which isn't what you want).

 

Did you design the circuit you posted or was it given to you by your professor? If he gave it to you, was the instruction given to modify it so it would only count to 8 and then clear to zero?

no... its from me.. i just copied the normal 7-segment that count 0-9. And yes, I was planning to modify it through this one so it would only count to 8 and then clear to zero..

 

Have you read the datasheet?

not yet... O.O

Ha! You make me laugh so hard. This is a dream of yours? I've never heard of anyone talking about their dream while they are still sleeping!

Read the datasheet immediately!

 

What is the counter doing as wired?
- what counter? the 74ls90?

What were you told to do with unused inputs?
- i connect it on the ground.

What purpose does the 220 ohm resistor serve?
- to resist the power voltage..?

Will the BCD to seven segment decoder work as you have it wired?
- i thought it just connected that way...
The bubbles on the outputs of the decoder indicate the outputs are low active. You have the common terminal on the display connected to ground. Do you think that will work?

What were you taught about current limiting for LEDs?

 

Does this give you any ideas how to reset the counter to zero?

 

If you will TRY to answer the questions that I asked in post #7, we MAY be able to provide more guidance.

 

Ha! You make me laugh so hard. This is a dream of yours? I've never heard of anyone talking about their dream while they are still sleeping!

Read the datasheet immediately!

Thats what i currently doing!~

 

Does this give you any ideas how to reset the counter to zero?
View attachment 100080

what does H, L and X means?

 

What is the counter doing as wired?
- what counter? the 74ls90?

That's the only counter chip in the circuit...

What were you told to do with unused inputs?
- i connect it on the ground.

Why did you leave one of the R0 inputs floating? What logic level is TTL at with a floating input?

What purpose does the 220 ohm resistor serve?
- to resist the power voltage..?

Why did you use a resistor for one R0 input, but tie both R9 inputs directly to ground?

Will the BCD to seven segment decoder work as you have it wired?
- i thought it just connected that way...

What will wiring LT#, RBI#, and BI/RBO# to ground do to the decoder?

 

what does H, L and X means?

H = logic HIGH
L = logic LOW
X = don't care

 

How would YOU know when the counter got to nine? What device can you think of that could generate a positive signal when it recognized nine?
What pin(s) of the 74ls90 could you use to force the count back to zero? If you answer these, you have it made.

How would YOU know when the counter got to nine?
- when Q0 and Q3 is off(0).

What device can you think of that could generate a positive signal when it recognized nine?
-
- The CKB....?

What pin(s) of the 74ls90 could you use to force the count back to zero?
- Currently figuring it... >o<

 

I was mistaken. I thought the decoder control signals were tied to ground. That must be your logic supply, but in that orientation it looks like a ground.

What were you taught about limiting LED current? The decoder probably can't damage the display, but the display could damage the decoder by exceeding it's maximum power dissipation.

 

How would YOU know when the counter got to nine?
- when Q0 and Q3 is off(0).

What device can you think of that could generate a positive signal when it recognized nine?
- View attachment 100081
- The CKB....?

What logic (gate) do you need to use to decode 9?

 

That's the only counter chip in the circuit...
Why did you leave one of the R0 inputs floating? What logic level is TTL at with a floating input?
Why did you use a resistor for one R0 input, but tie both R9 inputs directly to ground?
What will wiring LT#, RBI#, and BI/RBO# to ground do to the decoder?

- ahh the 7 segment!! sorry..

- i forgot to connect it in the ground.. >o<

- shout i connect R(9) in input?

- to show the output... because when i put it in power. the counter wont make an output..

 

Look at the guts of the 7490, then see if your answers make sense...