I need help. Our requirements is to make our 7 segment display count up and down, we have a circuit but it only counts up, how can we modify it to count down? All answers will be highly appreciated.

 

The easiest is to use an up/down counter such as a 74190.

 

Welcome to AAC!

All answers will be highly appreciated.

Is this homework? Even if it isn't, most members draw the line at doing more work then the requester.

Are there any restrictions on the components you can use to implement this circuit?

 

Invert output of U3.

 

Invert output of U3.

??

 

Welcome to AAC!

Is this homework? Even if it isn't, most members draw the line at doing more work then the requester.

Are there any restrictions on the components you can use to implement this circuit?

There are restrictions with the components. We need to use those components

 

??

Thankyou!

 

There are restrictions with the components. We need to use those components

I'd say it would be difficult with an up counter with preset capability, and impossible with 7490.

Since it isn't very educational to assign problems that can't be solved for school work, there must be something you've misunderstood.

 

The easiest is to use an up/down counter such as a 74190.

Most of my classmates did that but my professor isn't satisfied. He said we should modify our circuit and not change components.

 

I'd say it would be difficult with an up counter with preset capability, and impossible with 7490.

Since it isn't very educational to assign problems that can't be solved for school work, there must be something you've misunderstood.

Is it really impossible? He said we can modify our circuit, and use inverter or add more logic gates.

 

Hi

Use inverters to invert the output of U2. The counter will still count up but the display will count down.

eT

 

Hi

Use inverters to invert the output of U2. The counter will still count up but the display will count down.

eT

We'll try that. Thankyou!

 

We'll try that. Thankyou!

Think about this before you run off half cocked. You have a BCD up counter.

What do you get when you invert 0000? Is that a valid BCD digit? What do you get when you invert 0001?

 

Here's a table of the up and down binary numbers and decimal equivalents.
I see no obvious way, other than a lookup table in ROM, to change the up count to an equivalent down count.

 

Here's a table of the up and down binary numbers and decimal equivalents.
I see no obvious way, other than a lookup table in ROM, to change the up count to an equivalent down count.

View attachment 145122

Thankyou!

 

Think about this before you run off half cocked. You have a BCD up counter.

What do you get when you invert 0000? Is that a valid BCD digit? What do you get when you invert 0001?

Yes...if U2 were a binary counter, you could simply invert all outputs. But its a BCD counter.
Looking at the truth table, you might be able control the up/dn count displayed by controlling the Q3 output of U2.