# 0 to 9, 9 to 0 counter

#### Persian3301

Joined Nov 23, 2020
7
Hi there, got a serious problem about Counters.
i have to create "a circuit that counts from 0 to 9 then from 9 to 0 using two separate counters" and "must consider BUS concept". i used two 74192 and two 74153 Multiplexers ( for BUS ), one of the counters is ascending and another one is descending.
i think i need some kind of SWITCH between these counters at the right time. so i did some works with those A and B pins on multiplexers, tried a few things:
* make it automatic using CLOCK (played with freq and period numbers).
* tried TRIBUFFER.
** those 2 Logicstates down there should be automatic.
** 4 inputs for second counter are also for testing.
*** (as i said in the picture 9=>9=>8 or 9=>8 doesnt matter)

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#### ericgibbs

Joined Jan 29, 2010
18,011
hi P3301,
Welcome to AAC.
Are you saying that when the UP counter reaches a Count of '9', that a Bus transfer has to happen to Load the DOWN counter with '9', then the down counter counts to zero.?
E

Update:
The circuit you have posted does not use the Bus concept.

#### Persian3301

Joined Nov 23, 2020
7
hi P3301,
Welcome to AAC.
Are you saying that when the UP counter reaches a Count of '9', that a Bus transfer has to happen to Load the DOWN counter with '9', then the down counter counts to zero.?
E

Update:
The circuit you have posted does not use the Bus concept.
Thank you!
exactly, 9 to 0 then 0 to 9 and again..
oh so what should i do? ( i moved to from 74192 to 74193 and both multiplexers to one 74157, seems better now, 92 start point and reset point was a little confusing)

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#### ericgibbs

Joined Jan 29, 2010
18,011
hi P,
As this is homework I can only give you hints.
Look over this rough draft idea.
Complete the circuit and repost.

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#### Persian3301

Joined Nov 23, 2020
7
hi P,
As this is homework I can only give you hints.
Look over this rough draft idea.
Complete the circuit and repost.

E
i'm trying to complete it but the lower 74192 doesn't even count! it doesn't have any clock..
update: so i added a Clock to lower one, now both count in the opposite order to each other, but still the main problem is Switching from one counter to another.

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#### ericgibbs

Joined Jan 29, 2010
18,011
hi,
You have to use logic gates to detect when the Up counter has reached a count of 9, then select the 157 IC.
E

#### MrChips

Joined Oct 2, 2009
29,219
I see two problems on the 74157 multiplexer.

Inputs 1A, 2A, 3A, 4A should be wired to counter A.
Inputs 1B, 2B, 3B, 4B should be wired to counter B.

Pin-1 is your A/B input select.

#### ericgibbs

Joined Jan 29, 2010
18,011
hi,
It does not matter which way the 1A and 1B are used, providing the correct Select is set on the 74HC157.
E

#### Persian3301

Joined Nov 23, 2020
7
hi,
It does not matter which way the 1A and 1B are used, providing the correct Select is set on the 74HC157.
E
ok i changed those A and B wires it seems the 7seg is showing the currect number now, i made that detect circuit still nothing. only for 1 second it switches to second counter and returns to first one, needs be on Descending IC for like 9-10 pulses :C
Is there anything that do this job in Proteus??

#### MrChips

Joined Oct 2, 2009
29,219
You need a flip-flop to implement "something" to hold the state of A/B select.

I would not consider a multiplexer to be implementation of a "bus concept".
You need a counter with output enable pin.

#### Persian3301

Joined Nov 23, 2020
7
thank you guys.

#### ericgibbs

Joined Jan 29, 2010
18,011
hi P3301,
Note that on the 9th clock pulse into 74HC192, the TC/Up output pin goes Low and if not clocked again, remains Low.
Consider using that output to control the HC157 Select pin and the Up/Dwn clock control logic.
E

#### Persian3301

Joined Nov 23, 2020
7
solved it! by adding another counter, its clock is first counter's TCU and used its lowest value output to make that "something".

#### ericgibbs

Joined Jan 29, 2010
18,011
hi P,
That was a good solution,
E