how to connect 74HC192 to PL

[electricalnomad]

Dear all, I am trying to make a BCD counter decrementing from any number, max 99 decremetning to 00 and then starting back again. the number I want to begin with for example 55 to 00 is determined using dipswitches. I have succesfuly connected the circuit having 2 74HC192, 7447 and 2 seven seg displays. I cannot find a way for the circuit to begin counting from were I want it. there reason I think is due to the PL connectioon. please can someone help me. i have been searching and trying alot
tnk u

 

[ericgibbs]

Dear all, I am trying to make a BCD counter decrementing from any number, max 99 decremetning to 00 and then starting back again. the number I want to begin with for example 55 to 00 is determined using dipswitches. I have succesfuly connected the circuit having 2 74HC192, 7447 and 2 seven seg displays. I cannot find a way for the circuit to begin counting from were I want it. there reason I think is due to the PL connectioon. please can someone help me. i have been searching and trying alot
tnk u

hi,
Can you post your circuit diagram.?

 

[electricalnomad]

here it is. the problem is connecting to PL. i have tried many different combiantional gates but still havent solved the problem.
thank you

 

[ericgibbs]

here it is. the problem is connecting to PL. i have tried many different combiantional gates but still havent solved the problem.
thank you

hi,
Your diagram shows that the HC192 /PL pin is floating, not connected.???

To load/preset the HC192 counter you must pulse the /PL low after setting the bit switches to the required value.

 

[electricalnomad]

here it is. the problem is connecting to PL. i have tried many different combiantional gates but still havent solved the problem.
thank you

Yes I know that it is floating, since I tried several different ways. but what do you mean by pulse the /PL low?? by setting a low state to it??? or a dpattern to it?

thank you

 

[ericgibbs]

Yes I know that it is floating, since I tried several different ways. but what do you mean by pulse the /PL low?? by setting a low state to it??? or a dpattern to it?

thank you

hi,
If you set it low all the time it will always be the same count, the one you loaded.
Use a simple switch push button with say a 2.2K resistor and a 100nF cap, push the switch to /PL the counters.
OK.?

 

[electricalnomad]

hi,
If you set it low all the time it will always be the same count, the one you loaded.
Use a simple switch push button with say a 2.2K resistor and a 100nF cap, push the switch to /PL the counters.
OK.?

View attachment 41178

I connected the circuit as you told me and is now working good when I press the 'button' switch. when I arrange the dipswitches for me to give me for example 26 to decrease to 25 24 23 23....00 it works fine. but my only trouble now is that when it goes to 00 it starts back to the maximun number, i.e. 99 and not where it was saved before, i.e. for example 26. thank you for your help
It is very much appreciated.
attach is my cct diagram, I did not conect the capactiror to the switch but connected a 10k resistor instead.

now i am trying to figure out how I can 'save' my number when it restarts.
THANK YOU

 

[electricalnomad]

hi,
If you set it low all the time it will always be the same count, the one you loaded.
Use a simple switch push button with say a 2.2K resistor and a 100nF cap, push the switch to /PL the counters.
OK.?

View attachment 41178

I have succesfully connected the cct now with the RC cct and an inverter so that when the ounter starts it automatically begins with the desired value from the dip switches and then after the switch is pressed it will continue.
my prob now is how am i going to connect the cct and add logic to it in such a way to remember before.
I think it has to be using ff but still i can;t figure out the right solution.

the cct is now attached.

 

[ericgibbs]

I connected the circuit as you told me and is now working good when I press the 'button' switch. when I arrange the dipswitches for me to give me for example 26 to decrease to 25 24 23 23....00 it works fine. but my only trouble now is that when it goes to 00 it starts back to the maximun number, i.e. 99 and not where it was saved before, i.e. for example 26. thank you for your help
It is very much appreciated.
attach is my cct diagram, I did not conect the capactiror to the switch but connected a 10k resistor instead.

now i am trying to figure out how I can 'save' my number when it restarts.
THANK YOU

hi,
If you want to auto parallel load the switch count when the counters reach 00, you need to combine the /TC on both LS192 and use that to generate a /PL pulse.
That will reload the counters. You will have to use logic gate so combine the two outputs.
OK.?

 

[electricalnomad]

hi,
If you want to auto parallel load the switch count when the counters reach 00, you need to combine the /TC on both LS192 and use that to generate a /PL pulse.
That will reload the counters. You will have to use logic gate so combine the two outputs.
OK.?

Analysing the cct when the counter is 00, the /TCD are both low. thereefore I added gates in order for the /TCD to be always high. since Q1 and Q3 are never both low (BCD of 0-9) an nand gate was inserted. this was done for both the ics. and then added to an and gate as can see from the picture.

It now works fine.
the only thing that I can not understand is since the /PL requires a LOW to read from the inputs. I am confused since the /PL requires a low to read from the inputs. so if it is LOW (blue sign on Proteus), this means that it is HIGH??SINCE IT IS NOTTED. i dont think but i am confused. if /PL requires a LOW, then I think a low is needed and not a high
attached is my cct.

THANK YOU

 

[ericgibbs]

hi,
Pleased to hear its working.
Are you sure that the push PL switch is drawn correctly.?
When the switch is not pressed , U10:C pin 10 is Low, so U10:C pin8 is Low, thats the /PL line.???

 

[electricalnomad]

hi,
Pleased to hear its working.
Are you sure that the push PL switch is drawn correctly.?
When the switch is not pressed , U10:C pin 10 is Low, so U10:C pin8 is Low, thats the /PL line.???

I think you are reffering to U8:C not U10:C.
Yes when switch not pressed, /PL is low therefore it reads the Dip switch input.
when the switch is pressed it starts working. you think it is wrong?
thnku

 

[ericgibbs]

I think you are reffering to U8:C not U10:C.
Yes when switch not pressed, /PL is low therefore it reads the Dip switch input.
when the switch is pressed it starts working. you think it is wrong?
thnku

Yes that should be U8.
If you look at the LS192 datasheet internal circuit it shows the /PL [not PL] is asynchronous and its gated with P0,1,2,4 inputs and the inverted RESET.
This means if the /PL is low and active, the counter should not be able to count up or down.

 

[electricalnomad]

Yes that should be U8.
If you look at the LS192 datasheet internal circuit it shows the /PL [not PL] is asynchronous and its gated with P0,1,2,4 inputs and the inverted RESET.
This means if the /PL is low and active, the counter should not be able to count up or down.

Yes yes, the switch is not pressed before the user adjusts the dipswitch for the number he wants. then the user presses the swithch and begins counting down.
it ok isn't it?
Thank you

 

[ericgibbs]

Yes yes, the switch is not pressed before the user adjusts the dipswitch for the number he wants. then the user presses the swithch and begins counting down.
it ok isn't it?
Thank you

Are you using the normally closed contacts on the PL switch.?
So when the switch is operated the contacts open, this would make sense.

 

[electricalnomad]

Are you using the normally closed contacts on the PL switch.?
So when the switch is operated the contacts open, this would make sense.

I am saying that if swith is not pressed, only the number is shown and there will be no counting (downward). then the user presses the switch and /PL always keeps high.
It works fine. but i hope it is good, since I am not uinderstanding you very much.
tnx

 

[ericgibbs]

I am saying that if swith is not pressed, only the number is shown and there will be no counting (downward). then the user presses the switch and /PL always keeps high.
It works fine. but i hope it is good, since I am not uinderstanding you very much.
tnx

OK,
So the user operates the switch, which makes /PL high and then counting is allowed while the switch is pressed.

Are you now satisfied with the circuits operation.?

 

[electricalnomad]

OK,
So the user operates the switch, which makes /PL high and then counting is allowed while the switch is pressed.

Are you now satisfied with the circuits operation.?

Yes!!!!!!!
I am very satisfied. I conected it to a 555 timer to give adelayy of 5 seconds when the counter restarts.
thank you very much!!!!!!!!!!!!