Implementing IC's on PCB?

Electroenthusiast · Mar 19, 2010

What are the rules to be followed to implement a IC(...like 74 series) on Genral purpose PCB,
i need use 74193 in my circuit, and i have done with the design.

But my problem is i dont know how to implement IC's Practically (Connections the i need to make, to exclude High impedance state etc.,).

ericgibbs · Mar 19, 2010

r.vittalkiran said:
What are the rules to be followed to implement a IC(...like 74 series) on Genral purpose PCB,
i need use 74193 in my circuit, and i have done with the design.

But my problem is i dont know how to implement IC's Practically (Connections the i need to make, to exclude High impedance state etc.,).

Please post the circuit diagram.

Electroenthusiast · Mar 19, 2010

ericgibbs said:
Please post the circuit diagram.

Here it is...also tell me where all i should use pull-down resistors,
i tried the design in a breadboard, but there was something wrong,
so i've posted this thread

ericgibbs · Mar 19, 2010

r.vittalkiran said:
Here it is...also tell me where all i should use pull-down resistors,
i tried the design in a breadboard, but there was something wrong,
so i've posted this thread

hi,
Looking over your diagram.
The DEMUX, what type of IC is it.?

The 74193 requires that when clocking the unclocked pin must be high.

Electroenthusiast · Mar 19, 2010

ericgibbs said:
hi,
Looking over your diagram.
The DEMUX, what type of IC is it.?

Hi!
I'm going to design it using "Basic Logic Gates"

ericgibbs said:
The 74193 requires that when clocking the unclocked pin must be high.

can u please elaborate... how can i do it? Pull-Up resistor?? HOW???
PLS

ericgibbs · Mar 19, 2010

r.vittalkiran said:
Hi!
I'm going to design it using "Basic Logic Gates"

can u please elaborate... how can i do it? Pull-Up resistor?? HOW???
PLS

hi,
Gate outputs are normally pulled low or high.
You have to devise a logic gate combination that keeps the unused clock input held high while the other clock input is being clocked on a rising edge.

Do you follow OK.

BTW: do you plan to use the parallel load pin.?
Also have you got the CLEAR pin held low.?

EDIT:
Hint. Consider using NAND logic gates. Lets know how it goes.

Electroenthusiast · Mar 19, 2010

ericgibbs said:
hi,
Gate outputs are normally pulled low or high.

Does this mean 'i have to use pull up/ pull down resistors at output'?

ericgibbs said:
hi,
Gate outputs are normally pulled low or high.
You have to devise a logic gate combination that keeps the unused clock input held high while the other clock input is being clocked on a rising edge.

I may have to use Pull-down resistors for this, if i'm correct...
may i know should i use pull-down resistors in all inputs of IC, so that i will eliminate High input state?

ericgibbs said:
hi,
BTW: do you plan to use the parallel load pin.?
Also have you got the CLEAR pin held low.?

I'm not using "LOAD", "Borrow", "Carry"...

Yes, i'l use pull down resistor for "Clear"

ericgibbs said:
hi,
EDIT:
Hint. Consider using NAND logic gates. Lets know how it goes.

What? I didn get you?

audioguru · Mar 19, 2010

74xx ICs are extremely old. Nobody uses them today except school kids. They need a regulated 5V supply, use a high supply current and a high input current.
Maybe you should use CD4xxx Cmos logic ICs. They work from an unregulated 3V to 18V supply and their supply current is almost nothing. Their input current is nothing.

ericgibbs · Mar 20, 2010

r.vittalkiran said:
Does this mean 'i have to use pull up/ pull down resistors at output'?
No.

I may have to use Pull-down resistors for this, if i'm correct...
may i know should i use pull-down resistors in all inputs of IC, so that i will eliminate High input state?
No

I'm not using "LOAD"
Use a 1K resistor to +5v to hold this pin high, if not being used

Yes, i'l use pull down resistor for "Clear"
Connect directly to 0V, if you dont plan to use Clear/Reset

What? I didn get you?

hi,
Look at this image for one option for gating the clock.

Electroenthusiast · Mar 20, 2010

ericgibbs said:
hi,
Look at this image for one option for gating the clock.
View attachment 40407

mmm...thanks, may i know any book, through which i can know "How to use IC's Practically?", / or a website will do...

I'l be uploading my actual design in few moments....

ericgibbs · Mar 20, 2010

r.vittalkiran said:
mmm...thanks sir, may i know any book, through which i can know "How to use IC's Practically?", / or a website will do...

I'l be uploading my actual design in few moments....

hi,
These links may help.

Digital Logic - Gates, Boolean Algebra

Free Electronics resouces: tutorials, datasheets, software, websites - Freebyte's Guide to

Bob Bowman's Free Educational Technologies: Votech Links

Electroenthusiast · Mar 20, 2010

Here's what i want to do...
Roughly Written

Hope design works!

ericgibbs · Mar 20, 2010

r.vittalkiran said:
Sir, Here's what i want to do...
Roughly Written
View attachment 40438

Hope design works!

hi,
The resistors on the S and R are not required.

Is the 1:2 MUX the circuit I posted.?

Electroenthusiast · Mar 20, 2010

Can i know how i can Solder(Conections) this in PCB?

ericgibbs said:
hi,
The resistors on the S and R are not required.

i may have to use it because i need the
"previous state as output" when there is no input...
(Because there will be no input at some times...
and 74279 does'nt have pull-down resistor embedded in it...)
May i know why u told so?

ericgibbs said:
hi,
Is the 1:2 MUX the circuit I posted.?

Yes, Mostly ...

audioguru · Mar 20, 2010

You are living in a very different world than most of us (in India?). Most of your parts are extremely old. We strain to remember them.
Only school kids from India call us SIR. A SIR is somebody who was Knighted by the Queen Of England.

A very old fashioned 74xxxx IC needs a very high input current to ground for its input to be seen as a logic low. The input must be forced to 0V with 1.6mA to make it low.

danrogers · Mar 20, 2010

Guru, you are a living legend lol

Electroenthusiast · Mar 20, 2010

audioguru said:
You are living in a very different world than most of us (in India?). Most of your parts are extremely old. We strain to remember them.
*********** India call us SIR. A SIR is somebody who was Knighted by the Queen Of England *******

Ya from India! It's something like giving respect to an elderly person...
I'm sorry if it hurt you, i'l never be calling so to anybody here, from now on!

audioguru said:
A very old fashioned 74xxxx IC needs a very high input current to ground for its input to be seen as a logic low. The input must be forced to 0V with 1.6mA to make it low.

Can you please elaborate,... i dont know why "1.6mA" is required to Ground an Input

ericgibbs · Mar 21, 2010

r.vittalkiran said:
Ya from India! It's something like giving respect to an elderly person...
I'm sorry if it hurt you, i'l never be calling so to anybody here, from now on!
Can you please elaborate,... i dont know why "1.6mA" is required to Ground an Input

hi,
Please call me whatever you wish, Eric would get the job done.

If the S/R is TTL, the open circuit inputs will assume a logic high, as 'agu' points out to pull the TTL input to a logic low the PullDown resistor must draw 1.3mA from the TTL input.
I would not normally recommend using PD resistors on TTL inputs.

For Reference:
In a high speed logic circuit I would recommend you do not leave TTL inputs, whose outputs are connected to a following device input, open circuit. [Floating]
This could cause mis-operation of the circuit due to electrical 'noise'

Why not just build the circuit from the details you have been given.

Hero999 · Mar 21, 2010

r.vittalkiran said:
Ya from India! It's something like giving respect to an elderly person...

Same in England to some extent.

Schoolchildren call their teacher sir.

I'm sorry if it hurt you, i'l never be calling so to anybody here, from now on!

I doubt you've offended anyone, we just find it funny.

ericgibbs said:
Please call me whatever you wish, Eric would get the job done.

I can think of lots of things to call you buy unfortunately they're against the forum rules.

r.vittalkiran said:
and 74279 does'nt have pull-down resistor embedded in it...)
May i know why u told so?

Just imagine that all TTL inputs have built-in pull-up resistors so in order to pull an input low you need a pull-down resistor which will draw the 1.3mA Mr Gibbs sir was talking about, in order to make the voltage low enough for the input to be low.

ericgibbs · Mar 21, 2010

Hero999 said:
I can think of lots of things to call you buy unfortunately they're against the forum rules.

Ouch.! that smarts, does this mean I am no longer on your Christmas gift list.

BTW: did you hear the latest Govt fudge word, the unemployed are categorised as 'economically inactive', it means they can juggle with the unemployment figures even more.!!

Implementing IC's on PCB?

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