Hi all
i found this circuit design
http://www.schematicsforfree.com/arc...l%20clocks.pdf

and i was wondering, what's going on with the 7404 ? The description says it is used as the clock, but i cant imagine that. Doesnt the circuit need a timer or a sin wave input?


If the link doesnt work, go to www.schematicsforfree.com then click on "show the files" and then go to the "clocks" section and u will find the design there.

 

No, it doesnt need any other input for the clock. The RC circuit (with the 7404) is an oscillator that generates the clock. I doubt its very accurate.

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Jeff Zimmerman
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass is twice as big as it needs to be.

 

Could i use something else instead of the hex inverter?
like a 555 or something?

oh and i was wondering how he came up with the specific values for the capacitors and the resistors (even though u say its not that accurate)

 

The circuit is 26 years old and uses old-fashioned TTL logic ICs.
Make a more modern circuit with Cmos ICs.

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Uncle $crooge

 

Well its a university project and i need to use ttl logic 74xx series ICs...

 

Is that because that's what you have in stock?

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Ron (aka Rube)

 

the teacher says 74xx series, then 74xx series it is.

 

If it's OK to use a 555, then that will work for your clock generator, in place of the 7404.

__________________
Ron (aka Rube)

 

Thanks Appleseed for a great link re the schematics.

__________________
There are more ways to get to Rome.

Electricity, Electric clocks, Meters and Trains are great.

 

It doesn't have to be accurate, there is no link between the pendulum and the clock.

It just simulates a pendulum. It won't tick in sync with the clocks second hand, if the clock even has one.

 

he's right it doesnt have to be really accurate. oh and there will be no clock after all

 

I kind of suspect the teacher would accept a 74HC04. when some one says 74xx logic, they often just mean any of the logic families. why not ask?

 

A 74HC04 might melt if it is used instead of a 7404 in that oscillator circuit.
74HCxx inputs have a max 450ns spec'd amount of time that they are allowed to spend in the linear region. 74HCxx ICs with schmitt-trigger inputs are recommended for oscillators.

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Uncle $crooge

 

so, what do you suggest?

 

My Ultra-bright LED Chaser projects use 74HCxx Schmitt trigger oscillators and work fine.

But your problem is: "the teacher says 74xx series, then 74xx series it is".

If I was doing it, I would build the 74xx circuit and power it from a car battery, and make another with 74HCxx and power it with a little battery.
The old 74xx ICs wasted a lot of power. The newer 74HCxx ICs use hardly any power.

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Uncle $crooge