LED Pendulum circuit

[appleseed]

Hi all
i found this circuit design
**broken link removed**

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.

 

[jrz126]

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.

 

[appleseed]

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)

 

[audioguru]

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

 

[appleseed]

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

 

[Roff]

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?

 

[appleseed]

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

 

[Roff]

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.

 

[RODALCO]

Schematics

Thanks Appleseed for a great link re the schematics.

 

[StopGo]

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.

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.

 

[appleseed]

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

 

[philba]

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?

 

[audioguru]

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.

 

[appleseed]

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.

so, what do you suggest?

 

[audioguru]

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.

 

[appleseed]

what about the 74LS

 

[audioguru]

what about the 74LS

Good idea!

I made circuits with LS all the time until I switched to Cmos. LS was fast and had a much lower supply current than ordinary TTL.
But Cmos can't be beat for low power consumption at low speeds:

 

[milpitor]

TTL runs between 7-15DCV
CMOS runs between 3-7DCV
Correct me if I'm wrong.

 

[Nigel Goodwin]

TTL runs between 7-15DCV
CMOS runs between 3-7DCV
Correct me if I'm wrong.

VERY, VERY, WRONG!.

Try reading the datasheets!.

 

[RODALCO]

TTL only 5 Volts DC !!