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Can someone provide me a simple timer schematic?

 
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Can someone provide me a simple timer schematic?
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Recon Blazer
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Post Can someone provide me a simple timer schematic? Reply with quote
I've learned some stuff since I last posted here, and I feel I am ready to start working on schematics now. I have a good grasp on Ohm's Law, resistance, capacitors, symbols and stuff.

I was at my local Radio Shack the other day, and they had cheap ICs on clearance, so I picked up 5. They are all CMOS high-speed logic chips.

Anyway, I'm not sure if any of them will control an LED. I need a simple circuit that utilizes a 555c timer that counts seconds 0-9 and displays them on an LED. If you need the specs on my 555c timer and LED, I can provide them.

Radio Shack #: 276-1723 555CN timer:
18V max
4.5-16V typ.
power dissipation: 600mW
Output current (sink or source): 200mA

276-075 LED max ratings:
Forward current: 30mA
Forward voltage: 2V
Reverse voltage: 5V
Power dissipation: 100mW

Typical:
Forward current: 20mA
Forward voltage: 1.7V
Peak wavelength: 655nm

Here is the model number/series of one chip in particular. 74HCT541 Octal Buffer/Line driver; 3-state. I am not sure if this would make the LED work or not.

All I want to learn from this project is how to make an LED work, as well as actually using the timer. Thanks alot. Drool

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Fri Sep 10, 2004 11:54 pm View user's profile Send private message AIM Address
pcs
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Post Reply with quote
Hi there!

I see you're eager to learn about electronics and are
also willing to invest some effort. Don't give up, keep
learning. You are at the beginning of a road that may
seem difficult in the beginning, but the rewards are
plentifull =D>

Now, let's look at your problem.

The NE555 chip may be used to generate ~1s pulses, but they
are going to be determined by things such as R and C values,
which are not accurate (10-20% tolerance).
The frequency/accuracy will also depend
on temperature & supply voltage. In short, your 1 second pulses
will probably not be accurate. This may be important or not for you.


The proper way to get accurate 1s pulses is to use quartz crystal.
These are extremely stable and are used in such things as wrist
watches, telecommunications equipment etc.

You won't be able to find 1Hz quartz as this is not possible/practical
to manufacture, they are available at much higher frequenies, say
1MHz. What you do than is use divider chip to get it down to 1Hz.

Now, the thing with these divider chips (counters) is that they are
easier to implement in binary mode, meaning you get division
ration such as /2, /4, /8 ...... /1024, /2048....

This means that you also need a quartz with suitable frequency,
ie not 4.000 MHz, but rather 2.048MHz (/2048 gets you 1KHz precisely).
Fortunately these are plentifull for various typical frequencies.

What I recommend to you is that you use the 4060 chip, it is a binary
counter with oscillator which can also be made with quartz crystal.
I would suggest using the lowest frequency available quartz, which is
the 32768Khz (used in wrist watches). This way you'll get 2Hz out
of the 4060 (largest divide ratio is /16384).

http://www.mcamafia.de/nixie/images/nix_1hz.jpg
I've googled it up for you, you'll notice the additional divider by 2
to get it to 1Hz which is 1s pulse.

In fact, the whole page is interesting:
http://www.mcamafia.de/nixie/ncp_en/ncp.htm


Now you've got 1s pulses, but you still need to to power your display.
To do this you need decade counter, a counter which counts from 0
to 9. A good example would be 7490. The output of this counter will
be 4-bit decade code. Almost the same as binary, but only goes
up to 9 and then jumps back to 0.

You can't power display with this directly, so you need decade to
7- segment decoder, such as 7447. Here is the datasheet:
http://www.ee.washington.edu/stores/DataSheets/74ls/74ls47.pdf
And here is how to connect it:
http://travel.howstuffworks.com/digital-clock7.htm
This should help, too:
http://espresso.ps.admu.edu.ph/faculty/tris/display.gif


This is one good resource on theory about all this:
http://www.msoe.edu/eecs/ee/misc/100/logic_devices.doc


All this can also be done with one microcontroller.
http://chaokhun.kmitl.ac.th/~kswichit/clock/clock.htm
Its a small microprocessor with program memory and output pins
that can be directly used to control display.
As you see these make your devices much simpler and you can
program them to do anything you want so I really recommend these
to you. They open up a whole new universe for you and the initial steep
learning curve is well worth it.


Now I've given you some stuff to study so this should be a busy
weekend for you

Come back with questions when you've processed all that

And check our new schematics section, many ideas there also:
http://www.pcs-electronics.com/en/guide.php?sub=NewSchematics

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Best regards,
Marko - PCS Electronics
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Sat Sep 11, 2004 10:08 am View user's profile Send private message Visit poster's website
Recon Blazer
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Post Reply with quote
<i>What I recommend to you is that you use the 4060 chip, it is a binary
counter with oscillator which can also be made with quartz crystal.
I would suggest using the lowest frequency available quartz, which is
the 32768Khz (used in wrist watches). This way you'll get 2Hz out
of the 4060 (largest divide ratio is /16384). </i>

Thanks for your prompt reply. I"ve been looking at Jameco and other places for the parts you gave. I have a question, though.

Up above, you talk about the 4060. From what you said, I can't tell if the chip is made with the 32768Khz, and when you said made with quartz crystal, did you mean it can be made to work with the crystal, or it can be made with it inside it? Also, you're saying that a counter chip works as a divider?

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Fri Sep 17, 2004 5:40 pm View user's profile Send private message AIM Address
Recon Blazer
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Post Reply with quote
<i>32768Khz (used in wrist watches). This way you'll get 2Hz out
of the 4060 (largest divide ratio is /16384). </i>

Do you mean 32,768hz, or 32,768Khz (32.768Mhz)?

If its 32,768Khz, then

32,768Khz = 32,768,000hz /16384=2000

Or did you mean 32,768hz?

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Fri Sep 17, 2004 5:47 pm View user's profile Send private message AIM Address
pcs
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Post Reply with quote
, is decimal point where we live. I know you use a dot

So, it is 32768 Hz, to avoid confusion.

The chip by itself does not oscilate, you need to add a couple
components and quartz crystal. See the links for schematics.

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
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Recon Blazer
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Post Reply with quote
Ok, that makes it alot better =D>

I think I can see the decimal in the hz for the schematic. It's kind of blurry if you zoom in.

I'm guessing that the capacitor on the right is a variable capacitor. The symbol in my college electronics book uses an arrow instead. Also, on first glance, I thought it said 4.40pF, but now I notice that the dot is centered vertically. What does that mean? I haven't seen that yet in my reading. I also am guessing that the symbols with the flat lines are ground, or point of common connection? I haven't seen those symbols in my reading, either. I don't know why there isn't just one standardized variation for symbols. And the arrows pointing up are connected at some point, right?

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Recon Blazer
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Post Reply with quote
<i>Ok, that makes it alot better Applause

I think I can see the decimal in the hz for the schematic. It's kind of blurry if you zoom in.

I'm guessing that the capacitor on the right is a variable capacitor. The symbol in my college electronics book uses an arrow instead. Also, on first glance, I thought it said 4.40pF, but now I notice that the dot is centered vertically. What does that mean? I haven't seen that yet in my reading. I also am guessing that the symbols with the flat lines are ground, or point of common connection? I haven't seen those symbols in my reading, either. I don't know why there isn't just one standardized variation for symbols. And the arrows pointing up are connected at some point, right?</i>

Nevermind, it's trimmer

But I'm still wondering about the dot, and the other stuff, cuz I still can't find those symbols anywhere.

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Fri Sep 17, 2004 7:57 pm View user's profile Send private message AIM Address
Recon Blazer
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Post Reply with quote
Ok I ordered and received a 4060, 4013, 7490, and a 7447, as well as a 32.768K crystal.

I built the 1Hz pulse circuit, and it works just fine. However, When I connected the 7490, 7447 and the 7-segment LED, the LED does not light up. To test the 1Hz part of it, I connected an LED to it, and it flashes on and off.

According to the schematics you provided for the 7490 and 7447, the LED and all three are hooked up right. One thing I noticed, however, is no schematic tells what the voltage should be.

I tried 3V, 6V and 9V, and neither made the 7LED light up.

Why isn't this part working, when there is a 1Hz pulse?

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Engineer_Leo
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Post Making an LED Light Reply with quote
You've probably figured it out by now. But, the most common error in making anLED light is forgettimg to use a "pull-up" resistor. A 1K Ohm should do the trick. From Vcc to the 1K Ohm in series with the LED and the other side of the LED to ground. This circuit will simply light the LED.

Cheers
Sun Jan 08, 2006 2:54 am View user's profile Send private message
sheldonstv
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Post Reply with quote
the crystal is a 32.768 khz crystal(??)....im going to use this circuit without the 4013 to clock a 4020 shift register and will use pin 6 to give me a pulse every minute for a repeating timer im building.....useful things these shift registers
regards mike
Wed Sep 27, 2006 1:26 pm View user's profile Send private message
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