divide by 10

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Newz2000
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divide by 10

Post by Newz2000 » Thu Nov 10, 2005 12:16 pm

I'm creating a circuit based on a 555 astable that will pulse at a variable speed similar to the firing of the ignition coil on a car. I'm doing this so that I can test a PIC based tachometer circuit.

The timer will send a square wave at a rate of between 12Hz and 245Hz (20 - 200 was my goal, to emulate 600 - 6,000 rpms).

Besides my 5v output I've also got an LED in the circuit, however the LED blinks too fast. At approximately 12Hz you can tell it's flashing (vs. solid on) but at anything higher you can't tell if it's 50 or 150 Hz.

What is the simplest way to cause there to be 1 LED pulse for every 10Hz on the square wave? I'm going for:

Code: Select all

LED off
 pulse 1
 pulse 2
 ...
 pulse 10
 LED on
 pulse 1
 pulse 2
 ...
 pulse 10
 LED off
Because the square wave will be a variable frequency, I can't assume that the 10th pulse will occur at a set time interval.

It doesn't have to strictly be 10, by the way. If it's easier to do 8 or 16, that is fine. I have a bunch of 74HC parts, also I have some shift registers. I have a spare 555 timer and more resistors and capacitors than you can shake a stick at. I think I have an Atmel 24c02 eeprom too.

You know my end result - I have the 555 timer circuit already bread boarded, but if you know a better way to make my pseudo ignition coil that will produce a pulse in the range of 20 - 200 Hz (doesn't even need to be square) and allow blinking of an LED at a 10th of that value, I'm open to suggestions.

Michael J
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Re: divide by 10

Post by Michael J » Thu Nov 10, 2005 12:33 pm

Hi Mat, you could use a 4017 to divide by 10
or 2, 3, 4 ,5, 6, 7, 8, 9.
If not by 10 just take the last output used
back to pin (15 from memory) to reset the count.

Whatever O/P you use via a current limiting
resistor and LED to GND.
1k - 1k2 Ohms for 12V
330 - 560 Ohms for 5V

<small>[ November 10, 2005, 12:39 PM: Message edited by: Michael J ]</small>

Newz2000
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Re: divide by 10

Post by Newz2000 » Thu Nov 10, 2005 12:40 pm

I don't have that one. :(

I could get one of these cheap and easy:
In stock at radio shack (believe or not).
74HCT273 Octal D-type Flip-Flop w/Clear 20 Pin DIP
$0.48

<small>[ November 10, 2005, 12:48 PM: Message edited by: Matt Nuzum ]</small>

Michael J
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Re: divide by 10

Post by Michael J » Thu Nov 10, 2005 1:03 pm

4017 is one of the most common chips on the planet.

You could try a 4040 or 4060, they divide by
4, 8, 16, 32, 64 etc.

With something like the above you can select
a different O/P for fast or slower timing speeds.

Engineer1138
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Re: divide by 10

Post by Engineer1138 » Thu Nov 10, 2005 1:48 pm

The 74LS90 is a decade counter that was popular with 7-segment display drivers. Radio Shack used to carry them and some still may.

Newz2000
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Re: divide by 10

Post by Newz2000 » Thu Nov 10, 2005 2:01 pm

I've got a 74HC4060! Now just have to figure out how to use it...

I've only used the 74HC chips in kits where the instructions say, "now insert the..." but never explain what it does. So, I have no idea what a binary 14 stage ripple counter is. So let's see,
The oscillator may be replaced by an external clock signal at input RS. In this case keep the other oscillator pins (RTC and CTC) floating.
...
ten buffered outputs and an overriding synchronous master reset
I see in the data sheet that it increments the counter on the falling edge, however I don't see any details of what the thing does.

Can you suggest a reference that would explain how to use this? It seems that this is a counter, so instead of having one output active at a time it counts up in binary, so in that case, I'd probably want to divide by 8 or 16 wouldn't I? That way if I want to divide by 8 I could set the 3rd output to turn the LED on and the 4th output to reset the count (although I really don't know how to do that yet, I'm just hypothesizing based on what it sounds like this thing does). If I wanted to divide by 16 I'd use the 4th and 5th bits, right?

Also, the datasheet doesn't seem to tell how much current the buffered outputs can sink or source. Do I have enough leeway to turn on an LED?

Also, the datasheet doesn't say what to do with unused outputs. Bring them high? Low? Floating?

I'm glad to know there's a solution that I have the part for, however now I have lots of questions.

<small>[ November 10, 2005, 02:05 PM: Message edited by: Matt Nuzum ]</small>

Newz2000
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Re: divide by 10

Post by Newz2000 » Thu Nov 10, 2005 2:07 pm

Oh, it looks like the output can handle +/- 5.2ma. That's ok, I have a bright LED that I can current limit down to 4ma and still see.

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Edd
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Re: divide by 10

Post by Edd » Thu Nov 10, 2005 6:40 pm

Instruccionnes:

Disregard the internal osc pins of 9 and 10. Power up the chip from pins 8(-) and 16(+) using both short lead HF and LF bypassing filtering capacitors.(10 UFD or up and .1 disc ceramic)
Insert your monitored variable freq signal into clock input number 11 , possibly thru a 1-10k isolation resistor, all in accordance to your drive level.
Pin 12…reset…. Is grounded.
Q4 …pin ..7 will supply your fastest divide by 16 output to further drive a LED or as slow as divide by 16,384 may be had at pin 3. (With time to also watch a movie and get back to see the LED blip.)

Glitches may occur in any logic gate due to the slight delay before the later counter outputs respond to a clock pulse, BUT this should not be of any consequence in your simple application of merely wanting a divided/slowed down visual display of an ensuing pulse train sequence.

Da Da sheet:
http://www.semiconductors.philips.com/a ... _CNV_2.pdf

73's de Edd
[email protected] .........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled*Spam*Cookies*Crumbs)
:D

<small>[ November 10, 2005, 06:46 PM: Message edited by: Edd Whatley ]</small>

Newz2000
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Re: divide by 10

Post by Newz2000 » Thu Nov 10, 2005 8:34 pm

It's getting too hot. Here's what I have:

a 555 timer circuit that should be pulsing at about 15hz to an LED (the light looks dimmed and somewhat flickery, so this seems reasonable). The LED is a standard green 3mm with a 1k resitor and the kathode goes to ground (so it's sourcing current).

The LED/resistor are connected to pin 3 on the 555.

Also connected to pin 3 on the 555 is the 74HC4060N.

The 4060 has an LED connected from pin 5 through a 4.7k resistor and goes to ground.
Pin 8 goes to ground.
Pin 11 comes from the 555 timer via 2.2k ohm resistor
Pin 12 goes to ground
Pin 16 goes to +5v.

At first I had the LED hooked up to pin 7 via 470 ohm resistor. The LED stayed lit, then, after 10 seconds it went out. It didn't come back on. I touched the 4060 and realized it was way too hot so turned it off. I haven't been able to repeat the experience of the LED being lit on pin 7. However, I exchanged the resistor and tried it on pin 5 and now the LED is on. I've only tried it for a few seconds because the chip is still getting very hot. Too hot too touch - my finger still feels singed from when I touched it the first time.

Newz2000
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Re: divide by 10

Post by Newz2000 » Thu Nov 10, 2005 8:42 pm

Hmmm... when I remove the connection from the 555 to the 4060 the LED connected from pin 5 on the 4060 stays lit.

Did I pull too much current through the 4060 the first time with my 470 ohm resistor/green LED and burn it up? I hate it when I do that.

----- \me smacks head
Doh! Or maybe it's getting so hot because I had it hooked up to 12v instead of 5v.

Argh. Well, let's see if it's dead or not.

<small>[ November 10, 2005, 08:45 PM: Message edited by: Matt Nuzum ]</small>

jimandy
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Re: divide by 10

Post by jimandy » Thu Nov 10, 2005 9:06 pm

I think for divide by 16 your output should be on pin 7 not pin 5 No output pins should be grounded.

I'm thinking you had a good idea in earlier post, connect the output pin you use (7? 5?) to the reset line.

If you have an old style (analog) meter, remove the led and probe your output pin and at low enough clock frequency the needle will tell you if the chip is dividing.
"if it's not another it's one thing."

Michael J
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Re: divide by 10

Post by Michael J » Thu Nov 10, 2005 9:39 pm

If you have blown up the chip get a CMOS version
next time, they work from 3 to 18V, less headaches.

You don't have to worry about grounding the unused outputs and they (O/P) will happily
drive an LED.

<small>[ November 10, 2005, 09:45 PM: Message edited by: Michael J ]</small>

jimandy
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Re: divide by 10

Post by jimandy » Thu Nov 10, 2005 10:06 pm

Hey, Michael j. Isn't a 74HC4060 CMOS (the "C" being the clue) ?

<small>[ November 10, 2005, 10:06 PM: Message edited by: jimandy ]</small>
"if it's not another it's one thing."

Michael J
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Re: divide by 10

Post by Michael J » Fri Nov 11, 2005 12:49 am

Matt, I should have said use an MC14060 or MC14040, shame on me.

Jimandy I saw the 74 and figured TTL.

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Re: divide by 10

Post by jimandy » Fri Nov 11, 2005 8:24 am

Actually, Matt. You might simplify your test board circuit altogether by using the built in oscillator of the 4060 (assuming it's not toast) and eliminating the 555. Then pick your outputs, one for the simulated tach freq. and the next one up for the divided down LED driver.
"if it's not another it's one thing."

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