LED Flasher with Variable Flash Times

If you'll provide me with the details, I'll do it. I can generally construct circuits, but don't know how to design them.

Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA) (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time) Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

--
                     "Predictions are hard to make. Especially
                      about the future. -- Yogi Berra

                     Web Page:

4060 chip if they have it.

Bye. Jasen

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Go for a chip that will count to a large number and trigger it with a 555 that can easily be adjusted to provide a pulse frequency that makes the counter complete its sequence in the time that you require.

R

One possibility would be a CD4541 chip. It is both a timer and a counter, combined into a single IC. You use a cap and two resistors to set the clock frequency, and two pins to set the output division ratio. There are

4 possibilites: 8192, 1024, 245, and 65526.

The clock frequency is related to the timing cap and resistor as

f = 1/(2.3*Rt*Ct).

So, lets assume you want a 15 minute flash. Then you'll need a rising pulse every 15 minutes, so the end frequency is 1/900. By using the 65536 divider, need the timer to produce a frequency of

1/900 * 65536 = 72.8Hz. So, using the formula above,

f = 72.8Hz = 1/(2.3*Rt*Ct). Choosing Ct=0.1uF, we have

Rt = 59k. Picking a resistance value that is close, you use 62k. The other resistor should be 2x the first, so pick 120k.

The other problem is what to do about the pulse. The chip will give you a nice 1/900 Hz square wave, meaning it'll be high for 7.5 minutes, and low for 7.5 minutes.

One easy solution to this is to use an SCR. Trigger it through a capacitor, and

Vcc (4.5V?) ----------------------------. | | [220k] | WHITE LED | .----|

--
When you say "flasher" do you mean that your camera can be triggered
by a flash of light and you need something that flashes an LED every
once in a while for a certain amount of time or do you need a
contact closure to trigger the camera? 

In either case, what should the width of the trigger be?

--- Try this: (view in Courier)

+---------+-----+------+ | Vcc | | | [100K] | +-->[100k][0.12µF] | [100K] | | | | +-------+------+------+ +-------|Rs Rtc Ctc | Vcc | | | Vcc | +--|MR Q3 Q4 Q13 | | [75R] | +-------+----+----+---+ [4k7] | | HC4060 | | | | [LED] | +----|----|---[]---+ +---[]--------+ | GND

With the 100k pot adjusted to about mid-scale and Q3 toggling at

1Hz, the LED will flash once every 17 minutes for one second.

The 75 ohm current limiting resistor for the LED is assuming a white LED with a Vf of 3.5V at an If of 20mA.

-- John Fields Professional Circuit Designer

--
Ooops...

That 0.12µF cap needs to be 0.47µF:

   +---------+-----+---------+
   |   Vcc   |     |         |               
[100K]  |    +-->[100k]   [0.47µF]             
   |  [100K]       |         |              
   |    |  +-------+---------+---+                               
   +-------|Rs   Rtc        Ctc  |               Vcc
        |  |                     |         Vcc    |             
        +--|MR    Q3   Q4   Q13  |          |   [75R]        
        |  +-------+----+----+---+        [4k7]   |
        |  HC4060  |    |    |              |   [LED]
        |          +----|----|---[]---+    +---[]--------+                    |
                                                 GND

Yes, it is a video camera hooked to a device that continually looks for sky motion. Probably 1/4 second duration or better would do the trick.

Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA) (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time) Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

--
                     "Predictions are hard to make. Especially
                      about the future. -- Yogi Berra

                     Web Page:

Thanks for the circuit. What is an SCR? I would guess these parts are available from RS. I probably have the cap/res and maybe even the IC. I just responded to someone with the length of the pulse. Probably a 1/4 second or bit longer. Less than 1 second should do. The camera is shielded by a plastic dome about 18" in diameter. I'm not quite sure about brightness. Something that can be seen in the daylight at a distance of about 12" should work. The video camera is attached to a device that detects movement, even a flash. It will run 7/24. I have a red safety flasher about 1.5" in diameter that blinks every second that likely would be detected. It is enclosed in faceted material like that found on the rear light of an auto. Of course, the rate is too high for this use. Small insects crawling across the dome in the day time will trigger the camera detector. (BTW, the device does not download the continuing steam of images unless there is motion. A flash would be considered motion.)

BTW, do you draw these circuits with Word and then convert them to a txt file, or maybe some other tool?

Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA) (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time) Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

--
                     "Predictions are hard to make. Especially
                      about the future. -- Yogi Berra

                     Web Page:

^^^^^^^^^^^^^^^ An SCR is a kind of 'thyristor'. It is a switch in which a triggering pulse will make it turn on, and stay on until current through it drops off to some small amount. Triacs are two way SCRs.

You probably can't get an SCR from radio shack. However, you can replace it with two transistors, an NPN and a PNP, as shown in the prior message.

This circuit can be modified to give longer pulses by using a resistor in series with the LED, and a bigger storage cap. As it is, it'll only give about 2ms of very intense flash. I bet this will be fine, but you never know until you try.

You should experiment to find out.

You might want to ask the manufacturer about how to trigger it on a timely basis, and also why it is stopping unexpectedly.

I use picture-mode in emacs these days. I used to use AACircuits, but that doesn't work very well under linux. If I was using windows on a regular basis, I'd still be using that program, which is quite nice, and easy to use.

--
Regards,
  Bob Monsen

"I cannot persuade myself that a beneficent and omnipotent God would
have designedly created parasitic wasps with the express intention of
their feeding within the living bodies of Caterpillars."
 -- Charles Darwin

--
Oops again...


   +---------+-----+---------+
   |   Vcc   |     |         |               
[100K]  |    +-->[100k]   [0.47µF]             
   |  [100K]       |         |              
   |    |  +-------+---------+---+                               
   +-------|Rs   Rtc        Ctc  |                        Vcc
        |  |                     |         Vcc             |
        +--|MR    Q3   Q4   Q13  |          |            [75R]
        |  +-------+----+----+---+        [3k6]            |
        |  HC4060  |    |    |              |            [LED]
        |          +----|----|---[]---+    +---[]--B 2N4401 
        |                    |                             E
        +---[1N4148>]--------+                             |
                                                          GND

Because of the drops in the diodes connected to the 3.6k resistor,
with either Q3 or Q13 low the bottom of the resistor will go to
about 0.7V plus the Vol of the chip\'s outputs which, without the
diode in series with the transistor\'s base, could keep the
transistor from turning off, leaving the LED on all the time.

...

Google didn't find anything by that name except a forum.

Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA) (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time) Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet

--
                     "Predictions are hard to make. Especially
                      about the future. -- Yogi Berra

                     Web Page:

AAcircuit - no s on the end.

Ed

Emacs is a text editor which uses monospaced fonts, in the traditional unixy way. It enables one to write extensions called 'modes' in lisp, which enhance the capabilities of the editor. Picture-mode is a mode that comes with it. Another mode is cc-mode, which colors, formats, and indents C code.

Emacs is a great editor for programmers, and has lots of cool features.

--
Regards,
  Bob Monsen

"Nothing before had ever made me thoroughly realise, though I had read
various scientific books, that science consists in grouping facts so
that general laws or conclusions may be drawn from them."
 -- Charles Darwin

Sadly, it doesn't work. Here is the real thing:

flow | | e PNP b----. c | | c in-----o----b NPN e | | GND

When 'in' is 0, the NPN is off, causing no flow to the PNP base. When 'in' momentarily spikes, the NPN is turned on, draining current through the PNP's e-b junction, turning it on. That will pull 'in' up (assuming it isn't being held at some voltage), and allow the flow to continue even after the signal is gone. Once the flow abates, nothing keeps the NPN on, so it turns off, awaiting another pulse.

Your circuit can be done as so:

5V-----------[220k]------o---------. | | --- | LED \\ / | --- [100] | | e | 0.1uF PNP b-. --- 100uF c | --- || | c | in--||---o----[100]------o-b NPN | || | e | --- | | / \\ 1N4001 | | --- | | | | | Gnd------o------------------o------'

Where 'in' comes from the timer circuit I posted earlier.

-- Regards, Bob Monsen

"False facts are highly injurious to the progress of science, for they often endure long; but false views, if supported by some evidence, do little harm, for every one takes a salutary pleasure in proving their falseness." -- Charles Darwin