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Flasher?


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Does anyone know a chip I can buy that will make a LED, or light of some kind, flash about 50 miliseconds apart/ give or take. I'm making a wig / wag (flip / flop) circuit and I want to make them strobe like cop cars, alternating. Any help would be great.

Thanks for your time,
Josh

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Hearse,
the first circuit is missing the current limiting resistor for the led.
the second has a bit of a problem...
for the second, i would increase the 220 ohm resistors...maybe to 560 ....
i find the LM3909 unsiutable and expensive for this application. it is good for places where you want to power a led from 1.5V(a single battery)
for this application a 555 is best, or probably a 556 if you want them to flash with 2 different rates. you could also add some transistors and make put together more red leds and more green leds.

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Hearse,
Are you the same guy that was on another post-board requesting that the LEDs flash about 5 times on the left LED then 5 times on the right one, and back and forth like that? This circuit will do that with only 2 CMOS gate chips (4001B or 4011B, or 1 of each):
1) A 2-gate Classic CMOS oscillator with a 10Hz output called FLASH.
2) Another 2-gate Classic CMOS oscillator with a 1Hz output called ALTERNATE.
3) 1 gate drives 1 LED, or parallel 2 gates to get more output power (up to 10V power supply does not need a current limiting resistor).
One input of the gate goes to the FLASH output, and the other input goes to the ALTERNATE output.
4) The other LED is driven by another gate or 2 gates in parallel. One input of the gate goes to the FLASH output, and the other input goes to the inverted ALTERNATE output.
Note that the gate drivers must be the same type of gate.
Connect the unused gate input of a 4001B oscillator to pin7, or the unused gate input of a 4011B oscillator to pin 14.
A 4001B LED driver is active high with the anode of the LED connected to its output and the cathode to pin 7.
A 4011B LED driver is active low with the cathode of the LED connected to its output and the anode to pin 14.
I made a bunch of these flashers for my friends but with output transistors putting 80mA pulses into ultrabright blue or green LEDs.
At night, they can be seen for miles, and work well as a flashlight. A bunch of them shining on the ceiling make cool patterns. The FLASHER oscillator has an additional resistor and diode so that it is ON only 1/4 of the time. I used a low-dropout regulator so that the flashes remain the same until the battery drops to 5V. With only 1 LED flashing 5 times, then a pause, then flashing again, then a pause again etc., a 9V alcaline battery lasts about 24 hours.
I am sorry that I don't have schematic software to post these designs.

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Hearse,
The 4027 will not flip and flop without an oscillator. The oscillator determines the flash rate (number of flashes per second).
Since you need an oscillator, you don't need a flip-flop circuit since the oscillator can drive one LED driver, and an inverted oscillator signal can drive the other LED driver. So the LEDs will alternate.
A single 74C14 Hex Schmitt Trigger Inverter chip (or MC14584B), a capacitor and a resistor will do that. I am not going to design the circuit for you but I will give you some hints:
1) The 1st Schmitt inverter, a capacitor and a resistor is the oscillator. A description of Schmitt triggers (the oscillator is figure 8) is here:
http://www.web-ee.com/primers/files/AN-140.pdf
2) The 2nd Schmitt inverter is the inverter. Connect its input to the output of the oscillator.
3) The 3rd and 4th Schmitt inverters are paralleled on their inputs and are fed from the oscillator. Their outputs are also paralleled and drive the 1st LED (up to 10V supply without a resistor).
4) The 5th and 6th Schmitt inverters are also paralleled on their inputs and are fed from the inverter. Their outputs are also paralleled and drive the other LED as above.
With a 9V battery, the LEDs will alternate with about 18mA of current.

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