I'm building a Revell Enterprise Into Darkness model with LEDs and I need help with circuit that makes two fast flashes, pauses for 3 seconds, then repeats. as seen in the movie. I have searched and found circuits with constant flashes but can't find the one I need (2 flashes, 3s pause, repeat).
closed as too broad by Dave Tweed♦ May 24 at 22:09
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There are a couple of basic approaches you can take for your project.
Per your question title, you are looking at 555 timers and a 4017 decade counter. Without going into detail on the circuit, let's do a thought experiment to consider how you might utilize the output of the 4017: Two pins for the "flashes", and the remaining eight pins for the delay. Except there would be no "off time" between the first two outputs, which wouldn't produce the desired two flashes. So you'd have to instead use the first output for the first flash, and the third pin for the second flash, and the remaining seven pins for the delay.
Let's do a quick calculation. If the seven pins equate to 3 seconds, then each pin change would be ~430 ms. The flashes would therefore be approximately a half-second on with a half-second off in between. My experience with the famous Enterprise ship (I admit I'm a Trek fan, too) tells me that the flashes are a good deal faster than that.
If you're after something cheap and basic, this could work, but the flash time and off time are intrinsically related.
A much more configurable approach, albeit more expensive, would be to use a microcontroller. The most accessible entry point would be to use an Arduino or compatible cousin, for which there is a lot of support (including the Arduino StackExchange site). With this, you can write a program to control the state of the output pin driving the LED (or transistors depending on other factors). This allows for a great deal of control over the timing, potentially lower component count, and simpler troubleshooting.
Personally, having built a fair number of Star Trek prop lighting circuits... I'd use a little Atmel (now Microchip) ATTiny13.
In both cases, you'll need to consider or determine your power source, current limiting for the LEDs, transistors (in case the LEDs require more current than the IC can handle), etc.
There are a lot of other questions here about driving LEDs with microcontrollers, so be sure to check those. Good luck with your project.