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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).

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closed as too broad by Dave Tweed May 24 at 22:09

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Hi BlazZz, you need to be aware that the site isn't about asking for a schematic to accomplish an overall task. Instead you'll need to ask specifics about aspects of your electronics design goal. It appears from the title you are wondering whether to use a 555 timer or a 4017 CMOS decade counter. You do have a specific outcome explained in the question, but unfortunately there is no "connection" between these things. Are you at all experienced with circuit design? Have you considered using a small microcontroller? \$\endgroup\$ – JYelton May 24 at 21:21
  • \$\begingroup\$ Probably the easiest way (as JYelton) says is to use a microcontroller, if no or very less experience, use an Arduino Uno (or if you need something smaller: Nano/Micro). Cost (much) more than a 555 and some components, but it's more flexible. \$\endgroup\$ – Michel Keijzers May 24 at 21:27
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    \$\begingroup\$ A 555 can provide the clock for a 4017, if you set the period to be \$300\:\text{mS}\$. Use the rising edge of pin 2 and pin 4, for example, to trigger a short LED flash -- giving two quick pulses separated by \$300\:\text{mS}\$ ("fast flashes.") It will take \$3\:\text{s}\$ to cycle around. You can also just AND the clock with pin 2 and with pin 4 and OR those results to drive the LED, I suppose. (You can choose other pins. I just zeroed in on those two because I felt like it.) \$\endgroup\$ – jonk May 24 at 21:33
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There are a couple of basic approaches you can take for your project.

  1. 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.

  2. 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.

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  • \$\begingroup\$ crazy but true: if you leave the 4017 VCC unconnected the first two outputs will give flashes \$\endgroup\$ – Jasen May 25 at 0:18

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