Star Trek Red Alert Sound Effect (using 555 Timers)

My family went on a Star Trek kick recently and I was trying to make something related so I made this to simulate the Star Trek red alert.

First I looked online to find a circuit diagram but I couldn't find any working projects that didn't use an audio recording module. (which doesn't count!)

So I had to make my own that sounded fairly authentic, (by which I mean that I listened to the red alert in videos while adjusting the circuit) and I think I succeeded!

Step 1: Materials

The things you will need to build this are as follows:

• Power supply 5V - 15V
• Breadboard
• 555 timers x 2
• PNP transistor (BJT)
• NPN transistor (BJT)
• Red LED
• Diode
• Select switch
• Speaker

Resistors

• 10KΩ x 4
• 1KΩ x 4
• 330Ω
• 33Ω
• 10KΩ potentiometer x 2

Capacitors

• 100nF x 5
• 47µF
• 100µF x 2
• A bypass capacitor is recommended

A voltmeter is not required but may help with circuit debug.

Step 2: Making It

(Thanks to user bricomario for the new schematic picture! I had an old one I drew in fritzing that wasn't nearly as nice.)

Put the parts together as in the schematic above.

Then you will need to adjust the potentiometers until you find the right frequency, for me that was at 1/3 of the rotation and 2/3 of the rotation respectively.

Step 3: Theory

Now here comes the theory, if you are too scared (of theory) or already understand how it works then you can be finished!

First you need to understand the 555 timer.

The first 555 timer is an astable multi-vibrator that is controlled by the voltage from the switch, when the voltage is high then it operates normally, but when the voltage is low it inhibits the operation of the 555 using the reset pin.

Then when the output of the 555 goes high it charges the capacitors through the diode, which as they discharge slowly through the 10KΩ resistor (labeled R4) they create the changing tone you hear.

When the first 555 is high then the second is inhibited, but when it goes low the second is enabled to create the tones determined by the capacitor's charge level.

Now use your voltmeter to measure the voltage at the base of the PNP transistor, as the LED flashes you should be able to see the change in the voltage.

Now put your meter's leads in series with the speaker and measure the current through the speaker.

Comments

[sfbaynate]

Hi!
This is exactly what I'm looking for but I'm a little confused about the capacitor values. Can someone post the correct values and if they are electrolytic or not? I think this is what they are.

C3 is 47uf electrolytic
C1 & C4 are 100uf ceramic. (They are shown as electrolytic on the schematic)
C2, C5, C6, C7 are .1uf or 100nf ceramic.


Thanks!

[bricomario]

Hi Transistors, thanks to show my schematic but can you please change it for the one titled « red alert final...2022-11-24 » (on a previous comment) as it showed the good capacitors C1 and C4 with values of 100µF. It works well with those values. Thanks.

[bricomario]

Hi Transistors, I have made your schematic on KiCad for more uniformity with others I have. If you want to chek it and use it, go !. Soon, I will make the breadboard test and ideally a PCB.

[transistors]

Nice! That looks a lot better than the one I made. I'll definitely use it. :D

[bricomario]

Hi transistors, there were a double information about C1 and C4 polarised capacitors : on the schematic 0.1µF and on the material's list 100µF... The good one is both 100µF. And the sound is perfect !! Here is the pdf of the revised schematic on KiCad. My video size of the circuit was too big to upload. Thanks to have published this Instructables !

[bricomario]

Trying to upload the pdf of the schematic...

[bricomario]

I'm glad you used it. When you're talking about 10KΩ resistor (labeled R7), you're talking about R4 in my schematic, right ?

[transistors]

Yeah, that's the one.

[bricomario]

Ok, thanks. I'm working on it... but no sound, no led flashing so far. I have to learn now how to calculate values and how to test with multimeter and oscilloscope at different points on the schematic. Hope the KiCad schematic is like the first you did !

[bricomario]

Hi Transistors, just to mention that the link 555 timer « first, you need to understand the 555 timer » is not working. As you explain things clearly, it would be nice to learn about this 555 timer. Have a nice day.

[transistors]

Fixed. :)

[bricomario]

Transistors, the link works but it is a bit hard to read because the format ; here is a link to the same content but as a pdf : 555_tutorial_tony-van-roon.pdf

[bricomario]

Thanks :)

[Brian L]

Hi
Having trouble getting the circuit to work properly. What transistors did you use for Q2 and Q3?

[transistors]

Hi Brian.
Hi I used 2N3904 for my NPN transistor and 2N3906 for my PNP transistor. However, as these transistors are being used as switches and not as amplifiers (and are pretty generic) I don't think that it matters what transistor you use.

[bricomario]

Very nice project and exact sound ! Please, what are the transistor you are using, NPN (like 2N2222) and PNP (like 2N3906) ?

[transistors]

Hi bricomario.
I used 2N3904 for my NPN transistor and 2N3906 for my PNP transistor. However, as these transistors are being used as switches and not as amplifiers (and are pretty generic) I don't think that it matters what transistor you use.

[bricomario]

Hi Transistors, thanks for your fast answer !

[starbase101.]

It would have been great if the demonstration video included adjustments to the sound frequency, because the pitch in the video is too high compared to the actual sound effect and I would have liked to hear the sound at a slightly lower frequency before investing the resources and time to build one.

[Luiz AntonioV]

Sir, I think you forgot put your name. Anyway I'd like to talk you. I have been working in a private personal project and I choise your alarme project to include in this project. Could you send me your e-mail to talk about it. My personal e-mail is [e-mail] and my website is www.vargasp.com Congratulations and Best Regards