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Flashing LED with 555 timer

Former Member

Hello all,

 

I am trying to create a flashing 3 LED circuit with a 9v battery. I want a specific flash time of 20ms and a duty cycle of 1.3 seconds. My question is what size should R1, R2, and C1 be in order to achieve that timing. I found the equations for figuring it out, I was hoping maybe someone would rather take the challenge of giving me the answer instead of me going back to school to relearn algebra. Any help is very much appreciated.

 

Thanks.

  • 0

    Mr. John,

    Thank you you for the video. I have tried the same on my Arduino Uno. I guess I should go into more detail as to why I am trying to achieve this effect and on what platform. During my time in the military we used IR strobes in order to ID one another on the ground at night. Through night vision goggles these things are super bright. I actually still have two of them hidden somewhere in my house. One has two probes sticking out that you make contact with them with something conductive to program different flashes The other more simple is set on a fixed time. I can't find them. Here is a link to the exact strobes among others that we used.

    https://www.cejayengineering.com/Buy-Online/IR-Strobes-Beacons/902111IR.html

    I Wanted to try and recreate the circuit in order to use different color LEDs and to learn more about the 555. Every circuit I come up with looks more like a dim light blinking instead of the bright strobe effect that these small strobes produce. I tried to find the ones that I have in order to see what was inside but have had no luck finding them. I looked at there website to see the data sheet and all it really gives is the timing of it. So that's why I have been shooting for that particular timing. If I can figure it out i want to get a bunch of boards printed so that I can make different colors and give them to all the kids in my family. Just something neat to play with and drive there parents crazy. Plus I have a bit of kid left in me as well. I just wanted to see how hard/easy cheap or expensive that I could build them for really.

  • 0 in reply to Former Member

    Hi Rob, Thanks for the insight into your project. This is off subject but showed me a while ago that one can see the infrared LEDs using a camera on a cell phone or other camera. Try it with your TV remote control. I will let you know if I can come up with any other simple circuits.

    John

  • 0

    Hi John, I'll have you know that on the morning of the Packer's victory over the Cowboys, I had Kielbasa con chilaquiles for breakfast in support of their effort.  They were tasty, I admit.  I'm sure it helped.

     

    The timing method you illustrate here will only work in environments that are bare-metal, no interrupts or thread-locked.  Here are some early efforts to decouple timing from the cpu:

     

    http://www.z80.info/zip/z80ctc.pdf

     

    http://liris.cnrs.fr/~mmrissa/lib/exe/fetch.php?media=mc6840.pdf

     

    'course this stuff is integrated into the modern controller.  MSP430 has a good price-point and is replete with timing hardware.

  • 0 in reply to D_Hersey

    Hi Don, The Packers and all my fellow cheese heads thank you for your support. I haven't seen much mention of the Z-80 since I sold and serviced Radio Shack TRS-80 computers back in the 80s. Also thank you for not mentioning my blunder in writing uS when I meant mS in my post. Yes the circuit I put together is not good for much else than just blinking the LEDs.

    John

  • 0

    Hi Rob,

     

    I don't know if you keep on wanting to try it with 555.

    If yes, try this sch.

    image

     

    See some rude calculations:

    image

    image

     

    But I am not sure if it is posible for the human eye seeing so short pulse, try it.

     

    Also take into account that timing may vary depending on the resistors and capacitor tolerance, if you are looking for accuracy just use microcontrollers as our colleagues suggest.

     

    Hope that helps,

    Miguel

  • 0 in reply to gihu

    Hi Gihu,

    For the fun I bread boarded your circuit and it seems to work just as you predicted. I couldn't quite get to the 18 meg value of Ra so it was flashing a little more often than 1.3 seconds. I ran the Vcc at 9 volts and used an NTE 29 equivalent for the output transistor. The duration of the pulse is not a problem for the human eye which can detect even one photon under proper circumstances. The problem is as soon as the pulse gets shorter than about 70 mS the eye continues to interpret the pulse as being 70 mS. This is because of the residual image effect of the photoreceptors in the eye. Here is a photo of my circuit.

    Rob should be able to use your design to do what he wants and the values that you have calculated are very close. I did not put the scope on them but from what I gather he may not be that critical for his application.

    John

     

    image