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Need help understanding this circuit

Discussion in 'General Electronics Discussion' started by SparkyCal, Apr 2, 2020.

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  1. SparkyCal


    Mar 11, 2020
    I am hoping you can assist with my interpretation of the circuit I have linked to below. More specifically, I am building the circuit found at at 8:00 mark in the video (it is called the Sound Generator)

    Here are my questions.

    1. It looks as though he is soldering the first 4 pins on the IC555 together. When I look at underneath the circuit board, he shows a straight line of solder connecting the pins. Does that mean that pins 1-4 of the IC55 are now making one single connection. In other words, are all 4 pins connected together? That would seem strange to me. I am trying to build this on a breadboard, so I need to know if I need to find a way to connect those pins together.

    2. It calls for a capacitor that is 470 nF. I don't have one. I have 47 UF. Is that the same? I have a capacitor marked 10. Can I use that?

  2. bertus

    bertus Moderator

    Nov 8, 2019

    It would have been nice if you posted the schematic in stead of the youtube.
    I have extracted the schematic:

    Sound generator.png

    The 22uF determined the modulation speed, as it is connected to pin 5 of the second 555 and the 470 nF determined the tone frequency.

    Last edited: Apr 2, 2020
  3. Ylli


    Jun 19, 2018
    470 nF = 0.47 uF
    Cannonball and davenn like this.
  4. SparkyCal


    Mar 11, 2020
    Thank-you and sorry about the schematic. I did not think to do that, but will in the future,

    I am still not clear however. Do pins 1, 2 , 3 and 4 on the IC55 get connected to one another?

    I don't have a .47uF capacitor. i have a set of capacitors and some of them say 47uF 10V FW but that is not the same as .47 right? If not, what other capacitor values can I swap in?

  5. Bluejets


    Oct 5, 2014
    If you look closely at the video you will see the "span of the pins" is 4 holes wide.
    What appears to be (from your point of view) a short is actually the bridge line from pin 8 to pin 4.
    The pins 5 to 8 are one space further over.
  6. Audioguru


    Sep 24, 2016
    With a 9V supply and an 8 ohm speaker connected directly to the output of an LM555 or NE555 then the current will be so high that the 555 will burn out. But it will be OK if an ordinary 9V battery is used because that little battery will not be able to provide enough current to do damage.
  7. bertus

    bertus Moderator

    Nov 8, 2019
    davenn and Harald Kapp like this.
  8. AnalogKid


    Jun 10, 2015
    The two rows of pins in an 8-pin DIP (dual-inline package) are 0.3" apart. That means that with the perf-board he is using, there are two rows if unused holes (with copper pads around each one) between the rows of pins. Rather than run a wire from pin 1 to pin 8, he is using globs of solder to bridge the gaps between some of the pads to form a zig-zag connection path.

    Like using the handle of a screw driver as a hammer, it is a trick that can get you out of a jam. But it is lazy and sloppy technique, completely unnecessary if you have a supply of wire and the whole 1 minute it takes to strip the two ends and solder it in place. To me it is an indicator of the abilities of the instructor and the quality of his information.

    A shortcut is like a rule of thumb - the most important thing to know about them is when *not* to use them.

    Last edited: Apr 3, 2020
  9. bertus

    bertus Moderator

    Nov 8, 2019
  10. SparkyCal


    Mar 11, 2020
    Thanks for all the tips and advice,. It is helping.
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    He appears to be using a high impedance piezoelectric transducer, not an 8Ω speaker.

    Also he doesn't i clearly indicate which way around polarised components go.

    He has all that extra length of component leads, yet seems to do the dodgy linking of pads together.

    These "top 'n' electronics project" videos are not a way to learn electronics.

    And OMG mains writing !!!!!! Aaaaagh
    Bluejets likes this.
  12. Audioguru


    Sep 24, 2016
    The video (from India?) shows an 8 ohm speaker at 8:00 in the video not working because the 555 ICs are not powered.
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