# Need help understanding this circuit

#### SparkyCal

Mar 11, 2020
846
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?

Thank-you!

#### bertus

Moderator
Nov 8, 2019
2,851
Hello,

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

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.

Bertus

Last edited:

#### Ylli

Jun 19, 2018
383
It calls for a capacitor that is 470 nF. I don't have one. I have 47 UF. Is that the same?
470 nF = 0.47 uF

#### SparkyCal

Mar 11, 2020
846
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?

Thank-you

#### Bluejets

Oct 5, 2014
6,187
I am still not clear however. Do pins 1, 2 , 3 and 4 on the IC55 get connected to one another?

No.
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.

#### Audioguru

Sep 24, 2016
3,650
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.

#### AnalogKid

Jun 10, 2015
2,698
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.

ak

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#### SparkyCal

Mar 11, 2020
846
Thanks for all the tips and advice,. It is helping.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,508
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

#### Audioguru

Sep 24, 2016
3,650
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
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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