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Simple 555 synth idea

Yoa01

Jun 18, 2012
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Hey guys,

So I know I have not been on here in a while, but that's no matter. What is the matter is I have this idea to build a simple square wave synth using a 555.

It uses a 9v battery to power the NE555P, which has two pots which control pitch and I think pulsewidth (just using my limited knowledge of analogue electronics). Then, it goes into a simple RC low-pass filter, with a pot as the resistor. That then outputs to a speaker OR a jack, depending if there is a plug in the jack or not.
555synth.png
My main question is, will this work? I mean, I'm pretty sure it will, my only concern is the filter really.

Secondary question: I recently got a small microphone, is there a way I can combine that with the 555 so that, say, if I were to talk into it, it would be somewhat intelligible? I was thinking a ring modulator or some other simple thing. What do you think? I'd probably put an input jack as well as a mic.
 

davenn

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hi Yoa

good to see you active on here again :)

just an initial observation .... when you do a drawing a few things

1) number the pins of the chip
2) connect pins of the chip to where thay should go eg the GND pin you should have it going to a GND symbol ....
else everying will ask the obvious .... " did you remember to connect the GND to the chip ?"

3) Dont draw components over the top of the chip/other components
4) you have named 2 x resistors as pots ... are they really just resistors as the symbol shows or are they pots drawn incorrectly ?
.... that is ... do you really want to have those 2 resistors adjustable ?

Dave
 

CDRIVE

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I don't think you're going to produce much speaker audio when feeding it through a 100K resistor or Pot. That 10uF cap is also going to swamp out audio. Also, your jack isn't drawn correctly. There should be a speaker disconnect contact.

Chris
 

Yoa01

Jun 18, 2012
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I'm still new to drawing stuff, sorry.
Is numbering pins better than showing what they actually do?
I totally forgot to draw in the ground, though I would have connected it.
I only drew that pot over the IC because I wanted to draw the diagram in the layout the 555 is laid out, just to make more sense to me while building it.
And I was kinda hoping that saying 'Pot' would suffice for drawing the potentiometer symbol :)

I will probably have to install a somewhat hefty amp, then? Or just lessen the values? I wasn't entirely sure what values to have there, but I knew it wouldn't be the best choice. I was thinking, since the speaker I have is small, I'd probably use the main output to an external amp anyway. And yeah, I know about the jack. After I posted this I added a few things and fixed the jack. I'll fix everything else and repost later today (don't quite have the time to redraw at the moment, sorry!)
 

Raven Luni

Oct 15, 2011
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A single transistor should be enough to drive a small speaker
 

Harald Kapp

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If you leave out the resistor and capacitor at the output of the 555 you can drive a small speaker directly. Otherwise a simple common emitter transistor amplifier is good for driving a mediu size speaker.
 

Yoa01

Jun 18, 2012
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The resistor (actually a pot, working on it) is part of a simple low-pass filter, it's not just something I thought I needed to drive the speaker. I should have labelled.

However, I did. Well, now, anyway. Here is the updated schematic (don't mind the stuff at the bottom, that's not finished yet)
555synth.png
I added labels so that you know what things are, though I feel as if I should have also segmented the different sections.

I took the advice of laying things out on a single plane (no overlapping components), grounded the 555 (oops), drew actual potentiometer symbols where they go, and added a distortion circuit (at least, I'm pretty sure that's what it'll do) and input section (which has both a mic and a 1/4" switched jack). Finally, I am working on figuring out how to wire the ring modulator section (the bottom setup).

Note on the input section: it will be able to be the modulator for the ringmod, or routed to the distortion, or routed to the filter. This is very much like the 555 oscillator, which can be the ringmod's carrier, or routed to the distortion circuit, or routed to the filter.

I did attempt to draw the switched jack correctly, but I'm pretty sure if that was an actual jack it wouldn't do squat. We'll just say that it's a switched jack until I learn how to actually draw one.

I also don't know preceisely what ohmage pot to use on the filter, nor the capacitor type. Any help would be greatly appreciated. And yes, just to reiterate, the pot/capacitor setup is a simple non-resonant low-pass filter, not a driver or an audio swamper (well, kinda).

Yours in Music,
Yoa
 

CDRIVE

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Regarding your updated schematic... No. What part of it? Just about all of it. How can we make sense of it? It has dead ended lines and a host of issues to numerous to mention. I suggest that you post what you want and have a member design it for you.

Chris
 
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Yoa01

Jun 18, 2012
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I quote: "don't mind the stuff at the bottom, that's not finished yet" If the open wires you are referring to are the diodes, switches, and other wires at the bottom, there's your answer.

I wouldn't be asking for advice if I were to have someone else design it, would I? How else does one learn? It's bound to have numerous issues, just like anything one is just learning. And yes, I know my drawing is sloppy, but you can still follow the connections. But I did forget a 100k pot in there, I'll be sure to draw that in.

Also, consider this: like many people on this forum, I base my ideas and schematics off of ones I've found. Here I found the 555 oscillator idea, found the distortion circuit, found and used the ring mod not finished), found and used the filter, and found and used the input and output sections. If things don't add up, it's because they are from differing sources and I an still new at this.

I apologise for my noobiness.
 

CDRIVE

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(1) When conductors cross paths on a schematic we don't know if the junction is connected unless it has a dot.
(2) Your transistor has a 10K collector resistor. It will not drive a 4R, 8R or 32R speaker. A 32R speaker connected through a 450uF cap directly to the output of the 555 will drive it better. I would not connect the speaker directly to the 555 though.

The microphone will not drive the speaker either.

Chris
 

CDRIVE

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I just noticed that the collector signal is shorted to ground. I also see that you're not trying to drive the speaker directly from the mic as I thought in my last post but it's still not going to work as wired.

Chris
 

davenn

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Hi Yoa

here's a copy of your circuit showing some of the errors .... its not really to make it work... its more for you to learn and understand some of the ways you went wrong OK? :)
I appreciate you want to do this yourself but you really need some serious help


attachment.php



it would really help ...as Chris said, to tell us exactly what you are trying to achieve with this cct and maybe we can help you better to make it work :)

Looking at some 555 timer datasheets will give you lots of basic circuit ideas which will also help you along your way

we are here to help, keep trying :)

cheers
Dave
 

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CDRIVE

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it would really help ...as Chris said, to tell us exactly what you are trying to achieve with this cct and maybe we can help you better to make it work :)

we are here to help, keep trying :)

cheers
Dave

Dave, oddly enough this topic was started here, where the schematics were much easier to follow and coherent. Perhaps we should point him to LTSpice or Tina-TI for his schematic drawing.

https://www.electronicspoint.com/building-ring-modulator-t250299.html

Chris
 

davenn

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Dave, oddly enough this topic was started here, where the schematics were much easier to follow and coherent. Perhaps we should point him to LTSpice or Tina-TI for his schematic drawing.

https://www.electronicspoint.com/building-ring-modulator-t250299.html

Chris

yeah ... primarily cuz they werent schematics he drew ;)

As long as Yoa is willing to learn and takes on board what he is being taught ( unlike some you see on the forums) I'm, and Im sure others, are always happy to help and encourage those willing to learn :)

Personally I have never used any sim programs, both those you mentioned are supposed to be respectable and cover the majority of situations

Dave
 

Yoa01

Jun 18, 2012
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Chris:

Sorry, I've almost always seen (probably amateur) schematics drawn like this, and where they don't cross one wire is curved, which is what I did here.

What would be a better choice for a resistor? And what do 4R and such mean for speakers? Should I simply leave the speaker out and just use an output jack to an external amp?

I assumed I should add an amp to the mic :/

Dave:

Thank you! Just a few notes, though:

-One of the two wires going to the Trig pin should have a pot on it as well, I forgot to add it back when I moved it.
-The 100k pot, if I remember correctly, is used to regulate input volume. Could be wrong.
-I cannot remove the 100k pot at the end because that (presumably) regulates the cutoff frequency (it's supposed to be a simple RC low-pass filter)

Chris (again): for this I was using MS Paint (not exactly the best, I realise), but I do have and sometimes use DipTrace if that would be easier to comprehend.



As for what I am trying to do here, it's pretty simple (well, so I thought): build a neat, small synthesizer. I want to use the 555 as a square wave oscillator with frequency (and preferably pulse width) controls. That goes into a low pass filter, which goes to an output.

As for other stuff I want in it: external input, ringmod, and distortion. The ringmod and distortion are switchable for both the 555 and external input. Here's a picture:
noob.png
This shows each part and their switching (like patching, but... not). The oscillator can be patched into the ringmod, then back out to the filter OR the distortion, which automatically goes to the filter. The input can go to the ringmod or distortion, or just straight into the filter. Either way, everything goes through the filter, then the output.

Believe me, I am more than willing to learn. If I make a mistake (which I do), I want you guys to tell me. It's like music: if your first song or album is crap, you'll want people to tell you why.
 

CDRIVE

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4R is just another method of writing 4 Ohms or 4Ω. ;)

Let's start with your schematics first. I've used LT Spice but I like Tina better. I can build a circuit in less that a tenth of the time it takes me in LT Spice.
http://www.ti.com/tool/tina-ti

If you're going to use a 100K + cap RC filter you will have to drive the input of an amp from it. You can't directly drive a speaker from that RC network. An OPA134 is an excellent low noise OpAmp.

Chris
 

Yoa01

Jun 18, 2012
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Ah. Thanks.

Heh, I just read the Readme after installing and it says to not use it for educational purposes. Oh well...

Alrighty, I'll look into that. Thank you!
 

akida

Oct 4, 2012
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Chris:

Sorry, I've almost always seen (probably amateur) schematics drawn like this, and where they don't cross one wire is curved, which is what I did here.

Hi Yoa01,

You're not crazy! As an electrician in Australia we use this method when we draw circuit diagrams. However, I am not an electronics specialist and I can only imagine how complex a electronics circuit diagram can be. The method that they these guys are using seems to be more efficient. :)

Happy drawing!
 

davenn

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...............................
Chris (again): for this I was using MS Paint (not exactly the best, I realise), but I do have and sometimes use DipTrace if that would be easier to comprehend.

Hi Yoa

Actually MS paint is awesome for circuit drawing, and have done examples of my work on here often showing how good you can do diagrams :)
MAKE sure you click on the yellow bar above the image to see it at full size and to see how sharp and clear it is
here's a couple of additional examples.......

attachment.php


attachment.php



OK ....
Rule 1) DONT use colours and low resolution. Use monochrome bmp as I have done

Rule 2) Lay the schematic out systematically .... that is ... inputs on the left, outputs on the right power supplies on the left, and this applies to all cct diagrams regardless of if the are drawn by hand or on a computer

Rule 3) positive voltage rails along the top, negative rails along the bottom. and where possible everything else in between those 2 lines

Rule 4) when you save the bitmap, it will usually be ~ 100 kb for a full screen size 1024 x 768. once saved, you can then do another save as a GIF file for posting to forums etc.
the equivilent GIF file will be less than 20kb in size and ideal for uploadinging and easy and quick for people to download. Those 2 I posted are only 7.6 kb and 8.5kb ibn size

Rule 5) and this is a goodie, it makes drawing the circuit much easier....
when you draw a chip say your 555 timer, you dont have to have the pins around the chip image in their correct order
have a look at these examples of mine.....

attachment.php


note how the the output pin, pin 3 is on the right side, the 2 power connection pins 8 and 4 are at the top and the GND pin, pin7 is at the bottom. This is all standard convention :)

You are welcome to save copies of those pics of mine and use the component symbols in your own drawings :)

cheers
Dave
 

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Yoa01

Jun 18, 2012
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I knew you people were incredibly helpful the moment I joined this forum. THANK YOU!! And yes, I will 'steal' your diagrams :)

- No colours, got it.
- Hey, at least I did follow rule #2!
- Ok, + on top, - on bottom. I can remember that.
- Could I just save it as a GIF to begin with? I know 100k is small, but I am somewhat strapped for HDD space.
- Honestly, I only drew out the 555 like that so that it would be easier for me to assemble it, but seeing as how it's totally messed up I may as well do it the right way.

Also, with ICs, I should draw out both pin function and number? Or does that even matter?
 
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