Why won't this stupid drawdio work?

[Jakobberry]

Hi!

I'm completly new to electronics and I wanted something simple to make. I've tried a couple of different drawdio schematics, but I can't get any of them to work.
I must have missed something.
I wanted to make the drawdio from this page
s-lab Drawdio
I took some pictures of what I made. I know it's probably not pretty, but as I said I'm completely new to this.
Please help!

Front **broken link removed**
Back **broken link removed**

 

[Jakobberry]

Well I figured out that I put the speaker+ wire in the wrong place. But I fixed it and it still doesn't work.

 

[mneary]

The picture shows every little thread in the left side of the board. I only have one monitor and it is a mere 1280 pixels wide.

 

[Jakobberry]

Is that better?

 

[AllVol]

Hard to tell, but it appears you may have forgotten to remove the trace beneath the large electrolytic cap.

 

[Jakobberry]

No, the cap connects to the track below. The speaker wire is connected wrong on the picture. It's connected to the track below now.

 

[DirtyLude]

Based on what I can figure out from what you said with the wire correction and what I can make out from the picture the one thing I can see is you polarized cap is backwards. The negative side should be towards the speaker.

EDIT: Funny, the schematic shows the polarized cap the way you have it, but the picture of the breadboard sample shows it the other way. I have no idea.

 

[audioguru]

The piezo transducer is a capacitor so the output capacitor is needed only for a coil and magnet speaker.

 

[transistor495]

One error is cap polarity as DirtyLude pointed out. + pole goes to 3rd pin and -pole goes to speaker+.

This is just a 555 based metronome configuration as you can see on the image below:
**broken link removed**
The component values are varied here. Note that in place of 1K(this pic), you have 100K in your circuit between pin no. 6 and 7. The first debugging will be to get a standalone metronome by shorting the 'out to graphite' and 'out to foil' leads. Once you get the noise through speaker, you can re-arrange it for use with graphite pencil.

 

[audioguru]

I think the "681pF" capacitor value is too low and will result in a frequency that is so high that it might not be audible. Try a 0.0022uf to 0.01uF capacitor instead then short the two leads of the pencil together.

Maybe some pencils today do not use conductive carbon (graphite).

 

[Jakobberry]

Thanks. For all the input. I tried reversing the cap, but it still doesn't work. When I connect the battery I get a little static sound, but only at the moment I connect it, then it's gone again. It does this no matter which way the cap is.

I'm gonna have a closer look at the metronome.

All the drawdio schematics I've seen use the 680pF cap, so I'm not sure that's an issue. I haven't mounted it on a pencil yet, so the lead touching is how I test it.

 

[transistor495]

Seems like it goes in ultrasonic region .
Try decreasing the value of 100K or increasing the 681pf. This is such a simple circuit that you should get the tone by just varying the component values.

Is the battery new?

 

[Jakobberry]

I tried changing the 100K to a 1K. No difference. The battery isn't new. It's down to about 8v, but that should be more than enough to power this thing.

 

[audioguru]

I tried changing the 100K to a 1K. No difference.

Then the frequency will be as high as radio waves.
Is your capacitor "681pF"? Then change it to 2200pF (0.0022uF) or to 0.01uF and short the wires together that go to the pencil. It should make a tone in the speaker.

 

[transistor495]

As I calculated, it should be around 10KHz tone when correct values are used. On closed view, I can't find anything wrong on your assembly except output cap connection(seems something wrong there..).
JRC-555D can be failed when you connected the speaker directly to pin-3. I'm sure that by replacing it with LM555+fresh battery you'll get into the right way

 

[audioguru]

As I calculated, it should be around 10KHz tone when correct values are used.

Many people think an FM radio sounds the same as an AM radio because they can't hear anything above 3.3kHz. Then they won't hear 10kHz. Many speakers can't produce frequencies as high as 10kHz.

 

[Jakobberry]

Thanks for all the great advice. I'm gonna give it a try.

 

[Jakobberry]

Ok. I put in a 0.01 uf cap and I have the 100K resistor in, a new jrc-555d and a new battery. I have sound. But it is a very high pitched sound. And it's there without the leads touching. Nothing changes when I touch the leads together.

 

[Jakobberry]

I tried a couple of different values on the cap. It's pretty cool seeing what the change in value does to the sound. I'm gonna have to buy a breadboard tomorrow. That'll probably make it easier to figure out. I still have the problem with the sound being there without the leads touching. I've checked the connections. Can't see what's making it do that.

 

[mneary]

Something is shorting the 'to graphite' lead to 'gnd'. Check and double check that there are no tiny pieces of copper or contaminants (solder flux, etc.) in or near where the traces are cut. [edit] Also try to find something between 'to graphite' and pin 3. [/edit]

Thanks for the better pic, by the way.