Drawdio low sound

[bigboss59400]

Hello,

Thanks to your schematic, I made on stripboard your drawdio (V2) however when I powered it up it works but it was very low so I change my 1 AAA batterie to a li-ion (1cell) but it didn't change.

Have you got an idea ?
If you want some picture I can but it will not be clean

Thanks

[adafruit_support_mike]

Are you using 'low' to mean 'not loud' or 'bass'? Both are possible, and have different causes.

A couple of pictures will help. Top and bottom views of the board will let us see what components you used and how they're connected. Don't worry about whether it's pretty.. very few "hmm.. I want to try that" circuits are.

[bigboss59400]

Helo,

Thanks for your reply, what I mean by low is we can hear something but it's very hard and not I'm not deaf ;p.
For the schematic like I said before I used the V2 of drawdio schematic : http://www.ladyada.net/make/drawdio/drawdio2schem.png
For the list of component I used exactly this one (for the V2 of course) : http://www.ladyada.net/make/drawdio/parts.html
For Q1 I used PN2907 for R1 I used 20 MEGAohm resistor

Here's some pics (but like I said it's not clean) :http://img10.imageshack.us/slideshow/webplayer.php?id=img0100ed.jpg

I have a multimeter and I can have access to an oscilloscope 2 times by week. I'm not a beginner but I don't know what to test to detect the problem ;(.

Thanks a lot

[adafruit_support_mike]

Ah.. air-wiring SMT chips. That's always fun.

Quick suggestion: see if you can find some 28-30 gauge magnet wire.. the kind that looks like bare wire but has a thin layer of insulation baked on. It's *much* easier to work with than multi-strand wire when you build circuits this way.. especially when you're working in tight spaces.

The circuit looks more or less okay. I wasn't able to trace all the connections from the photos, but could follow enough to get the general idea. Do double-check all your pin connections to the IC.. it's amazing how easy it is to get those mixed up when they're floating in midair.

If you're getting any buzz at all from the speaker, it means the 555 oscillator is probably working, which is a good start. Just to be sure though, put it on the 'scope and check each of the pins. Pins 1 & 4 should be VCC, pin 8 should be GND and pin 5 should be 2/3 VCC. Pins 2 and 6 should show an RC charge/discharge signal running between 1/3 VCC and 2/3 VCC. Pin 7 should show a square wave between VCC and GND, and pin3 should show a square wave between VCC and VCC - .65v .

If the oscillator is working and you just aren't getting power to the speaker, there are three places I'd look: the speaker itself, the transistor, and pin 3 of the 555.

First, make sure the speaker's impedance is really 8 ohms. I couldn't see enough of it in the photos to know if that information was printed on the back. If it isn't, measure the coil resistance with an ohmmeter.. the DC resistance will be a little less than the AC impedance, but it should still come out in the 6-7 ohm range. Check the signal from the SPK+ side of the speaker just to find out what's actually happening there. From your description, I'd expect to see a low-amplitude square wave.

Second, double-check your datasheet to make sure the transistor is connected right. I'm pretty sure it is, but again, it's easy to get confused. The emitter should be tied to VCC, the collector should be tied to R2 and C2, and the base should be connected to pin3 of the 555. Check the signals at the base and collector to make sure those are right.. the base should show the same signal as pin 3, and the collector should show a square wave between GND and VCC with the opposite phase (when the base goes high, the collector goes low, and vice versa).

If the signal at the collector doesn't go from GND to VCC, it means you aren't getting enough current through the transistor, probably because the transistor can't send enough current to pin 3 of the IC. Check the datasheet for the exact chip you used and see how much current it can sink through pin 3.

If none of that leads to a solution, hopefully the information from the 'scope will give us a better idea of where to look next.

[bigboss59400]

hello,

Thanks for your (big) reply but I have checked the transistor and the transistor was inverted maybe I haven't checked enough
So now that's work great (with a li-ion cell) however I need to put some water on paper even if it's doesn't works I used a 20M ohm resistor should I change it by a 10 ? (I speak for R1)

Sorry about waste your time but I think if someone have a problem it could check on your post and see what to do...

Thanks again for all your help.

[adafruit_support_mike]

Thanks for your (big) reply but I have checked the transistor and the transistor was inverted

That will do it.

So now that's work great (with a li-ion cell) however I need to put some water on paper even if it's doesn't works I used a 20M ohm resistor should I change it by a 10 ? (I speak for R1)

Changing R1 from 20M to 10M will change the frequency of the square wave when the pencil isn't touching the paper, but won't make the circuit see the graphite lines any better. Try using a soft artist's pencil (4B or more) and draw wide, dark lines.

Sorry about waste your time but I think if someone have a problem it could check on your post and see what to do...

Helping someone is never a waste of time. I'm glad to hear you found the problem and got it working.

[bigboss59400]

Changing R1 from 20M to 10M will change the frequency of the square wave when the pencil isn't touching the paper, but won't make the circuit see the graphite lines any better. Try using a soft artist's pencil (4B or more) and draw wide, dark lines.

Don't understand can you epxlain ? Is drawdio "makes" a frequency when the pencil isn't touching the paper ? but drawdio produces no sound(or if it was the case we can't hear it maybe a high or low frequancy)when the pencil isn't touching the paper so why we can set a different resistor ?

Thanks

[adafruit_support_mike]

I read the schematic wrong because I wasn't paying attention.

When the 555's output is LOW, C1 charges through RA, the pencil line, your body, and RB. When the 555's output goes HIGH, C1 discharges through RA, your body, the pencil line, and pin 7 (DISCHARGE).

R1 is a safety resistor that protects the 555. If it wasn't there, and your body wasn't making a connection between RA and RB, C1 would only have connections to pin 2 and pin 6 on the 555 chip. The TLC551 (or other low power 555 substitutes) is a CMOS chip, so the input resistance at pins 2 and 6 will be very high.. 100 megohms or more. Any charge in C1 would stay there, possibly for weeks at a time, and probably building up from static electricity as the weather changes or you move the board around.

If we allowed the charge in C1 to get too high, it could damage the MOSFETs connected to pins 2 and 6 inside the chip. R1 keeps that from happening by giving C1 a way to discharge.

R1 has very little effect on the circuit's frequency (I was wrong about that), but making R1 smaller won't help the circuit 'see' your pencil lines better. For that, you need a darker pencil.

You can check your pencil lines with an ohmmeter to see if they have enough graphite in them to work. When you touch your meter's probes to the line, about 1" apart, the resistance should be between 10,000 and 100,000 ohms. If the resistance is higher than that, you need a darker pencil line.

[bigboss59400]

OK thanks a lot for your reply no problem for your mistake...

I will check the resistance of my pencil tomorrow

Thanks for all

[bigboss59400]

Hello,

So I check the pencil line resistance (at about 1") and I get.... nothing my multimeter can't see anything (my last caliber was 200Mohm), my pencil is a 2H so I must buy another pencil with a high H ?

Thanks for all

[adafruit_support_mike]

my pencil is a 2H so I must buy another pencil with a high H ?

There's the trouble.. higher H numbers have more resistance. You want a 2B or darker: 3B, 4B, etc.

[jszsj]

Sorry for my English

...Pins 1 & 4 should be VCC, pin 8 should be GND and ...

Why pin 1 should be VCC and pin 8 should be GND? The 555's datasheet said that pin 1 goes to GND and pin 8 goes to VCC

Pin 7 should show a square wave between VCC and GND, and pin3 should show a square wave between VCC and VCC - .65v

I tested my circuit,and I don't see square wave,my pin 7 is VCC and pin 3 is VCC too, my scope is arduino with arduinoscope, I'm not sure if the frequency is too high to measure

[adafruit_support_mike]

Sorry for my English

...Pins 1 & 4 should be VCC, pin 8 should be GND and ...

Why pin 1 should be VCC and pin 8 should be GND? The 555's datasheet said that pin 1 goes to GND and pin 8 goes to VCC

Pin 7 should show a square wave between VCC and GND, and pin3 should show a square wave between VCC and VCC - .65v

I tested my circuit,and I don't see square wave,my pin 7 is VCC and pin 3 is VCC too, my scope is arduino with arduinoscope, I'm not sure if the frequency is too high to measure

If you don't hear anything from the speaker and only see VCC on the scope (even a slow one), the 555 probably isn't oscillating.

Now, you have a different username than the original poster (bigboss59400), so let me start by asking this: how did you build your circuit? Do you have an Adafruit Drawdio kit, or are you building your own version? I know all the connections on the kit's PCB are correct, but it's easy to make mistakes when you build your own version in a breadboard.

When one of my 555 circuits doesn't work, the first thing I do is look at pin 4 (RESET). If that isn't connected to VCC, the 555 won't do anything.