Drawdio problem, need help quick!

[kyo]

So I, like others it seems, am having a problem getting the drawdio working properly.

I picked up 6 kits to assemble for a 5th grade science class (they're doing stuff on sound and electricity, these are perfect for a demonstration/lesson). The schedule is currently to do this on thursday or friday.

Anyway, the problem.

I assembled 1 circuit. It is loud and clear when I touch the tabs.. but I can't get it to conduct through the pencil.

I haven't fully assembled it yet, but it should work at this point..

I attached the tape to the tab, checked that by touching it and the other tab.. works.

I attached the other end of that tape to the pencil via the pin into the lead (I shaved down the end of the pencil to verify I'm hitting directly into the graphite), but I can't get it to conduct through the pencil. I touch the other end of the pencil, nothing happens.

I have tried holding the sharp end of the pencil and touching the metal pin directly to the tab on the circuit, nothing. I have tried wrapping the copper tape around the head of the pin more to ensure a connection, nothing.

The pencil is the one that comes with the kit, with a 2b lead.

Any ideas? Obviously there is a weak link in my connection to the pencil somewhere.. but how best to find/fix it? Should I use a different setup/connection? I'm not opposed to using a different pencil or going out and buying whatever I need to make it work, but I'm on a bit of a time crunch. (I was going to buy fully assembled kits but they aren't in stock currently).

Any help would be greatly appreciated, I can provide pictures of any part if you think it'd help.

Kyle

[BruceF]

Do you have an ohmmeter? I'm not sure exactly how to interpret the tests you're describing, but is it possible that the pencil has a break in it somewhere? From a quick google search I'd guess the resistance of your 2B pencil should be well under 100 ohms if the graphite rod is intact.

[kyo]

Do you have an ohmmeter? I'm not sure exactly how to interpret the tests you're describing, but is it possible that the pencil has a break in it somewhere? From a quick google search I'd guess the resistance of your 2B pencil should be well under 100 ohms if the graphite rod is intact.

I had the same thought so I tried a few different pencils.. some worked very briefly (a blip or two) but nothing much. I don't have an ohmmeter, but I will see if I can get ahold of one in the morning.

The only thing I can figure is that my connection to the pencil is bad somehow, but I can't for the life of me figure out what is wrong.. the copper tape works, but once it is connected to the pin that's pressed into the graphite, it doesn't work.

After some more fiddling, and replacing the now very worn out copper tape..

tabs - fingers = works
tabs - finger on one end, copper tape on other = works
tabs - finger on one end, copper tape on other - pin = works
tabs - finger on one end, copper tape - pin - pencil = doesn't work when I touch the lead on the sharp end.

The pencil has to be the problem here, but I'm not quite sure what to do about it. I've tried a few different pencils now with no luck.. they can't all be broken can they?

Any suggestions on what else I could use?

Kyle

[kyo]

New result..

So now, when I have it hooked up through the graphite..

If I hold one tab, and run the other through the tape to the pin and into the graphite.. if I touch the pin or the copper tape it works. However, if I then touch the end of the pencil it cuts out.. why? I'm still holding the pin/copper, why does touching the graphite then short it out?

[adafruit_support_bill]

If I hold one tab, and run the other through the tape to the pin and into the graphite.. if I touch the pin or the copper tape it works. However, if I then touch the end of the pencil it cuts out.. why? I'm still holding the pin/copper, why does touching the graphite then short it out?

Not sure why that would be happening. Can you post a photo of both sides of the board?

[kyo]

Here are images of the board.. I can't really get a good shot of the top since the battery is in the way.





I actually did manage to get it mostly working last night through one pencil.. but it still isn't perfect, certainly not as good as the videos I've seen. I can only get a couple inches away before it fades out, even using a coin/piece of metal as a conductor on my finger.

I'm thinking that part of the issue with the pencils, is that perhaps they are cracking when the pin is pushed into them.. that's the only reason I can think of that so many don't work.

Also, anybody have any idea where I might find copper tape? After all the switching and changing things a lot of what came with the kits is worn out.

[adafruit_support_bill]

Some have reported good results using mechanical pencils (the kind with the metal tips). It is also possible to use the circuit with a paintbrush. http://vimeo.com/4434580

Copper tape can be found at electronics shops (Maybe Radio Shack if you are lucky). Or at hobby/craft stores that sell stained-glass making supplies.

[kyo]

I built the setup with paintbrushes, works perfectly.

I have tried the mechanical pencil, nothing. I can get it to conduct right up through the tip.. but the lead won't conduct the signal. I'm thinking that perhaps the lead isn't using much graphite in it? despite being 4b lead? anybody had this problem?

[crazeye]

Mine wasn't as "sensitive" as I would have liked it to be. In my opinion, RB is way too high at 300 kohm. I replaced it with a 50 kohm and it was close to what I would expect. I might even lower the resistance to about 20 kohm to see if I can make it really perform well.

Have you thought about putting in a 100 kohm pot in series with a 10 kohm resistor? I think that would be ideal so that people could tune it in to suit their soldering job and their paper type.

Cheers,
Eric