Drawdio: A pencil that lets you draw with music! - The Drawdio kit was designed in collaboration with Jay Silver based on his original design.
When I first saw the Drawdio at Maker Faire I knew it would be a great project for beginners: A lot of fun with instant gratification! Essentially, its a very simple musical synthesizer that uses the conductive properties of pencil graphite to create different sounds. The result is a fun toy that lets you draw musical instruments on any piece of paper.
The best way to see how Drawdio works is to watch a video...
Here are some videos from JJ Silver himself! These videos are of an earlier revision so it looks a little different
Here is one of me playing with my kit right after building it
Credits
The Drawdio kit was designed in collaboration with Jay Silver & based on his original design!
When I first saw the Drawdio at Maker Faire I knew it would be a great project for beginners: A lot of fun with instant gratification! Essentially, its a very simple musical synthesizer that uses the conductive properties of pencil graphite to create different sounds. The result is a fun toy that lets you draw musical instruments on any piece of paper.
- Runs on a single AAA battery for many hours (even 'nearly dead' batteries will work)
- Use any pencil - mechanical or plain. The kit comes with a 2B pencil, the softer the lead the better
- Ridiculously fun for all ages
The best way to see how Drawdio works is to watch a video...
Here are some videos from JJ Silver himself! These videos are of an earlier revision so it looks a little different
Here is one of me playing with my kit right after building it
Credits
The Drawdio kit was designed in collaboration with Jay Silver & based on his original design!
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Signing UpStep 1: Design
How does it work?
The Drawdio kit is pretty simple compared to most electronic projects.
We will go through it one section at a time, please refer to the schematic
Power supply
The first part to understand is the power supply, which keeps everything running. The power source is a single AAA battery which is held in a plastic container that is soldered to the PCB. There is also a switch S1 which can connect or disconnect the battery from the rest of the circuit. Finally there is a large electrolytic capacitor C4, which is used as a 'bypass capacitor'. This means that it goes across the AAA battery and smooths out any ripples that are caused from power surges (like when the drawdio makes noise!)
The Oscillator
The heart of the kit is a TLC551 chip, which is a low voltage version of the famous LM555 timer chip. This integrated circuit is specifically designed for creating timers and oscillators. The original LM555 needs at least 5V to run (which is more than 3 1.5 batteries!) so we are using the 551 which can run as low as 1V. Its a little more expensive but makes the whole thing fit on a pencil.
One of the more popular ways that '555s are used is as a 'astable multivibrator' which is another way of saying an oscillator. The frequency of the oscillation is set by 2 resistors and a capacitor. The chip slowly feeds current into the capacitor until it is full and then, likewise, slowly drains it out. The resistors set how fast to fill and drain the capacitor and the size of the capacitor indicates how long it takes before it fills.
This system is pretty much identical to Japanese water fountains, as this video shows:
Except its all with electrons instead of water molecules and capacitor C1 is the 'bucket'. The water fountain oscillates maybe once a minute (1/60 Hz). But electrons are so much faster, a '555 can oscillate at thousands of Hertz, which means it can make audible sound. (Human hearing tends to range from 20Hz to 20000 Hz)
f = 1.44 /(C3 * (RA + 2 * RB))
C3 = 680 pF = 0.00000000068 F
RA = 10000 ohms
RB = 300000 ohm to 1000000 ohm (1 Mohm)
In this case, we use two resistors RA and RB but also have an 'open connection': two tabs at the end of the PCB. If the two tabs are shorted with a piece of wire, then the frequency of the oscillation is 3500 Hz, if instead there is a resistor of 1 Megaohms between the two tabs, the frequency of oscillation is about 1000 Hz. You can use a calculator to do the math yourself using the formula above
Instead of a 'everyday' resistor between the tabs, however, we use something else - the conductivity of the human body and graphite! The human body has a resistance similar to a 200,000 ohm resistor. Graphite has resistance of about 1 ohm per inch when its in the form of a pencil lead. When its spread out on a piece of paper, the resistance goes up a lot, up to a megaohm for a few inches of 'drawn resistor'
Amplifier
The 551 can create audio-frequency oscillations but it is not powerful enough to play them on a speaker, just like an MP3 player needs an amp to play music on large speakers. That's because the 551 was designed mostly for digital logic, not for low impedance (8 ohm) audio outputs. So we will use a Class B 'pushpull' amplifier, which uses two separate transistors to amplify the sound.
This is pretty much the same thing in your stereo, except your stereo has enormous transistors with gigantic heatsinks so that it can drive large speakers.
The Drawdio kit is pretty simple compared to most electronic projects.
We will go through it one section at a time, please refer to the schematic
Power supply
The first part to understand is the power supply, which keeps everything running. The power source is a single AAA battery which is held in a plastic container that is soldered to the PCB. There is also a switch S1 which can connect or disconnect the battery from the rest of the circuit. Finally there is a large electrolytic capacitor C4, which is used as a 'bypass capacitor'. This means that it goes across the AAA battery and smooths out any ripples that are caused from power surges (like when the drawdio makes noise!)
The Oscillator
The heart of the kit is a TLC551 chip, which is a low voltage version of the famous LM555 timer chip. This integrated circuit is specifically designed for creating timers and oscillators. The original LM555 needs at least 5V to run (which is more than 3 1.5 batteries!) so we are using the 551 which can run as low as 1V. Its a little more expensive but makes the whole thing fit on a pencil.
One of the more popular ways that '555s are used is as a 'astable multivibrator' which is another way of saying an oscillator. The frequency of the oscillation is set by 2 resistors and a capacitor. The chip slowly feeds current into the capacitor until it is full and then, likewise, slowly drains it out. The resistors set how fast to fill and drain the capacitor and the size of the capacitor indicates how long it takes before it fills.
This system is pretty much identical to Japanese water fountains, as this video shows:
Except its all with electrons instead of water molecules and capacitor C1 is the 'bucket'. The water fountain oscillates maybe once a minute (1/60 Hz). But electrons are so much faster, a '555 can oscillate at thousands of Hertz, which means it can make audible sound. (Human hearing tends to range from 20Hz to 20000 Hz)
f = 1.44 /(C3 * (RA + 2 * RB))
C3 = 680 pF = 0.00000000068 F
RA = 10000 ohms
RB = 300000 ohm to 1000000 ohm (1 Mohm)
In this case, we use two resistors RA and RB but also have an 'open connection': two tabs at the end of the PCB. If the two tabs are shorted with a piece of wire, then the frequency of the oscillation is 3500 Hz, if instead there is a resistor of 1 Megaohms between the two tabs, the frequency of oscillation is about 1000 Hz. You can use a calculator to do the math yourself using the formula above
Instead of a 'everyday' resistor between the tabs, however, we use something else - the conductivity of the human body and graphite! The human body has a resistance similar to a 200,000 ohm resistor. Graphite has resistance of about 1 ohm per inch when its in the form of a pencil lead. When its spread out on a piece of paper, the resistance goes up a lot, up to a megaohm for a few inches of 'drawn resistor'
Amplifier
The 551 can create audio-frequency oscillations but it is not powerful enough to play them on a speaker, just like an MP3 player needs an amp to play music on large speakers. That's because the 551 was designed mostly for digital logic, not for low impedance (8 ohm) audio outputs. So we will use a Class B 'pushpull' amplifier, which uses two separate transistors to amplify the sound.
This is pretty much the same thing in your stereo, except your stereo has enormous transistors with gigantic heatsinks so that it can drive large speakers.
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(the voltage on those electrolytic caps is the maximum you can use them with)
I have some notes on this on the Drawdio website here
http://web.media.mit.edu/~silver/drawdio/make.htm
The basic trick is to attach one side of the circuit to a *metal tipped* mechanical pencil. I like 0.7mm but try a couple out and see what you think. You can test them before even mounting: just draw a line and touch (or clip) one side of the drawdio to the line... then hold the other side with your hand and touch the other end of the line with your hand.
Is the main IC a bog-standard 555 timer?
Noticed the same thing on ladyada's site.
I'm using TS555C with a coin cell battery and I'm only getting low hz almost none changing static :(
Not sure what that could be...
but if i bought the kit how would i add a line out type deal so i could put it through guitar pedals and computer effects and the like.
thanks
jook
teehee
What sort of component ranges can I have (do the caps have to be spot-on or is there leeway?) I think I have most of the components already apart from the 551. Can I use a AA cell rather than a AAA? If i simply whack a bigger battery in and change it to a 555 will there be any issues?
etc. etc.