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
The Drawdio kit was designed in collaboration with Jay Silver & based on his original design!
Step 1: Design
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
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 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'
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.
Step 2: Make It! Preparation
This is a very easy kit to make, just go through each of these steps to build the kit
1. Tools and preparation
2. Check the parts list
3. Assemble it
Learn how to solder with tons of tutorials!
Don't forget to learn how to use your multimeter too!
There are a few tools that are required for assembly. None of these tools are included. If you don't have them, now would be a good time to borrow or purchase them. They are very very handy whenever assembling/fixing/modifying electronic devices! I provide links to buy them, but of course, you should get them wherever is most convenient/inexpensive. Many of these parts are available in a place like Radio Shack or other (higher quality) DIY electronics stores.
I recommend a "basic" electronics tool set for this kit, which I describe here.
Soldering iron. One with temperature control and a stand is best. A conical or small 'screwdriver' tip is good, almost all irons come with one of these.
A low quality (ahem, $10 model from radioshack) iron may cause more problems than its worth!
Do not use a "ColdHeat" soldering iron, they are not suitable for delicate electronics work and can damage the kit (see here) http://www.epemag.wimborne.co.uk/cold-soldering2.htm
Solder. Rosin core, 60/40. Good solder is a good thing. Bad solder leads to bridging and cold solder joints which can be tough to find. Dont buy a tiny amount, you'll run out when you least expect it. A half pound spool is a minimum.
Multimeter/Oscilloscope. A meter is helpful to check voltages and continuity.
Flush/diagonal cutters. Essential for cutting leads close to the PCB.
Desoldering tool. If you are prone to incorrectly soldering parts.
'Handy Hands' with Magnifying Glass. Not absolutely necessary but will make things go much much faster.
Good light. More important than you think.
Check out my recommendations and where to buy.
Step 3: Make It! Parts List
Check to make sure your kit comes with the following parts.Sometimes we make mistakes so double check everything and email email@example.com if you need replacements!
Description: Printed circuit board
Description: TLC551 or similar low voltage '555 timer chip
Description: NPN transistor, EBC pinout Such as PN2222 or 2N3904
Description: PNP transistor, EBC pinout Such as PN2907 or 2N3806
Description: 680pF ceramic capacitor (681)
Description: 0.1uF ceramic capacitor (104)
Name: C2, C4
Description: 100uF / 10V capacitor
Description: 1/4W 5% 10K resistor Brown, Black, Orange, Gold
Description: 1/4W 5% 300K resistor Orange, Black, Yellow, Gold
Datasheet: E-Switch EG1218
Description: AAA battery holder
Datasheet: EPD BH412
Description: Small 8ohm speaker
Datasheet: Kobitone PS603
Name: Copper foil tape
Datasheet: 3M 1181
Distributor: Any stationary store
Distributor: Any stationery store
Name: Zip Tie
Distributor: Any hardware store
Distributor: Any electronics or hardware store
Step 4: Make It! Solder It! Part 1
Get ready by placing the PCB in a vise
Heat up your soldering iron to 700deg F, clean the tip and make sure your sponge is wet
First thing we will place is RA, a 10K resistor (brown, black, orange gold). This resistor sets the brightness of the indicator LED.
Bend the resistor into a staple as shown, and slip it in. (The stock photo at left shows a 100 ohm resistor but just ignore the stripes and focus on the shape)
Place the resistor in the location marked RA. Resistors do not have polarity which means you can put it in 'either way' and it will work just fine. Bend the wire legs out so that the resistor sits flat against the PCB.
Turn the PCB over. Using your soldering iron tip, press and heat both the pad (the silver ring around the hole) and lead (wire) at the same time for 2 or 3 seconds. Then poke the end of the solder in to create a nice solder joint. Do this for both leads.
Using your diagonal cutters, cut off the long leads just above the solder joint.
Next is the other resistor, RB. This resistor has a different value, 300K. The stripes are Orange Black Yellow Gold.
Solder in this resistor using the same technique you used for the first resistor.
Clip the resistor
Step 5: Make It! Solder It! Part 2
C3 is a 0.1uF capacitor and has a "104" marking on it. C1 is the 680pF capacitor and has a "682" marking on it.
Place the capacitors so that the 2 legs (leads) slide thru the two metal holes in the PCB (pads). The capacitor will sit flat against the PCB.
Solder in the capacitors
Clip the leads
Next is the power switch. The switch is symmetric so it will go in 'either way'
You may want to use a piece of tape to keep the switch against the board while it is being soldered.
Once it is soldered in, clip the leads
Next is the heart of the kit, a low voltage 555 timer chip. This one is called the TLC551. The important thing to note about the chip is that it is not symmetric. If it is put in wrong it will not work! Its also nearly impossible to fix if the chip goes in wrong so make triple-sure before you solder it in!
The silkscreen on the PCB has a little notch in the top. That notch indicates where the top of the chip is. If you look on the chip, there is a circle/dot imprinted in it on one end. There's also a TI logo at that side. Make sure the chip is inserted so that the top of the chip lines up with the silkscreen notch. Check the photo to the left if you're not sure.
Solder in all 8 pins. You might want to use a piece of tape to hold the chip in place, or use a spare finger if you are dexterous.
The leads are very short to they wont need clipping.
Step 6: Make It! Solder It! Part 3
Electrolytic capacitors are polarized and must be placed correctly or the circuit will not work. The longer lead is the positive (+) one and must go into the pad marked with a + as shown
Fold the capacitors down so that they lie flat against the PCB.
Solder them in, and clip the leads
Next are the two transistors Q1and Q2. They are matched, one is NPN (Q1) and one is PNP (Q2). The importing thing to notice is that although they look very similar, they are different.The NPN has a "2222" marking on it. The PNP has a "2907" marking.
Make sure that the PN2222 goes into the NPN slot, and the PN2907 goes into the PNP slot!
Make sure the shape of the transistors matches the silkscreen shape as shown. The transistors will sit a few mm above the PCB.
Flip over the PCB and solder in the two components
Then clip the longer leads
After soldering in the transistors, you can bend them down a little so they sit almost flat-faced to the PCB.
Step 7: Make It! Solder It! Part 4
Next, nick the insulation 1/4" from the ends of the wire, and pull it off. If you have 'wire strippers', use them as they are a little easier!
Next, it is a good idea to tin the ends of the wires. Its a little tricky because it requires holding three things. However, if you have a 'third hand tool' or a vise, you can use that to hold the wire while you heat up the stripped end and coat it with a little bit of solder. This will make it easier to connect to the speaker.
On the opposite side of the speaker there are two solder tabs. Heat them up and add a little more solder. Don't spend too much time on them (more than 3-4 seconds) since the speaker is made of plastic and if it heats up too much it will melt!
Next, warm up the tabs and slide the tinned ends of wire into the melted solder pool. Then remove the iron and wait a few seconds, the solder pool will cool with the wire in place. Do the same for the other pad
Twist the wires, this will reduce the strain on the solder joints when bending. Put the end of each wire into the PCB hole marked SPK. The speaker is 'symmetric' so it doesnt matter which wire goes in which hole.
Solder the wires into place.
Step 8: Make It! Solder It! Part 5
Slide the battery holder into the PCB (but do not solder it in). Make sure that the battery is aligned correctly. Putting in the battery backwards shouldn't damage the circuit but its still not a good idea so try to get it right the first time. The back of the PCB has a silkscreen to help determine which way the battery goes in.
With the battery holder in place (but, again, not soldered in) and the switch in the ON position, touch both sides of the PCB. A squeaking noise should come out of the speaker! As you press harder/softer, the pitch will change. That indicates the circuit is working.
If its not making noise, try:
1. Wiggle the battery holder a little to make sure its making contact
2. Check that the switch is turned on
3. Check that the components are correctly placed and soldered well. Re-touchup the solder points in case you have cold solder joints.
Once you are tested and happy, its time to finish up!
Remove the battery and place the battery holder on top of the components, as shown. Bend the leads a little so that it sits as tight as possible.
Solder in the battery holder, and clip the leads short.
Step 9: Make It! Solder It! Part 6
Next cut a 1.5" piece of copper tape using the diagonal cutters. Don't use scissors as the metal tape can damage them. peel off the paper backing. The copper tape is conductive, sticky and flexible which makes it perfect for wrapping the pencil
Wrap the tape along the top of the pencil so that the beginning is at the silver metal tab on the PCB, as shown
Then take the thumbtack and gently push it into the end of the pencil. You might have to twist it back & forth a little to get it all the way in. The thumbtack will grip the copper tape and also make contact with the graphite in the middle of the pencil to make the first half of the drawing sensor
Next take 3 or 4" of copper tape and start wrapping around the bottom of the pencil, starting with the silver tab on the PCB and ending an inch before the end of the pencil. This will make contact with your hand and provide the second half of the sensor.
Solder the copper tape to the tab directly as shown
Finally, insert a battery and turn on the kit. Then grip the pencil with one hand and touch the point of the pencil to your other hand. You will be able to hear the drawdio make noise!
Next up, see the user manual for ideas on how to make the most of your drawdio
Step 10: Use It!
The Drawdio is simple to use. Simply grip the pencil in one hand so that you're making good contact with the copper tape. Then draw a circle on the paper and touch it using a finger from the other hand
This allows your body to act as the sensor. The voltage is very low (about 1 volt) which is very safe. As long as you stick to the single battery, there are no health risks.
Choosing a pencil
The 'softness' of the pencil lead will affect how thick the drawn lines are and thus the sound of the pencil. Experiment with hard and soft leads as well as sharpening or blunting the point to see how that affects the drawdio sound
Mechanical pencils also work well. However, you may have to put an insulative layer (like packing tape) on the lower section of the pencil if the body is completely metallic.
And some from happy & noisy customers!
Ideas for experimentation
- Try different kinds of paper, and pencils
- Place a copper coin (like a penny!) on the drawing and use that to make contact with the graphite - it will make the surface area larger and reduce the resistance of the drawing
- Hold hands with someone and 'draw' on their skin with the pencil
- Wash and lightly dry your hands to make them a little more wet than usual, this will also affect the pitch