Are you breathing? Do you have a gadget that can be charged via a USB
port? Well if you answered yes to both, then you are in luck. This
instructable shows how to make a device that will charge your
USB-capable devices while you do what you do best. Breathe. Using some
parts scavenged from an old CD-ROM drive, a simple electronic circuit,
and a few rubber bands you will soon be huffing and puffing your way to
fully-charged pseudo-useful electronic gadget nirvana.
Introduction and Step 1
This project requires a wide range of "maker" skills, such as PCB board
manufacture, dismantling of electronics, cutting and drilling plastics,
mixing epoxy, designing a gear train, kludging together a bunch of
parts, bending paper clips, and risking the well being of your ever so
expensive phone, camera, or PDA. All in all, good fun.
Since
everyone will have a different collection of junk parts to build this
from, I will just give you a detailed overview of how I went about it
and you can apply these ramblings to your own project. Which will
consist loosely of four steps.
1. Scrounge up some suitable parts for the generator
2. Build the charger circuit
3. Assemble the generator, thorax coupler, and mechanical return
4. Connect the charger circuit, and test
Step 1:
I
had about four old CDROM drives hanging around and took apart a few of
them to see what cool parts were inside. Turns out there are lots of
cool motors, gears, and other parts inside that fully validate my
insistence of keeping such crap laying around. Seeing the gear trains
inside these units used for opening the tray gave me the idea for this
project. The small low-torque, high-RPM motor is linked to the tray via
a gear train that has a final ratio of about 20:1 Previously I had
been using a parallel array of tiny pager motors to generate electricity
from breathing (see below) but the linear travel from your chest
expansion is not that great (around an inch) so in order to generate
useful voltages you had to really huff and puff.
Anyway, tear
into those CDROM drives, which you can find at pretty much any garage
sale, thrift store, or landfill. The pic below shows the results. Lots
of potential projects in there. For now, we are only interested in the
plastic gears and the motors for opening the tray and/or moving the
laser carriage.
Look over the various gears and drives and try
to visualize a way to add additional gears to increase the gear ratio,
or how to add another motor in series. You want to minimize the changes
to the gear train. Alternatively you can just scavenge all the gears
and build your gearbox up from scratch.
You are also going to
need at least one motor with a small gear or pulley on it so that you
can connect it to the gear train. The motors in the CDROM drive are
typically simple permanent magnet DC motors designed to run on 5V,
except for the spindle motor, which you don't want to use anyway.
At
this point you also want to think about what you are going to use for a
strap to go around your chest. An old belt, some webbing, an old
shoelace, a name badge strap, or anything that will fit around you
comfortably without any stretch to it. You want all the expansion to
take place in your linear generator. Any stretch that occurs in your
thorax coupler will be wasted energy.
Step 2 - Build the charger circuit
The charger circuit is pretty simple. It consists of:
1. A diode bridge to turn the AC voltage from the generator into rectified DC.
2.
A rechargeable battery to level out the voltage and hold excess
generated power when nothing is hooked to the USB port. You could use a
big capacitor too, but batteries offer a more predictable voltage
level.
3. A boost converter to bring the low voltage up to 5VDC for USB charging
4. A USB plug.
I've drawn up the circuit in EAGLE, a program that I highly recommend. You can download it for free from
cadsoft.de.
The schematic and single layer board layout are attached. The actual
use of EAGLE and the board manufacture are beyond the scope of this
instructable. Many great instructables are out there to cover these
topics.
The parts list for the charger circuit (quantities in bold):
1x L6920 Adjustable output step up DC converter (1V minimum input,
Datasheet here)
Digikey# 497-4593-1-ND
4x 1N4148 switching diodes (I used tiny SOD523 smds, but you can sub in what you have handy)
Digikey# 1N4148WTDICT-ND
2x 10uF ceramic or other low ESR capacitors (I used 1206 smds)
Digikey# 39901299-1-ND
2x 100k thin film resistors
Digikey# P100kFCT-ND
1x 10uH wirewound inductor
Digikey# 490-2519-1-ND
1x USB female Type A smd connector
Digikey# AE9924-ND
Above you can see the schematic and board files, and jpegs of them as well.
The tough part is making a good PCB in your kitchen that has traces
small enough for the TSSOP package of the L6920. As you can see in the
pic, I made 4 boards at once since each is so small.
The trick
to putting it together is to start in the middle and move your way out,
begin with the L6920, and add the SMD discretes as you go. A pair of
tweezers is essential, along with good eyes or a magnifying glass,
bright light, and a steady hand. Don't worry about getting too much
solder in there, use your solder wick to clean up any accidents, and
check your work with a multimeter after every step. Practice makes
perfect.
Step 3 - Build the generator
Now you need to make the generator. You should play around with the
gears and motors until you get a satisfactory arrangement. You will
want to use a multimeter on the motor while turning the gears to see how
much voltage you are getting. You want to get in the 2-3 volt range
while moving the linear gear slowly about an inch in travel. When
setting up the gears, you want to use the ones that have a large gear
molded with a smaller gear. Stacked in series these will give you a
good gear ratio as shown in the drawing. (ignore the fact that the
teeth are the wrong size in the drawing, I was too lazy to redraw with
matching tooth pitch) You should shoot for somewhere in the 25-50:1
range. More is better but eventually the losses in the gear train pile
up and it get too hard to turn the motor and the gears will strip.
One of the keys is to find a way to use the linear gears on the CD
tray or other piece to turn your breathing motion into rotation of the
DC motor. I included a pic of another prototype version of the CD drive
generator where you can see the linear tray gear clearly. Also visible
are the cut marks in the plastic. This prototype was also capable of
lighting the LED array pictured. Don't be afraid to chop this thing up
to suit your needs.
In the other pic the DC motor is mounted in place in the plastic of
the drive I cannibalized. Near this was a linear slider that I used to
couple the breathing motion to the gear train. I also added another gear
(see pic) to the drive train in order to increase the ratio and to
allow mounting another motor in the future to increase output. The main
challenge is to effectively get the breathing effort translated into
rotation of the motor efficiently.
Step 4 - Put it all together and test it out
Once you have a satisfactory generator setup, then you want to connect
the generator to the charge circuit, insert the battery, and use your
multimeter to test the output voltage at the USB port. If you don't see
5V then there is a problem. Fix it before plugging your pricey gadget
into the USB port.
Below you can see my assembled breath powered
USB generator in all its glory, top and bottom. You can see the rubber
band used for return, along with the linear gear carriage, the strap and
the paper clip I used to connect the linear gear to the strap. The key
here is to have all motion transferred to the linear gear so you want
the strap and connection method to be stiff with no give. The strength
of the rubber band or spring return is up to you. My half-assed
experiments indicate that you can pretty much handle a 1N force without
feeling too labored in your breathing. Ideally you want as small a
rubber band as will return the linear gear to the starting position when
you exhale. If you get enough generating capacity either through high
gear ratio, extra motors, or a bigger motor, then you will need a bigger
spring return. Essentially you are storing mechanical energy during
your inhalation that is used to turn the generator on the exhalation so
that you can generate on both push and pull. You need the diode bridge
to successfully take advantage.
So I strapped on this monstrosity and hooked it up to my trusty data acquisition box from
DataQ.
Attached is the voltage plot output of the generator before step-up
conversion to the 5V USB. Basically the battery runs the step up
converter and the breath generator charges the battery. In the plot you
can see the leveling effect of the battery, with the voltage spikes
when I was breathing. Actually I was approaching hyperventilation, but
in the name of science. The results can be seen in the photo of the
phone charging. One thing to mention is that I had to modify a USB
cable to get the RAZR to charge as
detailed on this website. I don't have any solid numbers on the power I was generating, I haven't come up with a good way to measure that yet.
Typical
resting metabolism is on the order of 50-75W of which a substantial
portion is due to breathing effort (I have seen north of 50%). So if we
assume 25W continuous energy used for breathing, it seems reasonable
that we could increase that 4% to harvest 1W for charging a cell phone.
Based on my cell phone, and these assumptions it would take about 3
hours to charge the 3.7V 800mAh battery. Assuming 100% efficiency.
Sadly,
based on the few measurements I was able to make, the breathing
generator I built is putting out more like 50mW. Way to breathe no
breath. It would charge the phone, but the NiMH battery would be doing
most of the work until it was drained. Then you would have to breath
for a day or so to recharge the NiMH battery. You were planning on
doing it anyway right? So there is room for improvement. One area I am
looking into is using carbon nanotubes and polyurethane to make an
electroactive polymer generator. This is the type of technology that is being used to make
boot-strike generators for the military.
Future
improvements could get this device into the 1W range. Specifically,
using a better DC motor (higher voltage per rev) and custom building the
drivetrain to be more comfortable and better coupling to breathing
motion.
