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Salvage and Reuse Motors, Gears, Switches, and More from Your Old Electronics
By Ed Sobey
Chicago Review Press Incorporated Copyright © 2011 Ed Sobey
All rights reserved.
This portable entertainment system was amazing in its day. Sony launched a revolution in 1979 when it introduced the Walkman. The model taken apart here is a later model from a rival company. Today, most cell phones have more audio features than a Walkman, and can play more songs. But one of the wonderful things about this older technology is that it houses so many useable mechanical parts.
Unscrewed Value Index 10 Cool project rating 5
Treasures to collect 5
Disposal issues 0
Drive belts and pulleys Gears LCD
Magnetic tape head Piezo speaker Rollers/wheels Springs
Flathead screwdriver Phillips screwdriver Scissors
Four Phillips screws hold the back panel to the rest of the player. Underneath the panel is the back of a circuit board; a few screws hold this board to the front frame. On the right are a motor, two pulleys, and a belt.
I lifted the circuit board off and cut the several wires connecting it to the rest of the player. In cutting wires it's always good to leave as much wire as possible attached to any components you might want to use later.
The pulley on the motor shaft belt drives a double pulley above it. This double pulley drives a second belt that powers the two white pulleys. Pressing either the "Fast Forward" or "Reverse" buttons on the top of the player moves one of these white pulleys and its associated white gears. When one of these pulleys moves, it takes up the slack in the large belt, which is how it spins without turning the other white pulley.
Between the two large white pulleys is the switch for the "Reverse" button. Pressing this button pushes together the contacts to power the circuit as well as move the pulley into place.
A few screws hold plastic retaining frames over the pulleys and the motor. These come out, freeing the belts, motor, pulleys, and gears. I used a flathead screwdriver to pry them out.
The other side of this assembly is where the tape moves. The magnetic head is here. Depressing the "Play" button moves the head onto the tape so it can read the magnetic fields of the recordings. Guide rollers guide the magnetic tape, and springs apply tension to the tape. The capstans hold the cassette in place and allow the tape to wind and unwind.
The top cover pivots open on plastic hinges so you can drop in a cassette. The plastic housing for the cassette is held to the top cover by a few screws. There is a circuit board in the top that holds the control switches and an LCD screen. Three of the switches, on the left side, are variable resistors. The others are rubber dome contact switches. Wires running from the board go to a piezo speaker that is lightly glued to the inside of the top cover. This can't produce high-quality sounds, so this player is designed to be used with earphones.
The plastic case itself could be an interesting container for small parts. You would want to cut out much of the plastic inside to leave as large a space as possible and reassemble the body. You could access the parts stored inside through the hinged top where the cassette would go.
The rollers could become wheels for a tiny vehicle. The motor, which runs on 2 volts, could drive such a vehicle with the belts.
Try messing around with the LCD. Connect various pairs of its leads to a 9-volt battery to see if you can get it to make numbers or letters. It would be interesting to test the heads to see if they put out enough voltage to generate sounds. You would have to pass the signal through an amplifier (Radio Shack sells tiny amplifier/speakers that might work nicely for this). Then run the magnetic strip on your credit card past the head so you can hear your account number.
The piezo speaker could become a pick-up head for a musical instrument, like a homemade electric guitar. Run the leads into an amplifier and try taping the speaker against the bridge of a guitar.CHAPTER 2
BAR CODE SCANNER
You've used these devices hundreds of times at the checkout stand at the grocery or to identify you as a proper card-holding patron. Now's your chance to open one up and, in the process of scientific discovery, render it impotent.
Unscrewed Value Index 4
Cool project rating 2
Treasures to collect 2
Disposal issues 0
Charge-coupled device (CCD)
Tiny lens and mirror
Rotary cutting tool
The scanner's plastic bottom comes off with the removal of four screws. This reveals a large metal weight on one side that helps hold the scanner in place on a countertop.
All the action is on the other side of the scan slot. A narrow window in the slot wall allows the light reflected off the bar code to be read inside the case, while keeping ambient light out. Two circuit boards hold the electronics. A circular array of LEDs illuminates the card: they shine through the window and reflect off the white surfaces in the code. The reflected light comes back through the window and through the center of the circular array. It reflects off an angled mirror, through a lens, and onto a detector encased in a brass housing at the far end. The brass housing has a narrow slot to admit only the light from one white bar at a time.
To get to the sensor inside the brass housing, I used a Dremel rotary cutting tool. Inside is a tiny sensor encased in a plastic envelope. The sensor appears to be a chargecoupled device, the same technology used in digital cameras. Other bar code scanners use photo-diodes to read the bars.
This scanner has a small magnetic transducer to signal the user with a sound that a card has been read or not. Inside the transducer is a coil of fine copper wire wrapped around a metallic core. This sits inside a circular or toroid magnet. A metal disk is held in place by the magnet. As electronic pulses pass through the windings, they create a magnetic field that flexes the sound-making metal disk up and down. This movement generates sound waves that tell you, for instance, "Oops, your card didn't get read."
If you haven't destroyed it, the magnetic transducer might be fun to experiment with. What sounds can you generate with it? If you wire it into a working electronic keyboard or guitar, does it make sounds like the dynamic speaker?CHAPTER 3
When you pull the trigger on a bubble gun, it lifts the applicator to cover the end of the nozzle with bubble juice, and when the fan starts, bubbles are blown out. Pulling the trigger also energizes the electric motor that both blows air through the nozzle and pumps bubble juice from the reservoir. It's a good toy, but a better take-apart. The engineering inside is inspiring. One motor performs two functions that require different rotational speeds, so gears are employed. Before you take the gun apart, insert a set of new batteries and a fresh bottle of bubble solution to give it a try; then ask yourself how you would make a device that could blow bubbles.
Unscrewed Value Index 8
Cool project rating 5
Treasures to collect 3
Disposal issues 0
DC motor Gears Pump Spring Switch
Phillips screwdriver Towel
Four visible screws hold the two halves of the bubble gun together. Two more lurk beneath the two AA batteries inside the battery case. (After removing any screws inside the battery case, you should reinsert the batteries so you can activate the gun while it's disassembled.)
Lay the bubble gun on a durable surface with the battery-case side down. (Bubble juice is bound to leak out, so you'll want to grab a towel too.) Lift off the top half. You can see that the motor drives both a centrifugal fan above and the gears below. Exhaust from the fan is forced down the plastic ducting toward the nozzle.
At the end of the nozzle is an applicator that moves up and down to spread bubble juice in front of the stream of air. This mimics how you would blow bubbles with your mouth. You dip the wand in solution and then blow air through the film of solution stretched across the circular opening. The applicator draws a sheet of solution in front of the nozzle, and then the fan pumps air out.
Excess juice drains down a drip rod into a funnel, past a check valve (you can see the shiny metal ball in the tube), back into the bottle of bubble solution.
Pushing on the trigger compresses a return spring and closes a simple switch. The switch is a piece of metal (a conductor) that the trigger forces onto the metal case of the motor, thus completing the circuit and energizing the motor. The motor turns the fan blades at high speed, spinning air in a circle and forcing it outward into the duct inside the barrel. (This is a centrifugal pump since it forces air outward.) The trigger also lifts the applicator at the end of the nozzle.
The shaft coming out of the bottom of the motor has a worm gear. This allows the motion to change direction 90 degrees and engage a set of gears that slows the motion and increases its torque. The end of this gearing is a peristaltic pump — it works like your throat swallowing a bite of Cheerios — that moves fluid by squeezing. The pump, operating at a greatly reduced speed due to gearing, squeezes a plastic tube that draws bubble solution.
Unscrew two screws holding the gears to the gun body so you can remove the gears. Lift the bottom gear and on the reverse side you'll see two plastic nubs. These press against the clear plastic tubing. As the nubs turn, they pump bubble juice along the tube from the reservoir to the barrel.
Reassembling the pump would allow you to make a tiny fountain or waterfall, though it would be more of a watertrickle than a waterfall. Or it could refill your beverage glass with the touch of a button — and you'd be the envy of all your friends.
The pump could also irrigate your indoor plants. Drive it with a microprocessor like a Stamp chip that has a soil moisture (conductivity) probe. While you're away on a trip, your pump could be activated when the soil becomes dry or when you signal it via the Internet.CHAPTER 4
Talk about a revolution in technology — from millions and millions of rolls of film used each year to nearly none.
Unscrewed Value Index 8
Cool project rating 5
Treasures to collect 4
Disposal issues -1
Charge-coupled device (CCD)
Cameras can be difficult to open, but this one required only a small Phillips screwdriver to separate the front and back halves. I cut the conductors on plastic strips running between the two halves.
The back half houses several control buttons, each held in place by small screws. The four-way mode switch allows users to pick four different menus by pushing the round switch cover in any of four directions. Beneath the cover there are three layers of plastic material. One holds four conductive tabs that, when pushed, connect two sides of the circuit below. A panel with four buttons from the lower left corner of the back half uses the same approach for entering commands. The "W" (for wide) and "T" (for telephoto) buttons, along with their electrical connections, pull out. The scene selector knob on the top of the camera pops out. Inside is a pair of metal contacts that you rotate to make connection between pairs of contacts below.
Looking at the back of the front half of the camera, the display window is the dominant component. This lifts out and can be taken apart. Inside are all the components you find in a computer LCD screen, but in much smaller sizes. Two tiny LEDs provide the light source, and several layers of plastic material provide the polarization required. If you're interested in seeing how an LCD works, taking apart a laptop screen (see page 115) would be better, as the larger size makes it easier to see things.
Beneath the display window are several interesting components. The large battery lookalike cylinder is a capacitor. The capacitor is there to power the strobe light that sits above it. If this capacitor is charged, it packs a wallop — one that you don't want zapping your fingers. To make sure it isn't charged, while holding the wooden, plastic, or rubber handle of the screwdriver (not the metal!), put the blade of a screwdriver on both contact legs of the capacitor at the same time. If it's charged, you'll see a spark. Touch it several times to make sure the charge is dissipated. Disposable cameras have similar capacitors, and even these pack a punch. The strobe requires a sudden burst of electric power at a high voltage, and the capacitors store that power and provide it quickly to the strobe.
Off to the side is the slot that the memory card slides into. This camera didn't have a memory card in it, but the connecting pins are visible.
The chip that transforms light into electric charges is now visible in the center of the camera, directly behind the lens. Like most digital cameras, this one uses a CCD, or charge-coupled device. This is an array of tiny diodes that capture light and capacitors that accumulate charge according to how much light hits their location. The charge is measured and stored as a digital value that can be converted into an image. Each diode in the array is about 3 to 8 microns in size, or about the size of a red blood cell.
The lenses offer an entirely new opportunity for components. Unlike the lenses of film cameras, these have motors in them. One motor opens the diaphragm in front of the lens to allow you to take pictures, another focuses the lens, and a third provides wide angle and telephoto zoom capabilities. The lens moves in or out to change its focal length.
Inexpensive cameras have fixed focal length lenses: you point and shoot. Some cameras offer "digital zoom": rather than moving the lens out to get images farther away, the camera uses only the image in the very center of the CCD. It blows this image up to full size — a digital sleight of hand that often disappoints.
The eyepiece has a tiny motor as well. The motor turns a shaft that rotates a plastic cam. It moves both lenses, pushing them together or apart. This action is opposed by tiny springs. It's really cool, and you have to wonder how much design thinking went into this one tiny piece. The autofocus is probably provided by an infrared LED mounted on the front of the camera.
Be sure to dispose of the battery properly.
The three tiny motors could be powered by solar cells. They could drive very small, solar-powered kinetic sculptures. The autofocus motor and gearing are intriguing. To be useful, this component might have to stay in the camera body, but the wires could come out and be connected to a switch and power.
Excerpted from Unscrewed by Ed Sobey. Copyright © 2011 Ed Sobey. Excerpted by permission of Chicago Review Press Incorporated.
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