Intro: Feel-The-Code Reader - Part 3: Amp Hardware
Feel-The-Code (F-T-C) is a vibra-tactile Morse Code text reader. It has a software component and a hardware component. Its purpose is to make it possible to read any text file silently and without looking at the computer. With F-T-C a person who is blind can read text easily and unobtrusively.
Part 1 of the project described the free F-T-C software (Pic 2) and how to use it. I would suggest you read that IBL before you start to building the vibra-tactile component described here.
Part 2 of the project described a vibra-tactile component (Pic 3) based on a LED controller harvested from a USB keyboard. Part 2 also has the construction details for a vibra-motor tip that can be used with either that controller or this one.
This is Part 3 of the F-T-C project and it describes a way to control the vibra-motor tip using audio tones and an audio amplifier (Pic 4).
The vibra-tactile component shown here can be built for about $30 even if you have to buy all the parts. It is compact and portable and can be used with a PC using the F-T-C software or it can be used with a mobile device like a smart phone using another Morse Code app.
Some soldering to small electronic parts is required so review one of the IBLs on soldering if you are new to this.
Step 1: Choices
Small portable speaker systems for use with computers, MP3 players and smart phones come in four basic forms. These are:
1. Unpowered speakers
2. Battery-powered amplified speakers that connect to the 1/8" headphone jack
3. USB-powered amplified speakers that connect to the 1/8" headphone jack
4. USB-powered amplified speakers that use USB for the audio as well as the power
Choices 2, 3 and 4 can all be modified to work with the F-T-C system. An unamplified speaker system won't work.
If you want to use the F-T-C system only on a PC then the best choice is probably number 3 or 4 as there are no batteries to hassle with. Number 4 choice is the neatest with just a single USB cable connecting to the PC.
If you want to use the F-T-C system with smart phones (as well as with a PC) then the choice is number 2. That is what is described in the following steps here.
The basic idea is the same in all cases. We amplify the audio from the PC or smart phone. Then we use a full-wave bridge to produce DC from the amplified audio which drives the relay coil. The reed contacts in the relay then switch the battery power on and off to the vibra-motor.
Note: Some battery-powered speakers use just two or three cells (3-4.5 VDC). These will probably NOT be able to drive the relay. Look for speakers that use at least four cells (6 VDC) and/or have a wall wart plug-in option that is 6 or more volts. The Kinyo model shown here had a 9 V wall wart we could easily replace with a 9 V battery.
Step 2: Tools and Parts
All prices are estimates.
Small side cutter
20-40 Watt soldering iron (RadioShack #64-2184)
Rosin-core solder (RadioShack #64-009 )
Small Phillips screw driver
Drill with 1/4" bit
Optional, but handy:
Hot glue gun and sticks
Prepunched Perfboard (RadioShack #276-1396) $3
Battery snap connector 9 V (RadioShack #270-324) $2
Battery 9 V holder (RadioShack #270-326) $1
Battery 9 VDC (Dollar Tree) $1
Parts for relay board:
Kinyo Audio Zone 2.0 Amplified Speaker System (Big Lots) $7
Relay 5VDC (RadioShack #275-0232) $4
Full-wave bridge (RadioShack #276-1152) $3
Tantalum capacitor 10 uFd 16 V (RadioShack #272-1436) $2
Resistor 100 ohm 1/4 watt (RadioShack #271-1311) $1
Jack 1/8" mono (RadioShack #274-0251) or stereo (RadioShack #274-0249) $3
Parts for vibra-motor tip:
Vibra-motor 3VDC (RadioShack #273-0107) $4
A pill bottle
Plug and wire (Dollar Tree myTunes 1/8" Extension Cable) $1
Step 3: Modify the Audio Amplifier
This amplified speaker system is typical of many powered portable speakers. It is designed to be used with a wall wart but can be easily adapted for battery use. It is a stereo system but we will only use one channel.
Cut cable to second speaker next to the main enclosure and discard (recycle) it.
Remove two screws from top of main enclosure and lift off front (Pic 2).
Unsolder both wires from the internal speaker (Pic 3).
Cut four hookup wires 4" long and strip and tin the ends of them all. I used a red, a black and two yellow wires for these pictures.
Make a two-wire harness with the battery snap connecter attached to the red and black wires (Pic 4).
Solder one end of red wire to outer diode (D2) and the black wire to the innermost diode (D4) as shown in Pic 5.
Connect a 9V battery and test that the LED comes on when the switch is pressed.
Step 4: Build the Relay Board
A full wave bridge with a filter capacitor is connected to the AC audio output from the right channel of the amplifier. The DC from the bridge is used to close the reed relay which switches 9 VDC from the battery on and off to the vibra-motor.
The top view of the relay board shows the position of the four parts on the board.
Cut an 8-hole X 11-hole perf board piece and mark the 12 holes as shown in Pic 2. This will be the bottom side of the board.
Mount relay in the four holes shown outlined in blue in Pic 3
Mount the full-wave bridge in the four holes outlined in red. Be sure the "+" lead is in the position shown.
Mount filter capacitor in the two holes outlined in green with the "+" lead in the position shown.
Mount the resistor in the remaining two holes outlined in brown.
Position the leads as shown in Pic 4.
Step 5: Install the Relay Board
Unscrew the screw holding the main printed circuit board (PCB) and lift it free.
Unsolder the speaker wires from the left channel and the right channel PCB pads. Solder the two yellow wires to the two left channel contact pads.
Put the main PCB back in position and reinstall the screw to hold it in place.
Solder the red, black and two yellow wires to the relay board in the positions shown in Pic 2. Push the tinned end of each wire from the top side of the relay board through the appropriate hole and solder it in place on the bottom side.
Solder two wires to the 1/8" jack solder lugs (use lugs 1 and 3 if you are using a stereo jack). I used a green and a brown wire in the picture. Connect the other ends of these two wires to the relay board in the positions shown.
Drill a 1/4" hole for jack in the back cover and screw the jack in place.
Test the amplifier and relay board and then screw the top back on the enclosure.
Step 6: Build the Vibra-Motor Tip
Building one kind of vibra-motor tip was described in Part 2 Step 6.
You can use that kind of a tip if you prefer it over the one described here. Either tip can be used with either the LED-based controller or this Amplifier-based controller. The tips are all basically the same.
Here are pictures of a tip built in a pill bottle. The cable with the 1/8" plug goes through a hole in the cap of the pill bottle (Pic 1). The vibra-motor is connected to the cable wires (Pic 2), wrapped in sound-absorbing foam and glued in the pill bottle. The top is then screwed on the bottle (Pic 3). Be sure the eccentric weight on the vibra-motor is clear of any obstruction and can rotate freely.
Test the vibra-motor tip by plugging it into the relay box and sending audio tones from the PC or smart phone. The vibra-motor tip should vibrate actively when a tone is present. Adjust the amplifier volume up until the vibra-motor action is reliable.
Step 7: Variations in Design
There are lots of possible variations you can make to suit the needs of a person with specific sight, hearing or physical limitations.
Put in smaller case or box.
Consider putting the vibra-motor in a wrist band so it can be worn and used hands-free.
Consider a small vibra-motor tip that attaches to the headpiece, armrest or seat of a wheelchair.
Perhaps the vibra-motor could be included in a sip-and-puff mouth controller used by a paraplegic.
The variations are almost endless so get to work and Feel-The-Code!