Intro: Feel-The-Code Reader - Part 2: LED 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 the vibra-tactile display.
The hardware vibra-tactile component (Pic 3) described here is based on a LED controller harvested from a USB keyboard. It can be built for as little as $25 even if you have to buy all the parts. It is compact and portable so it can be carried from PC to PC.
Some soldering to small electronic parts is required so review one of the IBLs on soldering if you are new to this. https://www.instructables.com/id/How-to-solder/
Step 1: Tools and Parts
Small side cutter
20-40 Watt soldering iron (RadioShack #64-2184)
Rosin-core solder (RadioShack #64-009 )
Small screw drivers
Drill with 1/8" and 1/4" bits
Hacksaw or other fine-toothed saw
Optional, but handy:
Hot glue gun and sticks
Hookup wire 24 or 30 guage stranded
Fix-all adhesive (Dollar Tree) $1
Foam sheet from hobby store saved from packing material
Parts for relay box:
USB (wired, NOT wireless) Keyboard (Walmart ONN brand) $10
Project Enclosure 4"X2"X1" (RadioShack #270-1802) $4
Relay 5VDC (RadioShack #275-0232) $4
Jack mono or stereo 1/8" (RadioShack #274-0249) $3
Parts for haptic tip:
Vibra-tactile motor 3VDC (RadioShack #273-0107) $4
(or from cheap battery-powered toothbrush - Pic 3)
CVPC 1/2" pipe and end caps or any small container like a pill bottle
Plug and wire (Dollar Tree myTunes 1/8" Extension Cable) $1
Step 2: Wire the Relay
The reed relay is hooked in parallel with the selected LED and switches 5VDC from the USB connection to the vibra-tactile motor.
Prepare four 24 guage hookup wires (Pic 2). Different colored wires help to make the description clearer. If you use all the same color, be sure to keep clear which is which when you hook them up later. The wire lengths are not critical, but the suggested lengths are sufficient.
Each wire needs to have 1/8" of insulation stripped from both ends. The 3" red wire needs to have one end stripped an additional length so it has 1/4" tinned at one end and 1/8" tinned at the other end. The stripped area is then "tinned" as described in the soldering IBL listed above.
The wires are:
3" long red wire.
3" long yellow wire.
6" long black wire.
2" long orange wire.
The relay has four connections which I have labelled in the diagram (Pic 1). Connections 1 and 2 are the coil and connections 3 and 4 are the reed switch.
Solder one end of the 3" yellow wire to connection 1.
Solder the 1/4" end of the 3" red wire to both connection 2 and connection 3.
Solder the 2" orange wire to connection 4 (Pic 3).
Lay the 6" black wire along the side of the blue relay case (no electrical connection to the relay) and tape it in place so that about 3" sticks out along side the red and yellow wires.
Wrap two 3" lengths of electrical tape around the relay to hold the black wire in place and insulate the relay connections (Pic 4).
Step 3: Harvest Keyboard PCB
Now remove all of the screws from the bottom of the USB keyboard (keep them for later) using a small Phillips-head screwdriver. Often one or two screws will be hidden beneath a label or sticker so be sure to remove them all. This should allow you to separate the top from the bottom of the keyboard. (Don't worry if there are dozens of small round flexible contacts as we will just discard them anyway.) Find the printed circuit board (PCB) with the three LEDs on it and remove the screws holding it in place. Separate the PCB (Pic 2) from the plastic key contact sheets and discard all but the PCB.
(Note that some of the bigger, fancier keyboards have two or three PCBs connected by ribbon cables. We need all of them.)
Test the separated PCB by plugging the USB cable into your PC and toggling the caps lock, num lock and screen lock on and off. The LEDs on the PCB should turn on and off. Note which LED is the screen (sometime marked "SCR" on the PCB) lock as we will use it later (Pic 3).
Step 4: Connect the Relay
If you are using a jack solder the black wire to the shell connection and the white wire to the tip connection.
Connect the three wires (red, yellow and black) from the relay to the PCB as follows.
The red wire is soldered to the the point where the red wire of the USB cable connects to the PCB.
The black wire is soldered to the point where the black wire of the USB cable connects to the PCB. (Note that it may be a lot easier and safer if you follow the PCB trace away from the USB cable connection to a solder point without any near neighbors. The black ground trace is usually quite wide and travels the length of the PCB.)
The yellow wire connects to the signal side of the SCR LED we identified above. The signal side of the SCR LED is usually marked with a "-" sign and it usually has a thin trace that leads to the IC chip. (The side of the SCR LED we DON'T want is the "+" side which usually connects to the other two LEDS and not to the IC.) This is a very small connection on the PCB so be sure to use a minimum of solder and check that there are no shorts to nearby leads!
The black and orange wires get soldered to pin 1 and 3 of the jack (Pic 2). If you are hardwiring the vibra-tactile tip to the relay box (with no plug and jack) we will connect to these two wires later.
Step 5: Install in Box
Now check that the box ("enclosure") you have is big enough for the PCB to fit inside. Drill a 1/8" hole centered on each end of the box. Use the saw to make a slot from the 1/8" hole up to the rim of the box on one end (Pic 2). Enlarge the 1/8" hole at the other end to 1/4" if you are going to use a jack for the haptic tip connection (recommended). Mount the PCB in the box using a couple of screws (from the keyboard) or some glue (Pic 3). Be sure the USB cable slips down into the slot and fits into the 1/8" hole there. The jack is secured in the 1/4" hole in the other end of the box (Pic 4).
Test the relay box on your PC again to be sure the LED still can be turned on and off and then screw the top on enclosure.
Step 6: Build the Vibra-Tactile Tip
There are a lot of ways to make a small case for the vibra-tactile motor. I use 2" pieces of CVPC (plumbing) 1/2" tubing a lot. There are matching end caps that make it easy to hold. The goal for whatever you make is that you can enclose it in your hand to suppress any sound but the vibrations are palpable.
Drill a 1/8" hole in one of the end caps (Pic 2).
Cut the female end off the extension cable and strip off the outer covering about 2" in from the end of the cable (Pic 3).
Run the wire through the hole in the end cap and tie an overhand knot where the cable cover is still present.
Strip the red wire about 1/8" and tin it. Solder the red wire of the motor to the red wire of the cable. Fold a short piece of electrical tape over the solder joint to insulate it.
Cut the yellow wire (or braided shield if it has it) about 1" shorter than the red wire, strip it and tin the end of it. Solder the black wire from the motor to the yellow wire of the cable.
Ignore the third wire in the cable (if there is one).
Note: Use an ohm-meter to find which wire connects to the tip of the 1/8" plug and which wire connects to the shell of the plug if you are not sure which is which.
Cut a piece of thin foam that is 3/4" by about 3". Use enough foam to form a gentle fit between the motor and the inside of the tube. Tape the foam in place with some electrical tape (Pic 4).
Note: Be sure the weight at the end of the motor can rotate freely and is clear of the foam.
Slide the motor into the tube about 3/4 of the way so the rotating weight near the end. (A pencil is a good tool to help push the motor into the tube.) When the motor is positioned satisfactorily, glue it in place. (Put a dab of glue on the end of a small screwdriver and pat it in place near the motor from the wire end.)
Fold up the wires and tuck them into the tube. Slide the end caps on (Pic 1).
Test the vibra-tactile tip by plugging the plug in the jack on the relay box and toggling the SCR lock on and off. The vibra-tactile tip should vibrate actively when the SCR lock is on.
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. Consider making the haptic ino a wrist band so it can be worn and used hands-free. Consider a small tip that attaches to the headpiece, armrest or seat of a wheelchair. Perhaps the vibra-tactile motor could be included in a sip-and-puff mouth controller used by a paraplegic.
There is no reason the PCB, relay and vibra-tactile motor couldn't all be incorporated in one enclosure. These could all fit inside a keyboard for tactile reading while typing (see the next step for an example of this idea).
I have made a version with two tips that uses the two LEDs controlled by Mode 4 of the F-T-C software (Pics 1 and 2). Two tips, one for the dits and one for the dahs, can theoretically produce faster translation to Morse Code.
I added a button that connected two of the keyboard contacts on the PCB to simulate a space bar press (Pic 3). This let me read without constant keyboard actions.
The variations are almost endless so get to work and Feel-The-Code!