How to Build a Brain Controlled Wheelchair (Instructions Included)

This Instructable will show how to make a Brain-Controlled Electric Wheelchair, so that a person can become mobile without moving their body.

This could be useful for people who are paralysed, and are unable to control parts of their body enough to physically activate the joystick of an electric wheelchair. . Many people may be able to use this technology to gain some independence, and to take a break from needing an attendant to push their wheelchair so they can get some fresh air.

The parts of this system include an electric wheelchair, a laptop computer, an Arduino, an interface circuit, an EEG headset, and a collection of ready-made and custom software.

The software which was written specifically for this project (including the GUI and Arduino sketch) has been bundled with Puzzlebox Brainstorms, and is released freely under an Open Source license.

The EEG headset, which connects wirelessly to the laptop, allows the operator to simply think "forward" or "left" or "right" to cause the wheelchair to move.  Performance is related to practice by the user, proper configuration of the software, and good contact made by the EEG electrodes on the scalp of the operator.

The interface circuit connects between the Arduino's digital pins and the joystick of the wheelchair. . When the Arduino receives a command from the computer, it causes the circuit to "fool" the wheelchair into thinking that the operator has moved the joystick.

WARNING:  Electric wheelchairs are designed for trained operators who have practised manoeuvring safely.  Electric wheelchairs can weigh upwards of 200 pounds EMPTY!  They have no mechanism to stop when they hit a human or an animal, or go off a curb or down stairs or right through a bannister.  Make sure no one is in the path of a wheelchair which is not being operated by a human who can operate the OFF switch.  Make sure everyone in the vicinity of this Instructable realizes what may happen if they don't get out of the way.

Do not attempt to stop an electric wheelchair with your body.

 

To build this Instructable, you will need an electric wheelchair, (We used an Action Arrow Storm Series), an EEG Headset, (We used an Emotiv wireless headset),  a Laptop Computer, an Arduino, and an interface circuit made from basic electronics, (see step 5 for materials for the interface circuit).

The Electric Wheelchair was acquired as an unwanted extra from a local repair shop.  It was not considered serviceable for disabled persons because its condition was below standard.  If you hear of someone in need of an electric wheelchair who is low on funds, encourage them to ask repair shops for unwanted chairs.

The EEG Headset is an EPOC acquired from Emotiv.  Their site is here:
http://www.emotiv.com/ 

The Laptop Computer was Steve's but any laptop will do, it only needs to have two USB ports - one to connect to the Arduino, and the other for the EEG headset's Wireless receiver.

An Arduino is a small microcontroller platform with a USB serial interface.  In this case, it serves as a bridge between the laptop computer and the interface circuit (see steps 5 and 6).

Originally, the Arduino was not used, and the interface circuit was connected directly to the parallel port of the computer.  The computer we eventually used does not have a parallel port, so the Arduino performs the function of providing eight on/off signals based on a packet of serial data sent through its USB interface.  So if your laptop has a parallel port but is new enough to run the Emotiv software, you might be able to skip the Arduino.

 

The Software necessary includes the Puzzlebox Brainstorms BCI (Brain-Computer Interface) package which provides a GUI and visual feedback to the user and issues control commands to the Arduino hardware. Also required is the standard drivers and software included with the Emotiv EEG headset as well as an Aurduino Sketch which is a simple program written by us for an Arduino.

An optional Python-based backend control script can operate independently of the Puzzlebox Brainstorms GUI (see Step 7) and will translate keypresses entered on the keyboard into commands sent to the Arduino, which is connected to the interface circuit. The interface circuit makes the wheelchair move by simulating someone pushing on the joystick. This option is useful for controlling the wheelchair remotely via SSH session from another computer or device such as a mobile phone. The backend control script can be found here:
http://brainstorms.puzzlebox.info/tracker/browser/trunk/Puzzlebox/Brainstorms/Wheelchair_Control.py

And a suitable Python interpreter can be found here:
http://www.python.org/download 

The Puzzlebox Brainstorms software runs alongside the Emotiv headset'sControl Panel and EmoKey application, which allows the wearer of the headset to cause characters to be "typed" on the laptop when a learning algorithm matches the user's current brainwave patterns to previously trained sequences.These "typed" characters activate buttons displayed in thePuzzlebox Brainstorms GUI (or the backend control script) which tells the Arduino to activate the Interface Circuit which simulates someone pushing on the joystick, which causes the wheelchair to move.  The Puzzlebox Brainstormssoftware can be found here:
http://brainstorms.puzzlebox.info/static.php?page=downloads 

There are two programs from Emotiv which we will use for this project: Emotiv Control Panel and EmoKey. Both are available to download freely as part of their "SDKLite" software pack:
http://www.emotiv.com/store/sdk/edition/sdklite/ 

We were running the Microsoft Windows operating system because that is the most supported operating system by the Emotiv software at this time. (They are working on a Linux version)

The Arduino Sketch is a program which is loaded into the Arduino hardware using free software from the Arduino site.  The program watches for a series of characters coming in the USB serial port from the computer.  When it sees the letter "x" it watches the next eight characters that come through, and they correspond to eight pins on the Arduino.  If a character is "1" then that pin is set to ON, and outputs 5 volts, otherwise the pin is turned OFF and outputs zero volts.
The Arduino sketch can be found here:
http://brainstorms.puzzlebox.info/tracker/browser/trunk/arduino/puzzlebox_brainstorms_wheelchair_noisebridge/puzzlebox_brainstorms_wheelchair_noisebridge.pde

To load the above program into the Arduino, you need the Arduino software, found here:

You might also need drivers for the USB serial interface on the Arduino, depending on your operating system and which version of the Arduino you own.  Details at:
http://arduino.cc

The wheelchair will most likely use a pair of batteries the size of car batteries, and the same voltage.  These batteries are the most likely part of the wheelchair to present a problem.  If the chair has been unused for a long time, or if it was left in the "ON" position, the batteries might be totally ruined.

Otherwise, the batteries need to be charged.  A wheelchair has a charger connector, and should come with a charger with the same connector.  Keep in mind that the batteries are connected in series, which means that the two 12-volt batteries appear as a single 24-volt battery to the chair.  The charger must be a 24-volt charger, or a 28-volt regulated power supply.

Of course, you can also just use two ordinary car batteries, but they should be matched as to capacity and condition. . Ideally two identical brand-new batteries would be used.
It is possible to charge them individually with a 12-volt battery charger, but they should be charged equally since they will be cooperating to power the chair.

Some wheelchairs include reclining motors and other adjustments.  These systems usually have tilt sensors and other safety sensors which keep the chair from moving when it's not safe.  If the chair appears to turn on, but it won't move, check for this.

Also, chairs usually have a "clutch" which can disengage the wheels from the motors.  Sometimes this is a lever, and sometimes it's a lockable hub in the middle of the wheel.  There should be a sticker explaining clearly how to engage or disengage it.  If the clutch is released, the motors will not cause the chair to move, and they may not even turn if the wheelchair "brain" knows that they are disengaged.

Finally, there may be a manual brake.  Look for a sticker explaining how to operate it.  But most of the time, the brake is built into the motor, and is activated whenever the motors aren't turning.  In this type of chair, it will be impossible to push around if the clutches are engaged.  When the joystick is moved (and the chair is on) you will hear clicks as the brakes are released and the motors are engaged.  The brakes click back on when the chair stops after releasing the joystick.

If the batteries are charged, and the chair turns on and drives around, there is not much more to check.  Experiment with all of the switches you can find, to learn which are related to movement of the chair.  Our chair had two switches; one selects between OFF and LOW and HIGH speed, the other between DRIVE "A" and DRIVE "B" which are slow and fast.  It is necessary to know how to turn the chair OFF if it gets out of control.  It is useful to set the chair to its lowest speed when experimenting with computer control.

(Note:  we used an Action Arrow Storm Series electric wheelchair, with anAction MOC MK III motor controller.  The following instructions apply to the joystick for that system.  Other electric wheelchairs with different controllers may be similar or totally different.  Some chairs use an inductive joystick which is far too sophisticated for this hack!)

To control the wheelchair electronically, we need to make a connection to its joystick.  The joystick is a pair of variable resistors, one for forward/backward and another for left/right.  Each variable resistor is connected between two voltages; one approximately zero and the other around 12 volts.

This means that the center wire of each variable resistor is somewhere in the middle at rest, when the joystick is not being moved.  A circuit is necessary to pull current on these variable resistors when the Arduino's digital outputs cause it to do so.

In this wheelchair, the Joystick is a high-tech assembly where you can't see the actual variable resistors.  There are five wires coming out of the joystick, and two of them are the "middle terminal" of the forward/backward and left/right variable resistors.  We had to use a voltmeter and some head-scratching to figure out which wires these were (hence the electrical tape).

First we found Ground (usually the most prolific node on a circuitboard) and then we were able to measure the wires of the joystick while moving it around.  We saw that one wire changed up and down in voltage when the stick was pushed forward/backward and another one when the stick went left/right. These were the "middle terminal" of the two variable resistors in the joystick.

So we make a connection to the "middle terminal" of the forward/backward variable resistor, and another wire to the left/right one.  We also run a wire from Ground of the joystick circuit, and its 12-volt supply, which we found using the voltmeter.  These four wires run to a female pin-header connector like a CDROM drive audio cable uses.  This connector goes to a four-pin header on the interface board.

The interface board takes eight control lines in, from an Arduino or a PC parallel port, and can make the wheelchair think the joystick is being moved.  It does this using transistors, some diodes and a bunch of resistors.  All of these parts can be found at mouser.com or digikey.com or several other suppliers.  Since the transistors (2N7000) are FETs, they draw no current (although their default-mode resistors take a milliamp or so) so they can be driven from any digital control signal.  The diodes we used are 1N4148.

A datasheet for the 2N7000 transistor can be found here:
http://www.fairchildsemi.com/ds/2N/2N7000.pdf

The circuit contains eight transistors. Two of them pull the forward/backward wire toward ground through a resistor each. One has a larger resistor and the other a smaller one. When both transistors are turned on, both resistors are pulling toward ground, representing maximum speed in that direction.  Another two transistors are used the same way for the left/right wire.

The other four transistors are connected between ground and a resistor to the 12 volt power supply. These transistors are normally on, and their drain terminal is connected through a diode to the forward/backward or left/right wire. When these transistors are turned off, the resistor is no longer pulled toward ground and the joystick wire gets pulled toward the +12v wire through the diode.

This is an easy way to let an eight-bit TTL (0 / 5V diigtal) controller like the PC parallel port or 8 pins of an Arduino control the 12-volt analog wheelchair joystick. In actual practice (as you can see by looking at the schematic and the actual circuit) the resistor values have to be chosen to achieve values which will not cause the wheelchair brain to think there is a malfunction in the joystick. (the 41K and 6.8K resistors are to pull the transistors' inputs to their default state, so the joystick works normally when nothing is plugged into the interface boards' input side).

To determine resistor values, start with a variable resistor (a 100K-ohm is a good start) and connect a wire to its center and left terminal. With the wheelchair safely elevated to prevent movement (or with the operator safely in the seat with room to drive around) connect the variable resistor while taking notes. Start by connecting to the left/right wire and ground and with your variable resistor turned all the way to the right. (this is the highest resistance, 100K ohms).  A picture of a variable resistor is shown below.

When the left/right function is activated on a wheelchair, it rotates about its center like a tank.  Make sure your feet are safely in the stirrups or you could get hurt!

If the wheelchair does nothing, turn the knob left until the slowest speed desired happens. Disconnect the resistor, measure it with an ohm-meter, and write everything down (how it was connected and what the chair did). Do it again and find the lowest resistance and the highest speed desired and write that down. For this direction, you will need a resistor for each of the two transistors associated - one will be the value of the first test (slowest movement) and the other will be (get ready) the inverse of [the inverse of the value of the second test minus the inverse of the value of the first test]. This way, when both transistors are activated, the wheelchair sees the resistance of the second test. You can always just round up values if you don't have the exact right number. These resistors and the next two will go on the lower transistors in the schematic, to pull the joystick wire toward ground when those transistors are activated.

This test must be repeated with the forward / backward wire (you might go backwards at high speed). Take notes. After those two resistors are figured out, you will need to try the same tests but this time, connecting your variable resistor through a diode to the Red wire, which has +12 volts from the joystick circuit. Don't let this Red wire get shorted to ground, even for a second - you might FRY your electronics. The results of these tests will be the resistor values chosen for the upper transistors, which pull toward the red wire as you can see in the schematic.

Once you have determined the resistor values you want to use, or even before that, you can build the interface board.  We used "perfboard" and assembled it according to the same physical arrangement shown in the schematic image seen below, except that we used 8-pin machine sockets which work well for shoving resistors into, so that changes can be made to the speed of movement of the machine. You could also just use a bunch of 100K-ohm variable resistors....

Perfboard on WikiPedia:
http://en.wikipedia.org/wiki/Perfboard

The Gate terminal of each transistor goes to one of the eight control wires of the input cable. We used a DB25 Male connector since we were originally using a PC parallel port. The control wires are connected to pins 2 through 9, and ground to pins 18-25. We then had to make an adaptor to connect this to the Arduino when it replaced the parallel port in our setup.  You can skip the whole DB25 connector and just wire directly from the Arduino to the transistors on the interface board as long as you wire it up the right way, which is easier without the extra step anyway.

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