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BUILD A BIOFEEDBA MONITOR FOR YOUR PC By JIM BARBARELLO Feeling tense? Build this simple biofeedback monitor and let your computer calm you down. It can be used with any IBM PC-compatible computer. And if you don't need biofeedback, it is an interesting exercise in computer interfacing. Although most people think of the IBM PC primarily as a business computer that grinds away from 9 to 5 through spreadsheets, databases and documents, it can also be made to serve other, quite different roles. One such application is as a computer-assisted biofeedback monitor. Biofeedback is the process of monitoring a biological function that indicates your level of tenseness, and then feeding back that information to you in real time. By allowing you to see what happens when you try to relax, biofeedback lets you discover the techniques that work best for you. You can then practice those techniques to gain more control over daily tension and stress. One biological function that indicates tenseness is your galvanic skin response, usually called simply GSR, which in non-medical terms means the resistance of your skin. PROBE A 10k 3 PROBE B PLUG 1 11 IC1 7555 16 l 3V .!.. 20 As you become more tense, your rate of perpiration increases, thereby lowering the resistance of your skin. As you become less tense - as you "calm down" - the perspiration rate slows and your skin's resistance increases. A variation from your normal or average GSR is therefore an accurate biofeedback indicator of how tense or calm you are at a given instant in time. The easiest way to measure GSR would be with an analog resistancemeasuring device such as an ohmmeter (or your multimeter switched to an Ohms range). Unfortunately, analog measurements are not wellsuited to digital computers. There is, however, a surprisingly simple alternative. By using a circuit that generates a digital pulse with a duration proportional to a resistance, we can use a computer to measure the length of the pulse and then interpolate the pulselength into a resistance value. That approach forms the basis for this BIOFEEDBACK MONITOR Fig.1: the circuit uses a 7555 timer IC that's triggered by the INIT line (pin 16) of the computer's printer port. 38 SILICON CHIP Copyright 1988, Gernsback Publications. Reprinted with permission from October 1 988 " Computer Digest". ---20 0000 0000 I 1 S..!_r+t' 0 I 3V BATTERY Fig.2: the circuit can be quickly wired up on a small piece of Veroboard. The two probes are actually aluminium foil strips which are fixed to the lid of the case using double-sided tape. biofeedback monitor for IBM PCcompatible computers. The monitor's schematic is shown in Fig.1. IC1 is a CMOS 555 timer which is wired as a simple pulse generator. The width of its output pulse is the product of capacitance Cl, resistance R1, and the skin resistance present between probes A and B. Since Cl and R1 are constant, any change in the pulse width is the direct result of a change in the resistance between the probes. Now all we need to do is to trigger IC1 to force its output at pin 3 high and measure the periorl of time until the output on pin 3 goes low (ie, returns to ground). nector, the INIT line, connects to IC1 's trigger input, pin 2. Sending out a short INIT pulse from the computer triggers IC1 and causes IC1 's output, pin 3, to go high. Pin 3 goes low at the end of the pulse (ie, when Cl has charged to 2/3Vcc). Pin 11 of PL1 is the computer's BUSY line. If we have the computer check for a low on pin 11, it will know when IC1's pulse has ended. The common ground between the computer and the biofeedback monitor is through PL1 pin 20. Switch S1 applies power to the circuit from series-connected batteries B1 and B2. The batteries provide only 3 volts, so the output of IC1 will also be about 3 volts peak instead of the more usual 5 volts. Although 3 volts is much less than 5 volts, it is high enough to be sensed by the computer's printer port. The software The simplicity of the hardware is made possible by the fact that the software does most of the work in creating a screen display of your GSR. Let's look at some of the more important aspects of the program, called PCBIO (for PC Biofeerlback), as shown in Listing 1. Line 30 looks to see if a printer port is installed and determines its address. Line 50 uses that information to set the address for the trigger input (T) and output (G) to the circuit. Line 190 begins the process of initialisation. Since each person's GSR is different, the program takes five in- The printer port It may seem strange but the computer's LPT1 parallel printer port is the ideal way of interconnecting the biofeedback monitor to the computer. The PC's printer port has a number of input and output lines that are normally used to do things like initialise the printer and check for a busy status. In our circuit, a 25-pin (DB25 male) connector PL1 attaches to the PC's printer port. Pin 16 of the con- Fig.3: when you load the PCBIO program into your computer the opening screen shows a thermometer-type display that ranges from calm to tense. MAY1989 39 Fig.4: if you're tense, the indicator will move up the display and the tone from the speaker will increase in pitch. itial samples and averages them to determine a mid-range value [Y in line 220). Line 220 also calculates an increment value [INC) which is used to determine the range from full calm to full tense. Those range values are stored in array L in line 230. The actual monitoring process begins in line 250. A call to the subroutine at line 320 gets a sample from the hardware as a count stored in variable X. Lines 280 and 290 determine where the tenseness indicator should be and places it there. The monitoring session ends when either full calm is reached (L ) 22 in line 280) or when you press the ESC key during monitoring (C = 27 in line 260). The subroutine at line 320 interfaces with the hardware. Line 330 generates a short negative-going pulse to trigger IC1. Line 340 begins counting the time by incrementing variable X and checks to see if ICl 's output has returned to zero [INP(G) = 127). When it does, line 350 checks to see if another sample should be taken [Z ( XF). Variable XF is a scaling factor used to ensure that the count returned in variable X will always be above 100 [lower counts make the gauge displayed on the screen respond too quickly, and are distracting during the monitoring session). The commands LOCATE 1,60:PRINT X;: in line 350 display the actual count number just past the title -on the screen display. 40 SILICON CHIP Fig.5: the calmer you get, the lower the indicator's position and the lower the tone from the speaker. Construction The circuit can be assembled on a small piece of Vero board which is installed, along with a battery holder, in a small plastic utility case. Simply pass the component leads through the appropriate holes in the Veroboard [see Fig.2) and solder them to the copper strips. An oversize drill can be used to make the necessary cuts in the copper pattern. Glue the battery holder into the case as close as possible to one end. If you'd like to secure the circuit board, it too can be glued to the PARTS LIST 1 plastic utility box, 83 x 54 x 28mm 1 piece of Veroboard 1 SPOT miniature toggle switch 1 D825 male plug 1 double-AA battery holder 1 battery snap connector 2 AA-size 1 . 5V batteries 1 7555 or TLC55 CMOS timer IC (IC1) 1 1µ,F metallised polyester capacitor 1 10kQ 1/4 W resistor 2 solder lugs 2 3mm x 6mm-long screws plus nuts and washers 2 metres of 4-way telephone cable 1 small cable tie 2 pieces of cooking foil, 4.5 x 2cm case with a drop of silicon rubber adhesive or Blue-tak. The finger contacts are simply two aluminium foil strips fixed to the cover with double-sided tape. These are then connected to the circuit via machine screws which pass through the lid and the foil. Cut two strips of ordinary household aluminium foil to a size measuring 4.5 x 2cm. Apply doublesided tape to the dull side· of the foil strips then carefully affix them to the lid of the case. Now drill two 3mm-diameter holes in the locations shown in the photos. Place two 3mm x 6mmlong screws through the holes and secure each one using a solder lug, washer and nut. The probe leads from the PC board can then be soldered to the solder lugs. We used a length of 4-wire (2 pair) phone ea ble to connect the circuit to the DB25 male connector. A plastic cable tie was used to anchor the cable inside the case. Testing the circuit Before you hook the circuit to your computer, it is a good idea to test the circuit on the bench. The easiest way to do this is to connect a jumper wire between pins 2 and 6 and a lOOkQ resistor across the screw terminals for the finger contacts. This allows the circuit to operate as an oscillator instead of a pulse generator. If you have an oscilloscope you can then check that the circuit is oscillating. Connect the oscilloscope probe between pin 1 [OV) and pin 7 and you should see a sawtooth waveform. Alternatively, if you don't have access to an oscilloscope you can use your multimeter to check the circuit. Connect_ pins 2 and 6 as before but omit the lOOkO resistor. Then connect the multimeter, switched to a low DC voltage range, between the two finger contacts. With the circuit running, the meter should read half the supply voltage; ie, about 1.5V for a 3V supply. Having checked the circuit, remove the connection between pins 2 and 6 and then plug the DB25 connector into your computer's printer port. Using the monitor Connect PLl to your computer's parallel printer port, apply power to the biofeedback monitor by closing S1, then load BASIC and the PCBIO program into your computer. When you run the program, the computer will create the screen shown in Fig.3. In the centre is the tenseness gauge resembling a thermometer. The top of the gauge is maximum tenseness, the bottom of the gauge Fig.6: you will probably already have most of the parts for this project in your junkbox. Take care - it's easy to make a mistake with Veroboard. Fig. 7: the circuit is connected to the computer's parallel printer port via a DB25 male plug. Listing 1 1 REM** PC Biofeedback Monitor Program 2 REM** NAME: PCBIO 3 REM** c 1987, JJ Barbarello, Manalapan, NJ 07726 4 REM** V870911 10 CLEAR:DEFINT G,X:G=O:X=O:DEFSTR A,B:A=CHR$(232):B=SPACE$(2) 20 COLOR 0,6,6:CLS:KEY OFF:WIDTH 80:DIM L(22) 30 DEF SEG=64 :PA=PEEK(8)+256*(PEEK(9)) 40 IF PA=O THEN COLOR 7,0,0:CLS:GOTO 430 50 A=CHR$(232):B=SPACE$(2):G=PA+1 :L=13:T=PA+2:LOCATE 1,23,0 60 PRINT STRING$(5, 16);" P.C. BIOFEEDBACK MONITOR " ;STRING$(5, 17) 70 LOCATE 2,37:PRINT CHR$(201 );STRING$(5,205);CHR$(187) 80 FOR 1=3 TO 22:LOCATE I,37:PRINT CHR$(204);B;A;B;CHR$(185):NEXT 90 LOCATE 23,37:PRINT CHR$(200);STRING$(5,205);CHR$(188) 100 LOCATE 3,31 :PRINT "TENSE " ;CHR$(206) 110 LOCATE 13,29:PRINT "AVERAGE " ;CHR$(206) 120 LOCATE 22,32 :PRINT "CALM ";CHR$(206):PLAY "L64" 130 FOR 1=3 TO 22:LOCATE I,40:PRINT" " :P$="N"+STR$(60-I*2):PLAY P$:NEXT I 140 FOR 1=22 TO 13 STEP -1 :LOCATE I,40:PRINT A:P$="N"+STR$(60-I*2) 150 PLAY P$:LOCATE I,40:PRINT" ": NEXT l:LOCATE 13,40:PRINT A 160 LOCATE 24 ,22 ,1:PRINT "Press (ENTER) to begin, or (ESC) to end ... "; 170 AA=INPUT$(1):C=ASC(AA):IF C=27 THEN 400 ELSE IF C013 THEN 170 180 LOCATE 24,22,0:PRINT SPACE$(42); 190 LOCATE 24,34:PRINT "INITIALIZING ... "; :Y=0:PLAY"L64" :XF=1 200 GOSUB 320:IF X( 100 THEN XF=XF+ 1:PLAY "L64;N32":GOTO 200 210 FOR 1=1 TO 5:GOSUB 320:PLAY "L64 ;N34": Y=Y+X:NEXT I 220 Y=Y/5 :INC=Y/100:LOCATE 24 ,28:PRINT"Press (ESC) to End Trial."; 230 PLAY"L32" :LOW=Y-10*INC:FOR 1=3 TO 22:L(l)=LOW+(l-2)*INC:NEXT 240 REM** MONITORING 250 P$="N"+STR$(60-(L *2)):PLAY P$ :IF X=O THEN 360 260 AA=INKEY$:IF AA()<'" THEN C=ASC(AA):IF C=27 THEN 370 270 GOSUB 320 280 IF X)L(L) THEN LOCATE L,40:PRINT" " :L=L+1:IF L)22 THEN 370 ELSE LOCATE L,40:PRINT A 290 IF X(L(L) THEN L=L-1 :IF L(3 THEN L=3 ELSE LOCATE L+1,40:PRINT " ":LOCATE L,40:PRINT A 300 GOTO 250 310 REM** SAMPLING SUBROUTINE 320 X=O:Z=O 330 OUT T,O:OUT T,4 340 X=X+1:IF (INP(G) AND 128)=0 THEN 340 350 Z=Z+1 :IF Z(XF THEN 330 ELSE LOCATE 1,60:PRINT X;:RETURN 360 REM** TRIAL END 370 LOCATE 13,8,1 380 PRINT "TRIAL COMPLETED. Press (ENTER) to try again, or ( ESC) to end ... " ; 390 AA=INPUT$(1 ):C=ASC(AA):IF C=13 THEN CLS:GOTO 50 ELSE IF C027 THEN 390 400 COLOR 7,0,0 :CLS:LOCATE 10,28 ,1:PRINT"MONITORING SESSION OVER" 410 LOCATE 13,1:END 420 REM** CAN'T FIND STANDARD PRINTER PORT 430 LOCATE 10,27,1:PRINT''PRINTER PORT 1 NOT AVAILABLE" :PRINT:PRINT:END MAY 1989 41 sure that the unit is working properly, you can begin actual monitoring. You should try to concentrate on different images or thoughts and note the results on the gauge. At first it may seem that trying to calm down actually increases tension. That is normal because the untrained mind tends to race through many different thoughts. Through practice you will learn how to focus on the images and thoughts that actually decrease tension, disregarding everything else, and use them to assist you in the calming process. Tweaking Fig.8: the completed prototype. Notice how the leads to the foil strips connect to the screws that pass through the lid of the case. is maximum calm, and the centre of the gauge is average. The message on the bottom of the screen asks you to press ENTER to begin monitoring, or ESC to end the session. The room you're in should be comfortable (about 20°C). Sit in a chair that provides good support and place the biofeedback monitor next to you on a table or stand that can support your forearm. Make sure your fingers are free of oil or excess perspiration. Rest your forearm on the stand in front of the unit, place your first (index) finger on one probe and your second finger on the other probe. It is very important that you do not move your fingers or change the pressure on the probes during the monitoring session, as that will change the resistance between the probes and give a false reading. Press the Enter key with your free hand. The message on the bottom of the screen will change to "INITIALISING" and you will hear a series of beeps as the system measures your initial level of tenseness. After a short time, the message on the bottom of the screen 42 SILICON CHIP will change to ''Press C to End Trial"; you are now monitoring your changing level of tenseness. That's indicated by the moving cursor in the middle of the gauge and a beep with a changing tone. As you become more tense, the beep frequency will increase and the indicator will ascend, as shown in Fig.4. When you calm down, the beep frequency decreases and the indicator descends as shown in Fig.5. The session ends when you either press the ESC key or reach maximum calm (nirvana?). The mes~age "TRIAL COMPLETED. Press Enter to try again, or Escape to end" will appear in the middle of the screen. When you end the session, the screen will clear except for the message "MONITORING SESSION OVER". To test the unit, begin monitoring. Press down hard with your two fingers to simulate increased perspiration (tenseness). The indicator should begin to rise. Release the pressure and note that the indicator begins to fall. Press ESC to end the trial. When you are The software monitoring subroutine is sensitive to the speed of your computer. The program listing contains the fact "IF X( 100" in line 200 to adjust it for use on a standard 4.77MHz computer. Computers operating at 8MHz or AT systems will respond more quickly and produce a higher count for the same amount of time and thus seem to be racing along. To compensate for racing, simply change the "100" in line 200 to a higher number (try 300 as a starting value and adjust it until you are comfortable with the speed). Closing thoughts The biofeedback monitor is basically just a self-learning type of device that also happens to be a lot of fun. It is not meant to take the place of any necessary medical treatment or equipment. However, with practice, the device can help you learn how to reduce everyday stress and tension. Sooner or later you'll find that you do have the ability to mentally calm and relax yourself. Another interesting point is that GSR is one measure that is used by polygraphs (lie-detectors) to determine whether or not someone is telling the truth. For that reason, the device can also be used as a rudimentary "lie detector" for entertainment at parties and gatherings. And even if you don't put much store in this device as a biofeedback monitor, we are sure that it will be the basis for many interesting computer applications. ~