NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

Bioelectrical  Signals  &  Systems  

Laboratory  Exercise  for  the  Bioelectricity  Module  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

 •  In  this  laboratory,  students  will  measure  and  analyze  bioelectrical  signals  

received  from  an  opAcal  pulse  sensor.     It  has  been  noted  in  the  ENFUSE  bioelectricity  module  that  a  pulse  signal  from  the  heart  can  be  displayed  as   an   analog  waveform   change   in   voltage.     For   every   pulse,   the   sensor  experiences  a  rise  (peak)  in  the  voltage  signal.    The  signal  then  falls  to  a  normal  state.    There  is  a  charging/discharging  that  follows  an  exponenAal  form  for  the  voltage.        

Laboratory  Overview  

hLps://docs.google.com/document/d/1FVFffuKD9OnkTOwxs3dVaxp5LYb4S1aj65MS6lvI

ZbA/edit?hl=en_US  

•  To   demonstrate   these   concepts,   students  will   use   a   pulse   sensor   to   generate   a  bioelectrical   signal   (waveform).    This  signal  will   be   displayed   on   an   oscilloscope   for  analysis.   In   addiAon,   students   will   build   a  filter   using   selected   resistors   and  capacitors.    Any  change  in  the  signal  due  to  filtering  will  be  observed  and  recorded.        

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

 Using   a  UA   741  Op-­‐Amp,   set   up   an   inverAng   amplifier   using   a   100  Ω   source  resistor  and  a  1  kΩ  feedback  resistor.    Use  +10  VDC  for  Vcc+  and  -­‐10  VDC  for  Vcc-­‐.    See  next  slide  for  schemaAc.    §  Q1:  What  do  you  expect  for  closed-­‐loop  gain?  

For   your   signal   source,   set   the   funcAon   generator   for   a   1   kHz   sinusoid   with  amplitude  0.1  V.    Use  Channel  1  of  the  oscilloscope  to  monitor  the  input  signal  and  Channel  2  of  the  oscilloscope  to  monitor  the  output.    •  Q2:  Sketch  and  discuss  what  you  are  seeing  at  the  input  and  output  on  the  

oscilloscope.    Why  is  this  what  you  did  (or  did  not  )  expect?    

But  First,  An  Op-­‐Amp  Exercise    

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

InverAng  Amplifier  Circuit  

Bioelectrical  Signals  &  Systems  

1  kΩ  

100  Ω   -­‐    +  

0.1  cos  (2π  1000  t)  V  Vout  

feedback  

2

36

UA741  Op-­‐Amp  pin  4  to  Vcc-­‐  pin  7  to  Vcc+  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

Replace   the  1  kΩ   feedback   resistor  with   the  100  kΩ  potenAometer   found  on  the  Knight  Mini-­‐Lab  staAon  (be  sure  to  turn  off  the  power  before  disassembling  the  circuit).    Adjust  the  potenAometer  unAl  the  output  signal  is  10  x  the  input  signal.    Power  down  your  circuit  and  measure  the  resistance  across  the  potenAometer.    §  Q3:  What  was  measured?    Is  this  what  you  expected  (and  why)?  

Reconnect   the  potenAometer   and   increase   its   resistance  observing  what   you  see  on  the  oscilloscope  (you  may  need  to  change  scale  on  CH  2).    §  Q4:  What  do  you  observe  as  the  potenAometer  reaches  its  maximum  value  

of  resistance?    Sketch  the  output  waveform  and  discuss  what  is  happening.    

An  Op-­‐Amp  Exercise  ConAnued    

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

Pulse  Sensor  Exercise  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

 Equipment  &  Parts  Oscilloscope        Pulse  Sensor  Amped  (to  be  assembled)  Leads  (1  posiAve,  1  negaAve)    5.6  kΩ  Resistor  Power  Supply        10  μF  Capacitor  Breadboard        Glue  gun  (1  glue  sAck)  1  cm  x  1  cm  piece  of  tape      Nail  trimmer    OpAonal  Equipment  if  using  Pulse  Monitoring  Sopware  Arduino  UNO        9V  BaLery    

Pulse  Sensor  Laboratory  Materials  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

Assemble  the  pulse  sensor  amped  per  the  following  website      hLp://pulsesensor.myshopify.com/pages/code-­‐and-­‐guide  and  download  the  Pulse  Sensor  Ge4ng  Started  Guide  from  the  download  archives.  

 Front  side      Back  side  

 Do   not   touch   the   front   side.   From   this   guide,   you  will   be   asked   to  place   the   vinyl   protector   disc   over   the   front   side   to   protect   the  photodiode;   then  you  will  use  the  glue  gun  to  coat   the  back  side  to  protect  the  circuitry  and  the  cables;  let  the  glue  dry  and  connect  the  Velcro  disc  to  back  side  and  strap  to  complete  assembly.  

Sensor  Assembly  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

Pulse  Sensor  Circuit  

hLps://www.circuitlab.com  

Bioelectrical  Signals  &  Systems  

Light  Source  Detector   RC  Filtering  

Resistors  for    Closed-­‐Loop  Gain  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

1.  Set  the  power  supply  to  a  +5V  source.  2.  Turn  on  the  oscilloscope    3.  Connect  the  breadboard  power  +5V  and  Ground  (GND)  sources  4.  The  pulse  sensor  can  now  be  connected  to  the  bread  board  with  

the  following  connecAons:  •  RED  wire  =    +5V  •  BLACK  wire  =  GND  •  PURPLE  wire  =  Signal  to  Oscilloscope      Before  checking  your  pulse,  verify  that  your  pulse    sensor  is  working  by  turning  on  the  power  source.  The  front  side  LED  should  turn  on  green  to  indicate  it  is  working.  

Laboratory  Procedure  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

SchemaAc  of  Breadboard  Setup  

hLps://www.circuitlab.com  

Filtered  Signal,  Vout  (Channel  2)  

Unfiltered  Signal  Output  (Channel  1)  

Vout  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

5.  An  unfiltered  (CH  1)  and  filtered  (CH  2)  pulse  signal  can  be  measured  on  the  oscilloscope  using  the  below  breadboard  set  up  

Image  of  Breadboard  Setup  

GND  

+5V  Source  

Unfiltered  Signal  Output  

(Channel  1)  

Filtered  Signal  Output  

(Channel  2)  

Pulse  Sensor  

RC  filter  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

6.    Wrap   the  pulse   sensor  around   your   finger   (or  aLach   to   your   earlobe).    You  should  receive  a  signal  of   the   same   waveform   as  presented   right.     This  example   uses   a   low   pass  filter   designed   to   cancel  noise  above  ~3  Hz  using  a  10  μF  capacitor  and  5.6  kΩ  resistor,   and   capacitor.    The   green   signal   is   the  filtered   response   (Channel  2).  The  yellow  signal  is  the  u n fi l t e r e d   r e s p o n s e  (Channel  1).    

Signal  Analysis  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

Connect  CH  1  and  CH  2  to  the  unfiltered  and  filtered  sensor  outputs,  respecAvely.    §  Q5:     Without   your   finger   placed   on   the   sensor,   what   differences   do   you  

observe  between  the  two  outputs?    Discuss.  

ALach  the  probe  to  a  finger  or  earlobe  (don’t  press  Aght)  and  note  the  response.    §  Q6:     Sketch   the   filtered   waveform.     What   is   the   minimum   and   maximum  

voltage   noted?    What  DC   offset   is   noted?  How  does   the   filtered  waveform  compare  to  the  unfiltered  waveform?  What  is  the  pulse  rate?  

Replace  the  5.6  kΩ  resistor  with  a  56  kΩ  resistor  .    §  Q7:    How  do  the  unfiltered  and  filtered  waveforms  compare?  

Discussion  QuesAons  

Bioelectrical  Signals  &  Systems  

NAU·∙UH·∙UM·∙USF·∙UVM·∙·∙NSF  

Replace  the  56  kΩ  resistor  with  a  560  kΩ  resistor  .    §  Q8:    How  do  the  unfiltered  and  filtered  waveforms  compare?  

§  Q9:  Discuss   in   terms  of   transfer   funcAon  and   in   terms  of  RC  Ame  constants  what  is  happening  as  the  resistor  size  increases  and  how  and  why  this  change  impacts  the  measured  signal.  

§  Q10:  Using  op-­‐amps  along  with  acAve  and/or  passive  filtering,  design  a  circuit  that   would   increase   the   voltage   of   the   pulse   component   of   the   signal   but  block  any  DC  offset.    What  other  system  might  this  circuit  be  applied  to?  

Discussion  QuesAons  ConAnued  

Bioelectrical  Signals  &  Systems