Part of Made in India,Design Innovation

Workshop,2015

A  Fresh  New  Experience  in  Project-­‐Making  &  Learning!

PHYSICS INVESTIGATORY PROJECT ON

TOUCH ACTIVATED SWITCH

What  if  your  body  becomes  a  part  of  the  circuit  and  a  current  is  passed  through  it?  Well,  you  can  do  this  using  a  touch  acFvated  switch  circuit.

In  this  project,  you  will  need  a  breadboard,  an  LED,  a  transistor,  a  resistor  and  a  few  connecFng  wires.  The  connecFons  were  made  such  that  a  wire  was  connected  to  the  base  of  the  transistor  and  another  wire  was  connected  to  the  Vcc  (posiFve/high  voltage).  The  other  ends  of  both  the  wires  were  leP  open.  It  was  observed  that  when  the  two  connecFng  wires  were  pressed,  the  LED  glows.    The  harder  you  press  it,  the  more  will  be  the  intensity  with  which  the  LED  glows.  Now,  the  voltages  across  the  base-­‐emiQer  juncFon  and  the  collector-­‐emiQer  juncFon  were  measured  using  a  mulFmeter.  It  was  found  that  that  the  voltage  at  the  base  was  greater  than  the  voltage  at  the  collector  which  verified  that  the  transistor  

was  in  the  saturaFon  state  and  acted  as  a  switch.

The  reason  why  the  LED  glows  is  because  our  body  acts  as  a  part  of  the  circuit  when  we  hold  the  wires.  It  offers  a  resistance  in  the  base-­‐emiQer  circuit,  the  value  of  which  may  vary  between  40,000  Ω  to  1,000,000  Ω.    When  the  wire  is  pressed  harder,  the  area  of  contact  with  the  connecFng  wires  will  increase.  Consequently,  the  effecFve  resistance  offered  by  our  body  decreases  and  the  current  increases.    This  makes  the  base-­‐emiQer  juncFon  forward  biased,  due  to  which  a  small  current  flows  through  the  transistor.  The  transistor  is  in  the  saturaFon  region  and  acts  as  a  switch.  As  a  result,  its  collector  and  emiQer  juncFon  is  approximately  equal  to  zero  volts.  A  collector  current  flows  in  the  collector-­‐emiQer  circuit.  The  current  gets  a  closed  path  and  the  LED  glows.  

Have  a  look  at  what  we  provide  in  our  Project  Kit!

CoolJunk   is   India's   fastest   growing  DIY   (do-­‐it-­‐yourself)   kits   company   focused   on   project-­‐based   learning   in  science,   engineering   and   technology.  Having   20,000   users   in   India,  US,   Singapore,   Middle   East   and   New  Zealand,  the  CoolJunk  kits  are  known   for  quality,  innovaFon   and  high  producFon  value.  CoolJunk  has  been  featured   in   naFonal   and   internaFonal   journals   including   Wallstreet,   Yourstory,   Hindu   Business   Line,  NextBigWhat  and  was  tagged  as  the  coolest  Indian  start-­‐up  in  IAN  Bootcamp-­‐2011.  

You  may  also  refer  to  the  video:  Touch  Ac?vated  SwitchFor  more  projects  visit  our  website:  CoolJunk  

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