This document describes work on developing puppets that can playback recorded voices modulated by the movement of their mouths. It discusses two approaches: 1) capacitive sensing using a loading mode circuit to detect mouth movements and 2) using electric field sensing with a transmit-receive circuit to track mouth movements over a larger range. The loading mode approach could only detect small movements while the transmit-receive approach is still being developed and tested. The goal is to use the amplitude and speed of mouth movements to control the volume and playback speed of a pre-recorded voice.

1. PUPPETS WITH VOICES
NATALIE FREED
MAS 836
SPRING 2011
Thursday, August 25, 2011

2. APPLICATION
PICK UP A PUPPET AND MOVE ITS MOUTH TO PLAY BACK YOUR
RECORDED VOICE.
EACH PUPPET HAS ITS OWN VOICE, MODIFYING YOUR OWN.
IT SHOUTS IF YOU MAKE BIG MOUTH MOVEMENTS, WHISPERS IF
YOU MAKE SMALL ONES.
SPEED OF MOUTH MOVEMENT CHANGES SPEED OF PLAYBACK
Thursday, August 25, 2011

3. APPROACHES
1. CAPACITIVE SENSING - LOADING MODE
2. ELECTRIC FIELD SENSOR / CAPACITIVE SENSING -
TRANSMIT-RECEIVE
Loading Mode (measure I )
• Single Electrode
• No cable to electrode
• No contact with electrode
• Couples to everything • 3-object geometry
• Hard to adjust sens. area => Hard to do tracking
• Used for everything • Can focus w. tomograpy
- Stud finders (pre MIR) => Add more transceivers
Theremins, buttons...
REFERENCES [1]
Thursday, August 25, 2011

4. LOADING MODE
CIRCUIT
LOADING MODE
RELAXATION OSCILLATOR + VOLTAGE
FOLLOWER + BUFFER WITH OFFSET
Thursday, August 25, 2011

5. LOADING MODE
BUILD PROCESS
IRONING FUSIBLE CONDUCTIVE FABRIC TO THICK FELT
Thursday, August 25, 2011

6. LOADING MODE
BUILD PROCESS
GROUND SENSING SHIELDING
ELECTRODE
Thursday, August 25, 2011

7. LOADING MODE
BUILD PROCESS
SEWING LEADS TO ELECTRODE, SHIELDING, AND GROUND
Thursday, August 25, 2011

8. LOADING MODE
BUILD PROCESS
SEWING SENSORS INSIDE THE PUPPET
Thursday, August 25, 2011

9. LOADING MODE
RESULTS
ONCE HAND IS IN PLACE, RANGE IS TOO SMALL
(ABOUT 2 INCHES) AND OUTPUT IS NOT LINEAR.
EFFECTIVELY MEASURES VERY SMALL
MOVEMENTS (FROG PUPPET) BUT NOT LARGE
(WHALE PUPPET).
Thursday, August 25, 2011

10. TRANSMIT/RECEIVE
CIRCUIT
transimpedance
amplifier
(inverting) active high pass
filter with
10 pF
amplification
(inverting)
1M
Ohm
transmit receive 0-500KO
electrode electrode VCC hms
VCC envelope
LC circuit follower
-
125kHz
pulse
tuning cap
+ 20K
-
TLV2374 Ohms
6.8 nF
+ TLV2374
ATMEGA32 ~47pF
6.8 nF
1M
Ohm
U4
(Teensy) VCC
5K
ADC Ohms
Vbias =
2.5V
5K
Ohms
1. 125kHz 0 to 5V square wave from ATMEGA to 100V PTP sine wave from resonant circuit.
2. output of transmit electrode received as current on receive electrode.
3. transimpedance amplifier turns current into changing voltage signal
4. high pass filter with (adjustable) amplification reduces noise, raises level to 0-5V for ADC
5. envelope follower turns signal into DC voltage for ADC to read
Thursday, August 25, 2011

11. TRANSMIT/RECEIVE
MICROCONTROLLER CODE
Using Teensy (ATMEGA32 U4) but can’t use Arduino compiler because it hogs the timers! The
square wave ends up looking like this:
Instead, use just C/AVR and turn off the other timers, this fixes it.
Use 16-bit timer/counter 1 to generate square wave:
ISR(TIMER1_OVF_vect)
{
TCNT1=0xFFD9; // set initial timer/counter value (16 bit counter)
PORTB ^= _BV(PORTB2); //toggle pin B2
}
Thursday, August 25, 2011

12. TRANSMIT/RECEIVE
BUILD PROCESS
Op-Amp test board on breadboard
(beware when moving breadboard to
protoboard, changes in capacitance)
vinyl-cut electrodes
Pockets to hold boards in correct
Round protoboards from Radioshack alignment to each other and make
boards removable
Thursday, August 25, 2011

13. TRANSMIT/RECEIVE
RESULTS
HTTP://VIMEO.COM/28166293
Thursday, August 25, 2011

14. SOFTWARE
(WORK IN PROGRESS)
Thursday, August 25, 2011

15. SOFTWARE
P-TO-P AMPLITUDE OF OSCILLATION OF PUPPET MOUTH
AFFECTS GAIN. WHICH PUPPET IS CHOSEN AFFECTS PITCH.
Thursday, August 25, 2011

16. RESOURCES
1. CAPACITIVE SENSING/ELECTRIC FIELD SENSOR LECTURE NOTES, JOE
PARADISO (HTTPS://STELLAR.MIT.EDU/S/COURSE/MAS/SP11/MAS.836/
COURSEMATERIAL/TOPICS/TOPIC1/LECTURENOTES/CLASS6-
EMSENSORS/CLASS6-EMSENSORS.PPT)
2. TEENSY REFERENCE - PJRC (HTTP://PJRC.COM/TEENSY/)
3. FABFISH (HTTP://BDM.CC/FABFISH/)
4. FILTERS/AMPLIFIERS REFERENCE (HTTP://WWW.ELECTRONICS-
TUTORIALS.WS/FILTER/FILTER_6.HTML)
5. ATMEGA TIMER/COUNTERS (HTTP://WWW.ELECTRONICSBLOG.NET/
EXAMPLES-OF-USING-ARDUINOATMEGA-16-BIT-HARDWARE-TIMER-FOR-
DIGITAL-CLOCK/
MANY THANKS TO: BRIAN MAYTON, MARK FELDMEIER,
DAVID CRANOR, NAN-WEI GONG
Thursday, August 25, 2011

17. Thursday, August 25, 2011