Digital Microfluidics Control System II
P15610
Phase One: Problem Definition
Problem Statement
Previous state - The previous control system is not self contained
and uses a class AB amplifier which makes the system large and
nonmodular.
Desired state - A fully enclosed control system that efficiently
operates the DMF chip while providing accurate feedback.
Project Goals - Make key improvements to functionality of control
system, and complete all assigned deliverables.
●
●
Repeatable, consistent droplet motion.
Durable, lightweight, modular design.
Constraints - Use provided DMF chip, control fluid droplets using
electrowetting, use DI water as test fluid, ensure compatibility
with peripheral hardware and GUI.
Phase One: Problem Definition
Engineering Requirements
Phase One: Problem Definition
DropBot
Phase One: Problem Definition
Functional Decomposition
Phase Two: Subsystem Identification
System Layout
Phase One:
Problem
Definition
Morphological
Chart
Phase Two: Subsystem Identification
Original CAD Models
Phase Two: Subsystem
Identification
Original External Design
Components:
3 Enclosures and Lid
1 Fan and Fan Guard
Electrical Ports: USB, BNC, 40 pin connector, Power
Vent Grommets
Phase Three: Design and Testing
Output Board: PCB layout
Phase Three: Design and Testing
Output Board: PCB layout
Phase Three: Design and Testing
Output Board: Functionality
● Takes amplified signal from amplifier chooses which pin
on DMF chip to apply high voltage
● Consists of:
o HV Solid State Relays
o Shift Registers (Load pin positions to apply voltage
to)
o Control Mechanism (ATMEGA)
Phase Three: Design and Testing
Output Board: Functionality
ATMEGA
Shift
Register
40 HV Relays
Shift
Register
Off
Board
DMF
Chip
Phase Three: Design and Testing
Input Board: Functionality
Phase Three: Design and Testing
Input Board: Functionality
1pF: steady state voltage
of 29mV
200pF: steady state
voltage of 5.00V
Rise time: <10ms
Phase Three: Design and Testing
Input Board: Functionality
60pF: steady state
voltage of 1.693V
61pF: steady state
voltage of 1.720V
Granularity: 27mV/pF
or: 5.5 qlevel/pF
Phase Three: Design and Testing
Input Board: Functionality
-Total simulated current draw: <25mA
-Noise: input filter to buffer limits frequency generator noise
-Large capacitive loading: Zener diode limits output (below)
-Output noise: two-stage
low-pass filter
Phase Three: Design and Testing
Input Board: Previous Data
-Absolute values of measured
capacitances ranged from 30pF to
170pF
-Capacitance changes over time in the
minutes
-Capacitance differences sub-1pF
Graphs from Dr. Michael Schertzer “Automated detection of
particle concentration and chemical reactions in EWOD
devices”
Phase Three: Design and Testing
Input Board: PCB Layout
Phase Three: Design and Testing
Input Board: Experimental Output
-Input Board was tested using the
designed circuit and outputted the
following waveform before fullwave rectification
-This demonstrates that the signal
is voltage-varying and can
demonstrate changes in magnitude
-Phase detection remains untested,
however the preliminary circuit
was promising
Phase Three: Design and Testing
Signal Generator: PCB Layout
Phase Three: Design and Testing
Signal Generator: PCB Layout
Phase Three: Design and Testing
Amplifier Functionality
-(+)9 V p-p from signal generator amplified to 120 V p-p
between ~100 - 100kHz
Phase Three: Design and Testing
Amplifier Functionality
-Simulated with a 600uH Resonant Converter Transformer
Phase Three: Design and Testing
Amplifier: Preliminary Design
-Breadboarded setup of amplifier design
Phase Three: Design and Testing
Amplifier: Preliminary Results
-Output waveforms at 10kHz and 100kHz
respectively
Phase Three: Design and Testing
Amplifier: PCB Layout
Phase Three: Design and Testing
Fault Detector: PCB Layout
Phase Three: Design and Testing
Indicator: PCB Layout
Phase Three: Design and Testing
Power Supplies
- Cosel +/- 15 V DC @ 1.7A
- Cosel +5 V DC @ 2A
Phase Three: Integration
Machining of
Enclosures
Phase Four: Final Design
Phase Four: Final Design
Phase Four: Final Design
Phase Four: Final Design
Performance vs. Requirements
Opportunities for Future Work
Housing
● 10 pin ribbon cable connector
● Protective paint coating
Input Board
● Purchase DropBot input board or modify existing software to work with
current board
Amplifier
● Modify design to use BNC connector instead of SMA
Power Supply
● Switch to using power supply from P15611