Those Little Black Chips
ME456: Mechatronics Systems Design
Chapter 9:
Electronic Building Blocks
Prof. Clark J. Radcliffe
Mechanical Engineering
Michigan State University
http://www.egr.msu.edu/classes/me456/radcliff
The Transistor (NPN)
•  A current amplifier …
–  Makes
small
currents BIGGER
•  Integrated Circuits (IC s)
–  Expand possible tasks for a microcontroller
–  Substitute hardware for software
–  This chapter includes
•  The Transistor (NPN)
•  The Digital Potentiometer
–  From one
to millions of transistors
–  Thousands in dedicated circuits
•  Amplifiers, LED drivers,
timers, clocks, …
–  Information on datasheets
Important 2N3904 Specifications
from the datasheet
Note high maximum ratings
•  The 2N3904 Transistor
β = 30-400
C= Collector
B = Base
E = Emitter
BUT 200mA maximum current
2N3904 Datasheet
Maximum Thermal Dissipation
•  Posted on the ME456 website
Depends on package BUT is always < 1 watt
Your package, max dissipation P = 0.65 W
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Electrical Characteristics
When the transistor is off
Electrical Characteristics
When the transistor is on
• Transistor will tolerate supply voltage on Collector
Δv > 40-60 volts
• Expect current leakage through collector
ileakage < 50 nA
Min Current Gain: 30 < β <100
Max Collector-Emitter Saturation Voltage: 0.3 volt
Note: Power dissipated, P=VI < 0.3volt*0.2A = 0.06 W
Gain: icollector = β*ibase
Text says β = 416 but that is a maximum…
Still… A powerful driver
100 mA load driven by 1 mA
AND load powered by unregulated supply
à Here, 10 mA is driven by 0.1 mA
Requiv =
R1 R2
RR
R
=
= = 50 k!
R1 + R2 R + R 2
Max ( ibase ) =
=
Vmax
Requiv
5 volt
50 k!
= 10 "4 Amp = 0.1mA
Potentiometer
produces voltages
0 < V < 5volt
β = 100 is more reasonable
Still… A powerful driver
100 mA load driven by 1 mA
AND load powered by unregulated supply
à Here, 10 mA is driven by 0.1 mA
Max ( icollector ) = Max ( ! " ibase )
Max ( ibase ) = 0.1mA
= 100 " 0.1mA
= 10 mA
Saving BS2 power…
•  With Transistor drive, you can use
the 9v battery instead of BS2 supply
–  Saves your limited 50 mA BS2 supply
•  Move Vdd connection to Vin
–  Now you are driving a 10 mA load
using unregulated power with
0.1 mA of regulated power!!!
•  How many LEDs can you drive
with a single BS2 pin?
NOTE: This IS NOT dependent on collector supply voltage
– use your 9v battery instead of BS2 supply!
–  Transistor Limit: 200mA/10mA => 20
–  BS2 limit: 20mA/0.1mA=>200
2
More Important I/O
Move LED connection from Vdd
-> to Vin
–  Save I/O pin power
Circuit will work the same
Now you are supercharged!
BE CAREFUL
This can’t be done with all circuits
(Careful analysis required)
The Digital Potentiometer
The Digital Potentiometer:
Acts the same as a standard potentiometer
Adjusts the wiper to change the resistance
to adjust the voltage at the wiper.
The Digital Potentiometer
The Digital Potentiometer
acts the same as a standard
potentiometer but is
controlled digitally.
The chip has
(3) potentiometer connections
(2) power connections &
(3) control connections
How it works
Each element = 78.125 ohms
128 *78.125 =10K ohm total.
With any single tap closed
10K ohm resistance is split
thus varying wiper voltage
The tap is digitally controlled
opens and closes 1 of 128
possible switches
(really transistors).
AD5220 Pin Summary
PIN
Purpose
1. CLK
Receives clock pulses to move the wiper terminal.
2. U
U/D
/D
A high signal moves the wiper (W1) towards A1, and a low
signal moves the wiper (W1) towards B1.
3. A1
The potentiometer s A terminal
4. GND
The ground connection. Vss on the BoE Board.
5. W1
The potentiometer s wiper (W) terminal.
6. B1
The potentiometer s B terminal.
7. CS
CS
The chip select pin. A low signal to this pin enables the chip.
8. Vdd
The Digital Potentiometer Circuit
Which Vdd could be Vin??? Why?
Connect to +5 V ( Vdd)
What do the bars over the symbols mean???
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Digital Potentiometer
Programming
A Variable Gain Amplifier
The wiper moved by setting direction and sending pulses
•  A Digital Potentiometer allows external
control of Op-Amp Gain
Set Direction
Low for Down to B1
RF
Pulse clock to move
tap 128 times
Reverse direction and repeat
RI
vI
vO
+
!
"R %
vO = ! $ F ' vI
# RI &
Helmholtz Resonator
for Noise Control
What can you use these for?
Semi-Active Resonator for Noise Control
•  The Helmholz Resonator acts at a single
frequency to absorb noise in a pipe
•  Semi-Active because the device is
actively tuned but uses no external energy
for the noise control itself.
–  Retuning makes it follow the noise frequency
–  Application: automotive exhaust noise
Semi-Active Helmholtz Resonator
for Noise Control
•  Resonance tuned to match incoming sound
frequency absorbs it all…
•  The perfect muffler if tuned precisely
•  The BS2 can tune it on line
Sound in
Sound
Absorbed
No
Sound
Out
BS2 Controlled Resonator
using Digital Potentiometers
•  Semi-Active Resonator: BS2 feedback
control tunes resonator precisely
even when the sound frequency changes
speaker
Sound in
Sound
Absorbed
BS2
Control
mic
No
Sound
Out
MSU SHR Video
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