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More Hardware
Real Time Embedded Systems
www.atomicrhubarb.com/embeddedLecture 8 – January 31, 2012
More Hardware
Section Topic
• Where in the books– Catsoulis chapter 4– Simon chapter 2,3
Operational Amplifier (OPAMP)
Noninverting Input
Inverting Input
OpAmp
The output is a function of the difference of the inputs.
If ( noninverting(+) > inverting(-) )Vout swings to +V
If ( inverting(-) > noninverting(+) )Vout swings to -V
Small changes of Vinresult in large changes of Vout
OpAmp
VinVin
Vin
Vout
V+
V‐
Vout
V+
V‐
non-inverting
inverting
OpAmp
Vout = Vin * Rf/Rin Output voltage is fed
back to inverting input.
Amplification (gain) can be controlled by varying Rf
Useful for amplifying weak signals
OpAmp
Vin
Vout
Vout= Vin��Rf / Rin�
What an OpAmp is
Comparator
A comparator is a type of OPAMP that is used for comparing 2 voltages.
Vref = reference voltage
Vin = voltage to be comparedNon-inverting
Inverting
Comparator
Vref
Vin
Vout
V+
Vout goes to V+ when Vin>Vref(non-inverting)
(non-inverting)
Comparator Application
When Vin exceeds Vref of voltage divider, Vout of opamp will go high and turn on LED.
It's a 1-bit analog-digital converter!
Schematics
How to read them Parts, symbols, wires, labels How to make them Other stuff
connection no connection
componentdesignation& value
ground
power supply
component
pin #
signal nameor symbol
schematicsignal name
Important Things
Crossing wire (but not connected)
Connecting wires
Vdd
Vss
Symbols
What does the “/” mean?
This /
RST means the same as /RST
What does the “/” mean?
This /
RST means the same as /RST
/ Means “active low”
What does the “>” mean?
This >
What does the “>” mean?
That input is edge-triggered not level-triggered(positive edge-triggered in fact, rising edge)
This >
What does the “o” mean?
What does the “o” mean?
o = invert (active low) All others assumed active high
So what would “o>” mean?
Like this
So what would “o>” mean?
Like this
o = invert the edge trigger Edge-triggered on the FALLING edge.
Buses
A grouping of common signals. For examplem a Data Bus will contains
all 8 or 16 bit data lines (D0..D7 or D0..D15).
How to make schematics
Lots of free/low cost tools editors www.expresspcb.com www.pcb123.com
ExpressPCB
ASCII Art Schematic
+5 ---+---------------+---+| | |R +----------+|(see below) | 8 4 |
+---+------+-----|7 3|------/\/\/\---+------- Vout| | | LMC555 | |C to test +-----|6 | -----| | | -----
ground +-----|2 5|----+ || | 1 | | ground| +----------+ 0.1 uF| | |
Clock ----+ ground ground^
(Use a fixed-width font )
GPIO
General Purpose Input/Output Connections through which the
microcontroller can connect to external peripherals.
Over Simplified IO pin
V+1 0 1 0 1 0 1 0
External pin
Input Register
1 0 1 0 1 0 1 0
Output Register
InputOutput
Register
A small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values.
What really happens when we push a button?
Using IO
BouncePush
Release
Approximately 20-200 ms of noise as the mechanical contacts bounce
Software solution
Wait 200 ms from first event
Another
1 0 1 0 1 1 1 0 0 0 0 0
Sample until n values are the same
SW1 on LAB board
An actual button
Hardware Solution
Many solutions, this is a simple one
Hardware Debounce
Press button, discharge capacitor, release button to charge it.
Unfiltered button
Debounced button
Logic input Valid High
Hardware Solution
Debouce
Software? Hardware? Which is better?
LCD display
LCD (more)
Look at a Digital Compass
Look at a radio
LED Matrix
Remember basic schematic symbols,
labels, wires.
