1 using microcontrollers in amateur radio, an az el controller application a presentation for the...
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Using Microcontrollers in Amateur Radio, an AZ EL Controller Application
A Presentation For The Southwest Ohio Digital Symposium
Presented by Bill Erwin – N9CX January 10, 2009
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Things I Hope To Leave You With
Share my experience with the rotor controller project Explain why I made the choices I did How it works Status of the project
But more than that: Why a microcontroller was a good choice for this project What software development environments are all about Tempt you to consider experimenting with microcontrollers
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Feel free to ask questions at any time !
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Motivation For This Project
Developed an interest in LEO (Low Earth Orbit) satellites Led to an interest in a better antenna system Wanted to track LEOs with small beam antennas
Commercial rotors & controllers are available Didn’t want to commit that much money at this stage of interest
Decided to use inexpensive rotors & build my own controller
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Low Earth Orbit Satellites
Basically LEOs are orbital repeaters AMSAT has a lot of information on the WEB LEOs offer some special challenges
They move fast. Short contacts Low RF power
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LEO Satellites Vary In Both Size & Complexity
AO-51 (Echo) ~800 km orbit voice repeater PakSat BBS PSK31 Digital
SuitSat-1 (AO-54) Russian space suit Launched from ARISS ~355 km telemetry only temp & battery
N-Cube210x10x10 CMI LITER VOLUME(University Projects)
~690 km orbit
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Satellite QSOs Are Interesting!
There are a lot of “things” involved in working the LEO satellites! Computer screen Keyboard Mouse Downlink frequency Uplink frequency Doppler effects Code paddles or a microphone Azimuth of the satellite Elevation of the satellite
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So Many things – So Little Time!
The window for a QSO is often less than 8 minutes. If you can automate a few “things”, your QSOs may have
more “talk” time. This project is about automating the rotors for directional
azimuth & elevation antennas.
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My Approach To The Project
Research the WEB for similar projects Evaluate what I might do that is different Understand how rotors work Keep it (relatively) cheap Breadboard parts of the design to verify critical
assumptions
Rotor controller needs an LCD display & flashing LEDs!
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Why Use A Microcontroller Anyway?
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Choices To Make
Features Rotors Software Development tools & Environment Microcontroller
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Desirable Features
Work with the Nova tracking software Have 2 main modes: “manual” & “autotrack” Self-calibrate to any Pulser type rotor Remember antenna position during powerdown. Reliable beam positioning – within 5 degrees. Easy to update the controller software. Minimize cost
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The Rotor – You must understand the thing you are trying to control!
The Alliance U100
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Yes – You Can Stack Them
Azimuth
Elevation
The ability to put a pipe through the rotor body is fairly unique.
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Anatomy Of A U100 Rotor #2
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Anatomy Of A U100 Rotor #3
Physical stop tab
Pulser Cam
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Anatomy Of A U100 Rotor #4
Motor shaft Gear
Pulsing contact
Motor FrameMechanical Stop
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Commercial Controller for the U100 Rotor
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10 degree graduations on the dial
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The Original U100 Rotor Schematic Diagram
Rotor
Control Box
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Model of the U100 Rotor
+
-
360/ 0 Deg.
180
90270
2. tics/deg = tics/pulse / deg/pulse
1. deg/pulse = 360 Deg/# pulse (counted)
Strategy1. Do an initial calibration to detect
rotor’s pulse characteristics. 2. Absolute direction is known at each
pulse & at rotor physical stops.3. Time between pulses to estimate
position of rotor to a finer degree of resolution.
4. Time between pulses to detect rotor limit or problems.
Total feedback from the rotor
Note – A “tic” is 5 milliseconds
Calibration Mode calculates:
3. Use physical stops as a reference
physical stop
~ 100 MS// //
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Block Diagram Of the Rotor Controller
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Front Panel Switches
Front Panel LEDs
SS relays andPhasing capacitors15 vac
SS relaysPhasing capacitors15 vac
CW
CCW
Common AZ Rotor
Pulsing ContactOpto isolator
Pulsing ContactOpto isolator
down
up
Common EL Rotor
5 Volt regulatorMAX 232 chipCeramic resonatorEtc.
Support circuitry
Front Panel LCD
ATMEGA 16
Note - This diagram does not indicate pin assignments
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A FEW OF THE ATMEGA 16 FEATURES THE DATA SHEET IS 358 PAGES ! – 32 x 8 General Purpose Working Registers – Up to 16 MIPS Throughput at 16 MHz – 16K Bytes of In-System Self-programmable Flash program memory – 512 Bytes EEPROM – 1K Byte Internal SRAM – Two 8-bit Timer/Counters with Prescalers – One 16-bit Timer/Counter with Prescaler – Real Time Counter with Separate Oscillator – Four PWM Channels – 8-channel, 10-bit ADC – Byte-oriented Two-wire Serial Interface – Programmable Serial USART – Master/Slave SPI Interface – 32 Programmable I/O Lines YOU CAN NOT USE ALL AT SAME TIME – SHARE I/O PINS
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Microcontroller – Atmel Atmega16
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YOU GET A LOT OF FUNCTIONALITY IN A SINGLE PACKAGE
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Microcontroller – Save Time By Buying a Proto board
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I use this development board for almost allof my projects.
Saves a lot of soldering and cost about $17.00
I get it from “Spark Fun”.
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Partial Schematic of the Rotor Controller System – Rotor interfaces
30 VCT xfmr
Solid State Relays(opto isolated)
Micro Controller's power supply ( +5 vdc)
O
O1 2
X
(|<
<
VCC
~20 VDCCurrent source for LCD Backlight
O
O O
O
1 2
3 4
X|( )|
<
xO3 x
)|
U100rotor
To micro controller common
Rotor common
Current limit resistor
JGC-5F XJGC-5F
R3
AZ –CW PA0 (pin1) AZ –CCW PA0 (pin 2)
JGC-5F
15 VAC
15 VAC
X Front panel AZ Pulse LED\/\/\/
\
To I/O port pin
R1
AZ – PD6 (pin20)
X
3
O
O
O
O
XJGC-5F
AZ Rotor
110 VAC
\/\/\/\
R2
EL – PD7 (pin21)
To micro controller common
U100 EL Rotor
To I/O port pin
Front panel EL Pulse LED
1
4
2
X
4N25
4N25
470 2W
2K
2K
VCC
EL –UP PA2 (38)EL–DOWN PA3 (pin37)
|( )|
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Front Panel Switches – Interface to the Microcontroller Micro Controller Port assignments (Active low)
Port A Pin 0 - Azimuth ClockWise (CW) Port A Pin 1 - Azimuth Counter ClockWise (CCW) Port A Pin 2 - Elevation Up Port A Pin 3 - Elevation Down Port A Pin 4 - Calibrate momentary pushbutton Port A Pin 5 - Auto Track momentary pushbutton Port A Pin 6 - Azimuth Pulse input Port A Pin 7 - Elevation Pulse input
LCD Port assignments (4 bit data interface) Details are in a header file
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Development Environment
Rotor control cable
Debug data Serial port
Program flash memory using “avrdude” utility
Fedora Core 7 GNU/LINUXWith AVR-GCC tool chain
Windows – running NOVA
Novacomm1 protocol
Write/debug source code
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Features On My Rotor Control Box
2X16 BACKLIGHTED LCD
SPST
N.O. Pushbutton
N.O. Pushbutton
ON-OFF-ON
ON-OFF-ON
Indicates rotor pulse
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Manual Mode - AZ & EL Reading
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Auto track mode – tracking AO-10 satellite
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The Rotor Teststand
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A Look Under The Hood
Rotor power
Controller Board
Xfmr for controller board
Phasing caps/SS relay boards
Rotor wires plugIn here.
Programming header
Serial in from PCSerial out for debug
PWR cord connector
Fuse holder
Front Panel
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A Few Software Statistics
ATMEGA 16 Controller 16KBytes Flash (Program) memory 512 Bytes of EEPROM 1 K SRAM
Software Sizes Program 13394 Bytes Data 262 Bytes – Initialized read only data BSS 399 Bytes – initialized read/write data Total 13995 Bytes
30 source files All source is written in “C”
AVR-GCC Tool Chain programs
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High Level Software Design
BACKGROUND processing every 5 milliseconds Watch every switch in the system
Monitor & debounce every switch in the controller Advertise debounced state to the FOREGROUND processing
Maintain software timers Decrement every interrupt (5 ms)
FOREGROUND processing Manage a simple “state machine” based on operating modes:
Calibrate Initialize Manual Auto
Manages the front panel LCD display & LEDs Fault detection/recovery strategy
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Field Day 2008 Satellite Antenna Setup
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Performance Of The Controller
Used successfully in last two Field Days Sensitive to drag on the beams – coax
False detection of physical stop or obstruction Dressing the coax better resolved this Have changed “late pulse” detection parameters
Be sure the beams are oriented properly before raising the mast <Hi Hi>
I consider it a success but it has not seen extensive use
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Things Left Undone Need to get a better schematic in electronic form
Scattered around in a notebook now
Finish the front panel Print another front panel template and put plastic over it
Need to paint the box Understand other Pulser rotors better (AR-22)
Mainly for azimuth rotor use Motor power requirements may not be compatible
Adapt to “Potentiometer” type rotors - Perhaps Made some accommodations, but didn’t finish this
A few things in the software to clean-up
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Closing Thoughts About Antenna Rotors Pulsers have many issues to consider
Resolution - must interpolate Calibration process Must have persistent memory (power-down) for AZ & EL position Can find them reasonably priced at hamfests
Potentiometer type rotors seem less complicated Always know where the rotor is No persistent memory required for power-down No interpolation required No directional history needed Less opportunity to get out of sync. Nova tracking software may do most of the work for you But – these rotors may be expensive!
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FROM A SOFTWARE PERSPECTIVE
This was an interesting microcontroller project! Microcontrollers can be used for a lot of amateur radio projects! If you are patient and persistent you will be successful!
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