April 24, 2012

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Anatomy of a PICAXE SWR Meter
How to control things with a simple, inexpensive BASIC controller

Sure, you've heard of programming in BASIC before and maybe even heard of the PICAXE ... but have you actually ever tried it?!  It's lots easier than you think to whip up a simple controller for any number of useful circuits that we homebrewing hams find useful around the shack:  Morse keyers and keyboards, temperature displays, auto-voicing circuits, antenna rotator control, remote control in general, ... and perhaps even an SWR meter as we'll be discussing here.

73,
~George N2APB & Joe N2CX

Attendees ...

Audio Recording ... (Listen to MP3 recording)

Text Log from this week's session ...

<20:02:03>"George - N2APB": Everyone:  You can see the notes for tonight's session online at ... http://www.njqrp.org/teamspeak/Feb%2028.html
<20:18:45>"Joe - N2CX": Rookey link: http://midnightdesignsolutions.com/rookey/index.html
<20:21:22>"Carlos - PY1EGG": Folks, I must go now, Im sorry... Thanks, George and Joe!
<20:24:55>"Joe - N2CX": PSK Beacon link:
<20:24:57>"Joe - N2CX": http://www.njqrp.org/psk31beacon/psk31beacon.html
<20:25:47>"Gerry Jurrens N2GJ (laptop)": The notes for tonight's session are terrific!
<20:27:20>"Gerry Jurrens N2GJ (laptop)": Radio Shack is advertising that they sell the Arduino boards now!
<20:28:54>"Gerry Jurrens N2GJ (laptop)": http://blog.radioshack.com/tag/arduino/
<20:29:31>"Gerry Jurrens N2GJ (laptop)": http://www.radioshack.com/product/index.jsp?productId=12268262
<20:30:04>"Joe - N2CX": R/S also has some of the Parallax modlues such as IR detectors, Ultrasonic sensors, GPS RX, etc.
<20:31:41>"Gerry Jurrens N2GJ (laptop)": Joe, are those considered "Add-ons"?
<20:33:26>"Joe - N2CX": Wheen you type peter's address do not forget it is pHanderson.com.  If you type panderson.com you get something altogether different!
<20:38:35>"Rick K3IND": but u can add an external eprom for longer programs...
<20:38:58>"Nic - KF5ADE": Help What chart or web page? Please
<20:40:14>"Joe - N2CX": http://www.njqrp.org/teamspeak/Feb%2028.html
<20:41:54>"Nic - KF5ADE": Thank's!
<20:42:30>"Joe - N2CX": RFID yes!
<20:45:26>"Joe - N2CX": 14M2 PICAXE was not available when we designed the Growler, only the 14M.  Things get better all the time!
<20:46:28>"Rick K3IND": all the PICAXE manuals are online and therefor free.
<21:04:56>"Joe - N2CX": There is a table in the PICAXE docs to tell you the frequency of each number in the sound command
<21:08:17>"Joe - N2CX": SWR now 2:1
<21:12:55>"Nic - KF5ADE": So Many PIC so little time ;)
<21:13:35>"George - N2APB": See the Growler in action on YouTube ... http://www.youtube.com/watch?v=2JJ9o1GDrGM
<21:14:05>"George - N9DXP": Thanks so much Joe and George. Very good stuff!
<21:18:13>"Gerry Jurrens N2GJ (laptop)": RT Thanks so much Joe and George. Very good stuff!
<21:19:07>"Ray K2ULR": Mac client even has last week's comments!
<21:20:04>"Joe - N2CX": http://www.njqrp.org/teamspeak/Feb%2028.html
<21:27:37>"Chris - w0anm1": thanks guys! 73
<21:30:58>"Russ G3OTH": Thanks George and Joe for another excellent presentation, I hope to join up with you again next week.
<21:45:44>"Nic - KF5ADE": G- night 73's
<21:46:01>"Ray K2ULR": 73

 

PICAXE Capabilities Chart

 

 

 

The Growler

A low-cost, compact SWR bridge with LED bargraph display and varying audio tones to indicate measured results.  Morse code annunciation of specific SWR values.  Good up to 148 MHz.

The Growler is a descendant of the SWR bridge used in the Rainbow Tuner.  It keeps the multicolor LED bar graph display to give a visual SWR indication while adding audible outputs.  Its heart is a resistive bridge formed from surface mount power resistors.  Using surface mount devices and a compact layout provides operation through the 2 meter band as opposed to only HF coverage if leaded resistors were used as in the Rainbow Bridge.  The bridge resistors are sized to allow operation at full 5W QRP levels for periods of 15 seconds or less.  Simple diode detectors pick off forward and reverse RF and produce DC signals which are fed to PICAXE U1, analog to digital converter inputs.  The ratio of these is used to calculate SWR, which illuminates the LEDs.  A growling tone whose pitch is proportional to SWR is also controlled by U1 and sounded by the speaker.  When the RF signal ends, the speaker sends the SWR numerically in Morse Code.  Calculations based on the ratio of forward and reverse signals rather then their absolute numbers preserve measurement accuracy though the finite DC drop of the detector diodes results in increasingly optimistic SWR readings as RF power decreases below approximately one watt.

The Growler PCB

 

Growler Demo on YouTube

It's not perfect (was still being developed when the video was made), but you can see/hear the circuit in action! ... http://www.youtube.com/watch?v=2JJ9o1GDrGM

 

Parts List

PICAXE Editor

 

Growler Code

Section 1:  Header File Description

Section 2:  Declarations

Section 3:   Main Program

Section 4:  Morse Driver (subroutine)

 

 

References:

1) Introduction to the PICAXE System ... http://www.picaxe.com/docs/axe049.pdf

2) PICAXE-M2 Information ... http://www.picaxe.com/docs/picaxem2.pdf

3) Buying the PICAXE (plus useful reference material) ... http://www.picaxe.com/

4) Intro To The PICAXE Microcontroller ... http://picaxe.hobbizine.com/intro.html

5) Download the (free) programming Editor (for Windows) ... http://www.picaxe.com/Software/PICAXE/PICAXE-Programming-Editor

6) Gobs o' PICAXE links! ... http://elecurls.tripod.com/picaxe.htm

7) PICAXE Overview, by Peter Anderson ... http://www.phanderson.com/picaxe/picaxe_overview.html

 

 

 

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