MSP430G2553 beacon

In a former post, I developed a simple beacon code to send my ham call sign KC9TUI to a flashing LED on the Texas Instrument Stellaris development board.  It's a great device - but it has a zillion tiny pins.  Tiny pins are not practical for the homebrewer.  So, I switched over to the MSP430G2553 (a much easier-to-solder 20-pin DIP), loaded the code, and moved it to breadboard.  I'm using an LM317 and some caps to select a voltage close to 3.3, and that powers the controller.  Notice the 10k resistor which connects pin 1 (Vcc power) to the RST pin 16.  This has to be in place or the controller doesn't do a thing.  Also, please forgive my, uh, somewhat over-rated caps.  I'll get something rated to 16V for the final circuits.  These were just the first caps I found.  Without them, the noise from the power supply chip can cause havoc with the MSP430.  I take that on faith, and have not yet experimented with noisy power sources.  The final project powered with batteries will be so quiet that I'm sure it's not an issue.

Here's a quick movie so you can see the LED flashing my call sign, KC9TUI.  How's your CW?

See the video on YouTube


The final design will be to draw a PNP emitter to ground.  That's a keying circuit I use which I learned in Experimental Methods in RF Design.  If you enjoy RF electronics then you just have to have it.  The filter design software that comes with it is easily worth the price.  I've built that "1st Transmitter" three different times.  It's just a great way to start experimenting with RF transmitters.

More on the beacon project when I get it planted inside a watertight project case.  The transmitter will run from rechargeables and a solar panel, so there's plenty more work to do before this all gets soldered and mounted.

MSP430 / Stellaris Beacon program

I like programming the Texas Instrument MSP430 and Stellaris micro-processors.  I have several of their kits, one of which is a Stellaris EK-LM4F120XL.  Obviously, you have to make sure you set your IDE to your chip type.  But I believe this will run OK on most MSP430 and Stellaris boards.  I imagine it would be easy to adapt to an Arduino or Raspberry Pi also.

I'm building a small 10mW transmitter with just the oscillator, first buffer, and the keying circuit as shown in "A First Transmitter", Experimental Methods in RF Design (EMRFD).  That circuit keys by grounding the base of a PNP transistor.  So I developed this to blink an LED, and will later adapt it to also ground an I/O pin.

Here's the code:

/*
  Beacon by John Burgoon KC9TUI  -  January 2016
  Blink an LED in Morse code using my callsign
  For the EMRFD 1st Transmitter, alternate the emitter pin of the keying transistor to ground instead of  (or, perhaps in addition to) flashing an LED.
  Hardware Required;
  * LaunchPad with an LED
This software is free for public use.  Please be certain to change the callsign to your own.
*/

// most launchpads have a red LED
#define LED RED_LED
#define DOTLENGTH 110 
#define EL_SPACE DOTLENGTH*1
#define CHAR_SPACE DOTLENGTH*3
#define WORD_SPACE DOTLENGTH*7
String CALL_MSG;

// the setup routine runs once when you press reset;
void setup() {                
  // initialize the digital pin as an output.
  pinMode(LED, OUTPUT);  
  CALL_MSG = String("BEACON");   // TWO_BY_TWO or BEACON, all else sends "73"
}

// the loop routine runs over and over again forever;
void loop() {
  if (CALL_MSG == "TWO_BY_TWO") {
      MORSE_C();MORSE_Q();delay(WORD_SPACE);
      MORSE_C();MORSE_Q();delay(WORD_SPACE);

      MORSE_D();MORSE_E();delay(WORD_SPACE);   
      MORSE_K();MORSE_C();MORSE_9();MORSE_T();MORSE_U();MORSE_I();delay(WORD_SPACE);
      MORSE_K();MORSE_C();MORSE_9();MORSE_T();MORSE_U();MORSE_I();delay(WORD_SPACE);

      MORSE_K();delay(WORD_SPACE);
  } else if (CALL_MSG == "BEACON") {
      MORSE_K();MORSE_C();MORSE_9();MORSE_T();MORSE_U();MORSE_I();delay(WORD_SPACE);TONE();delay(WORD_SPACE);

  } else {

      MORSE_73();delay(WORD_SPACE);

  }
}

void DASH() {
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(CHAR_SPACE);         // wait for a dash-length of time
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(EL_SPACE);           // wait for a dit-length of time
}

void DIT() {
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(EL_SPACE);           // wait for a dit-length of time
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(EL_SPACE);           // wait for a dit-length of time
}

void TONE() {
  digitalWrite(LED, HIGH);   
  delay(WORD_SPACE*2);         
  digitalWrite(LED, LOW);   
  delay(EL_SPACE);         
}

void MORSE_K() {
  DASH(); DIT(); DASH();delay(CHAR_SPACE);         
}

void MORSE_C() {
  DASH();DIT();DASH();DIT();delay(CHAR_SPACE);
}

void MORSE_9() {
  DASH();DASH();DASH();DASH();DIT();delay(CHAR_SPACE);
}

void MORSE_T() {
  DASH();delay(CHAR_SPACE);
}

void MORSE_U() {
  DIT();DIT();DASH();delay(CHAR_SPACE);
}

void MORSE_I() {
  DIT();DIT();delay(CHAR_SPACE);
}

void MORSE_Q() {
  DASH();DASH();DIT();DASH();delay(CHAR_SPACE);
}

void MORSE_D() {
  DASH();DIT();DIT();delay(CHAR_SPACE);
}

void MORSE_E() {
  DIT();delay(CHAR_SPACE);
}

void MORSE_73() {
  DASH();DASH();DIT();DIT();DIT();delay(EL_SPACE);DIT();DIT();DIT();DASH();DASH();delay(WORD_SPACE);
}
  

HW-8 IF transformer replacement

My cousin, Elmer, and lifelong pal KR3EP did some good old-fashioned horse-trading and, in the bargain, got his hands on a Heathkit HW-8.  He was kind enough to give it to me, so I started using it.  I instantly decided this was one of the perfect radios for me.  It's not too fancy, but it performs quite well.  It's one of the most-modified of radios, too, which means a lot is written about it.

This ad image was swiped from the web.  I'm old enough to recall the ad.

However, even though many people declare what they've done, very few show pics and explain the process.  So, when I realized that the 40m band had no signal at all, I decided to repair it and post the progress here.

This radio has excellent documentation online.  Google it up.  After some initial testing, I found that the 15.895 MHz crystal was getting the right voltage, yet was not oscillating.This crystal is mixed to produce the 7 - 7.250 MHz bandwidth when the "7 MHz" switch is pressed.  The diodes seemed OK, so I decided to follow the alignment procedure.  If you do this, OBTAIN THE CORRECT "twiddle" stick - a.k.a an "alignment tool".  You heard me.  USE THE RIGHT TOOL.  If one of your hands sneaks over and grabs a hex key, cut off that hand and put it, along with the hex key, in the trash.  DO NOT USE A METAL HEX KEY.  THIS MEANS YOU.

The little nylon hex adjustment tools are available to purchase on the Web, and if you want to fool with radios you really should have a set.  I purchased mine from eBay - the "Universal Color TV Alignment Tool Set - ST-13".  The seller shipped right away, so I had it in a jiffy. 

Some gomer in years past ignored this, and crushed the upper slug used to tune the 40m band.  It was stuck fast in the little cardboard tube and wouldn't budge.  So, I de-soldered it from the unit, along with its little metal shield.  The spot it came from is midway down the left edge.  There are actually six holes, since there are two for the lower slug wires and two for the upper slug wires and two for the shield.

The IF transformer is just a pair of wires on a cardboard form, with two adjustable ferrite slugs inside.

Also, you'll notice that I marked the "front" of the can and noted the way the slug-tuned inductor aligns with the board.  (The inductor has a mark also, hard to see).  It will save me having to figure it out from the schematic when I replace it.  If you look closely, you'll notice someone (probably the same person) slightly crushed the IF shield canister with a pair of pliers.  Doofus.  I'll call him "Ralph".  Don't be like Ralph.  If you want to use a hex key on a slug-tuned inductor or transformer, DON'T.  And if you crush the slug and decide to remove the shield from any old radio, de-solder the shield from the back side using a little solder braid.  DON'T CRUSH IT WITH PLIERS, IT WON'T COME OUT THAT WAY, RALPH.  Look closely at this picture, next to the hex nut mid-way down the right side of the frame, and you can see the hole where the IF transformer goes. 

The holes look burnt, but actually that's just old solder flux.  I'll clean it off later.

I contacted Earl Andrews up in Canada, who may be able to repair or maybe replace the transformer.  However, while I wait to see if I can restore the original part, I thought I'd experiment a little.  Calculations show that the lower inductor coil should measure somewhere in the range of 1.4 µH.  I measured this with my trusty LCR meter and found it to measure 1.390.  The lower slug was aligned to maximum voltage before I removed it, so that feels spot on.  The upper coil should be somewhere in the 0.771 µH range, but when I measured it I found 0.766.  So it's no wonder that the 40m crystal did not oscillate.

Thing is, we can go ahead and wind two inductors on toroid cores and solder them in just to see if we can get the radio working while we wait on the original inductor to be repaired.  So I'll do that and post the results here in a new entry.

LCR meter

The very first electronic measurement instrument I owned was a digital voltmeter.  Not long after that, I obtained a 15MHz oscilloscope.  But if I had it to do over again, I'd purchase a decent LCR meter.

I bought this Escitec VA520 at the 2015 Dayton Hamfest.  I have lost the business card of the gentleman who sold it to me; if I still had it, I'd send him a thank you note.  I can sit down to the bench and measure inductance with reasonable accuracy - something that is vital to understanding circuits.  One can often figure out a capacitance or a resistance, but to have a meter that gives me a quick, reasonably accurate L, and a Q at 1 - 100 kHz - well, that has added to my understanding of circuits by leaps and bounds.  I've never tried the USB connection yet, but when I sit down to characterize a batch of crystals for filtering I'll give it a whirl and report back here.

It's fairly simple to build one's own inductance meter, and I did so.  It's neat to build the circuit, test it against an industrial instrument, and realize one is within 2% of spec.  And lately I'm learning to program Nokia 5110s with MSP430 processors from Texas Instruments.  So I'll end up with a home brew L-meter with digital readout to sit next to this handsome VA250.

But here's the main point: if I had had a meter in my early days, I would have spent a LOT less time trying to figure out what I had in the scrap bin, and a LOT more time building things with what I had.

The most fun thing (next to measuring my way through an old cigar box full of RF chokes and Philco inductors from old radios) has been to wind a transformer on a core and then watch the measurement change as I adjust the wires.  It's fairly simple to rig up a known cap on a breadboard, attach the result, measure the resulting resonant frequency, and confirm the meter readings.  It's certainly good enough for the kind of hobby work I do.  Once I get that close, I can fine tune a toroidal inductor or transformer by moving the wires around.  But it's a real time-saver to measure before I solder, know I'm close, and fine tune later once everything else is in place.