HF Beacon, design questions

[syfr]

Nice work! I like island construction too. It goes fast ...

[greator]

I got a bunch of these SMI-05VDC-SL-2C relays, i havent worked with relays before, but i guess that a pulse between the two legs on the left(with the square) till make the contacts on the right to shift. Will the next pulse shift the other way, or do i need to revser the voltage to get it back to the first position?

[greator]

I did some tests with the relay, its not bi-stable/latching as i thought i was (Latching relays seem to be hard to find). It does however have both NO and NC outputs, and draws 108mA when pulled. This might still be usefull, the NC contact could be used as a charge controller. If the solarpanel is connected to the NC pins on the relay, the relay could use 108mA to keep the panel disconnected from the battery when the voltage is too high(>14,5v or something). Power will be abundant when the sun is shining directly at the panel and the battery is fully charged.

The NC option would also be "safe" in the way that if the program in the Arduino stalls, the solar panel will be reconnected when the battery voltage is too low for the arduino to keep it disconnected, the circuit will be rebooted and start with the panel connected.

[Stretchyman]

Not sure why you've decided upon using a relay?

Why not use a MOSFET?

Turns on with uA!

Str.

[syfr]

Yeah, FET's are cheap and efficient.  I wasn't sure what you were going to do with the relays (they're handy to have around) but without latch function, they're power hungry.

How much current are you switching?

[greator]

Mosfet sounds like a good idea, i wish i had read your posts before i epoxyglued two relays to the board 

I need the relay function for two things, regulating the solar panel and powering on the transmitter. The current from the solar panel will be something lika 1.2-1.5A, the transmitter will be lower.

I have a couple of IRF510 mosfets, i havent much experience working with them but i guess they would work as low-side relays in the way the image shows.

[greator]

Today i did some debugging of the program code, and tested it using different voltages. I recently got an oscilloscope, i thought i would try it out and it was a easy way to visualise the output from the transmitter.  The code is "BMX1 1101 1110". Im new to oscilloscopes, but thought i might try using this to build the qrp transmitter my self in stead of using the one i ordered online.

The epoxyglue did come of pretty easy, soon there will be a couple of Mosfets instead. I read up on how they work, and there will probably be one IRF510 in inverted mode(to disconnect the solar panel) and one that is non-inverted keying the transmitter and turning it on.

[QRP]

Dave Richards (AA7EE) has written an interesting article detailing his 1mW solar-powered HiFER beacon project

https://aa7ee.wordpress.com/2019/01/03/putting-the-hifer-brs-boris-beacon-on-the-air-finally/

https://aa7ee.wordpress.com/2018/05/07/the-boris-beacon-a-1mw-solar-powered-hifer-beacon/

[greator]

Nice project AA7EE did, very goog looking circuits!

I did some more experimenting with the IRF510 as a switch, and managed to use it to stop charging the battery from my adjustable PSU, but for some reason it didnt manage to cut the power from the solar panel. Instead of getting into this problem i decided to keep it simple, im using a 6W solar panel that wont be able to overcharge the battery to much, so no charge controller will be needed.

I made the board a bit smaller to fit into a nice box i found, too keep the hole package weather protected. As the circuit is now there is two inputs(voltage and temperature) and two outputs, keying transmitter and powering on the transmitter(probably with a Mosfet).

Im happy with the code, so there will probably dont be much changes to it now. I will start with the transmitter instead.

[syfr]

Really nice work. And it works which is even better!

Congrats. That's a really nice looking transmitter .   When Im debugging/building something new it usually ends up looking like a dogs breakfast.   You did a nice job

[greator]

Today i got started on the transmitter part, the oscilator has been built using the octal buffer 74HCT240(there are lots of designs with this IC online). The PCB is still a bit ugly with a 56ohm dummy load attached, but it works fine! I tested it out with a 8MHz xtal i had on hand.

The oscillator draws 16mA on idle and 69mA on operation. It puts about 45mW into a dummyantenna. Next step is to tidy up the circuitboard(the 7808 is a bit oversiezed etc..). Then it will need an amplifier to get it up to some more TX-power, and a low pass filter to get rid of the harmonics.

The digital oscilloscope is really handy, i was a bit hesitant before i bought it but for what im using it for it works really well.

[greator]

The circuit is now put inside a IP67 plastic box, togheter with the oscillator, the amplifier and a lowpass filter. The amplifier(IRF530) puts out about 2 watts of RF power after the lowpass filter(1,4-2,8 depending on the battery voltage). The current draw during transmitt is 482mA, and 16mA during idle.

Next step is to connect the keyer and the "power upp" Mosfet between the Arduino and the transmitter.

[syfr]

That's looking really nice, and I'll look forward to listening for it.

that output filter sure neatened up that waveform!

[greator]

I got a BUZ11 mosfet to work as a switch that powers down the transmitter between transmissions. The circuit is now installed in my garden, using a dummy load, to test it out for bugs and design flaws.

I tried out a few different crystals between 4 and 8 MHz, but didnt get it to work with any other than the 8MHz. The oscillator seams to work with them all, but the power amplifier doesnt, output is either highly distorted or lacking RF-power. With the 7,023MHz output grew with time, staring at 0,2W ending at 0,5W after 30s. Its all pretty strange, i will have to look into it some more.

Power consumption is down to 10mA on idle, with the 5aH battery it should be able to stay alive during dark winter months(even if its not transmitting).

Code: [Select]

#include <LowPower.h>

int len = 80; //set speed to 15 wpm
int sleeps = 0;
void setup()
{
  Serial.begin(9600);
  pinMode(13, OUTPUT);

}

//
void loop()
  {
  int voltage = analogRead(A7); //init voltage ADC
  //Serial.println(voltage);
 
  if ((voltage > 382) && (sleeps > 16)) //if voltage is below 11v hybernate
     {
      Serial.println("sending beacon");
      sendbeacon();
      sleeps = 0;
      }   
  else
      {
      LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF); 
      sleeps++;
      }
   
 
 
  }

int dot()
  {
  digitalWrite(8, HIGH); //send short beep
  delay(len);
  digitalWrite(8, LOW); //send short beep
  delay(len);
  }

int dash()
  {
  digitalWrite(8, HIGH); //send short beep
  delay(len*3);
  digitalWrite(8, LOW); //send short beep
  delay(len);
  }
 
int sendbeacon()
  {
  digitalWrite(10, HIGH); //power on transmitter
  int beeps = 0;
  dash();
  dot();
  dot();
  dot();
  delay(len*3);
 
  dash();
  dash();
  delay(len*3);

  dash();
  dot();
  dot();
  dash();
  delay(len*7);

  dot();
  dash();
  dash();
  dash();
  dash();
  delay(len*7);
 
  int voltage = analogRead(A7); //init voltage ADC
  int myNum = (voltage - 288)/16; // 8v = 0000, 15v = 1111
  int zeros = String(myNum,BIN).length();
 
 //below is convertion to binary string from decimal integer for voltage
  String myStr;
    for (int i=0; i<zeros; i++)
      {
      myStr = myStr + "0";
      }
  myStr = myStr + String(myNum,BIN);   
   Serial.println(myStr);       
                   
  for(int i=4;i<8;i++)
      {
      if(myStr[i] == '1')
        {
       
        digitalWrite(8, HIGH); //send long beep = 1
        delay(len*3);
        digitalWrite(8, LOW);
        delay(len);
        }
      else
        {
       
        digitalWrite(8, HIGH); //send short beep = 0
        delay(len);
        digitalWrite(8, LOW);
        delay(len);
        }
       
      delay(len*3);
      }
delay(len*7);
//Send temperature

int temp = analogRead(A6); //init voltage ADC

  myNum = 17 - (temp - 124); // 0 = -10 and 16 = +30
  zeros = String(myNum,BIN).length();
 //below is convertion to binary string from decimal integer
 
 
    for (int i=0; i<zeros; i++)
      {
      myStr = myStr + "0";
      }
  myStr = String(myNum,BIN);         
  Serial.println(myStr);           
  for(int i=0;i<4;i++)
      {
      if(myStr[i] == '1')
        {
        digitalWrite(8, HIGH); //send long beep = 1
        delay(len*3);
        digitalWrite(8, LOW);
        delay(len);
        }
      else
        {
        digitalWrite(8, HIGH); //send short beep = 0
        delay(len);
        digitalWrite(8, LOW);
        delay(len);
        }
       
      delay(len*3);
      }
  digitalWrite(10, LOW); //power off transmitter

   
 
  }

[syfr]

You transmitting into a 50 ohm load at both 4 and 8 Mhz?