Two Arduino Nano Based AM PWM TX

860	D9 is 1600KHz carrier, Pin D6 is 64KHz Audio PWM. Audio sampling rate = 64KHz ADC operating at 1MHz Add 100n decoupling capacitor near pin 14 of 74H00 to prevent spikes.

const byte ANTENNA = 9;
int duty;
int raw;
int bias = 192;

void setup(){
// set up Timer 0
TCCR0B &= B11111000;
TCCR0B |= B00000001;
// PWM Boost pins 5 & 6 to 64KHz
// set up Timer 1
TCCR1A = _BV (COM1A0); // toggle OC1A on Compare Match
TCCR1B = _BV(WGM12) | _BV(CS10); // CTC, no prescaler
OCR1A = 4; // compare A register value to 10 (zero relative)


// ADC Boost Start - sets ADC clock to 1MHz
// defines for setting and clearing register bits
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

// set ADC prescaler to 16
sbi(ADCSRA,ADPS2) ;
cbi(ADCSRA,ADPS1) ;
cbi(ADCSRA,ADPS0) ;
// ADC Boost End
}
void loop(){
{
raw = analogRead (0);
duty = bias + ((raw - 512)/4);
analogWrite(6, duty);
}
}

Ivan, Arduino has 3 timer counters. I want to shrink the project to only only Arduino generating the two signals for CD4011.

Add a class D amplifier chain and it's super easy to get 10W of carrier. Transformer also gone. For the MOSFET drain matching use an air core .R1 x R2 x C1 x 0.455 = Frequency in Hz

R = Kilo ohm    
C = nF
R2 = R2 + VR1 

For VR1 use a 100K pot. R1 = 1Mcoil on PVC.  Mosfet driver and PA required.

Ivan wrote:A 4011 works with Vcc from 3 V up to 18 V. At lower Vcc it becomes a bit slower. If you feed it from 5 V, no level shifters are needed.

VBR Ivan

Oh. Would it work satisfactorily at 1600KHz with just 5V supply? I checked datasheet, at 10V it's 1/120nS or 8MHz max. Good idea! Thank you so much for correcting my mistake. 5V is good for CD4011 at 1.6MHz I just checked its datasheet.

A 4011 works with Vcc from 3 V up to 18 V. At lower Vcc it becomes a bit slower. If you feed it from 5 V, no level shifters are needed.

VBR Ivan

If we eliminate the 74HC00 then CD4011 can be used instead. CD4011 would work at 12V so a 5V to 12V level shifter with 2n7000 is needed to interface Arduino to nand gate mixer. Some extra parts but CD4011 is universally available even in local hobby shops or internet. CD4011 should work till 8MHz.

x/* Arduino Nano Audio PWM Modulator. Open for improvement. Changes to the code welcome.
Experimental 1.6MHz AM transmitter using PWM.

Audio Input on Analog 0, PWM output on Digital 6.
I/O circuitry as follows:
Input: capacitor couple iPhone audio through 10uF.
Bias Input pin to 2.5V with one 10k resistor to 5v,
and another 10k resistor to ground to form a voltage divider.

*/
int duty;
int raw;
int bias = 192;
void setup(){
TCCR0B &= B11111000;
TCCR0B |= B00000001;
// PWM Boost pins 5 & 6 to 64KHz

// ADC Boost Start - sets ADC clock to 1MHz
// defines for setting and clearing register bits
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

// set ADC prescaler to 16
sbi(ADCSRA,ADPS2) ;
cbi(ADCSRA,ADPS1) ;
cbi(ADCSRA,ADPS0) ;
// ADC Boost End
}
void loop(){
raw = analogRead (0);
duty = bias + ((raw - 512)/2);
analogWrite(6, duty);
}


SKETCH for carrier generator Arduino

const byte ANTENNA = 9;

void setup()
{
// set up Timer 1
TCCR1A = _BV (COM1A0); // toggle OC1A on Compare Match
TCCR1B = _BV(WGM12) | _BV(CS10); // CTC, no prescaler
OCR1A = 4; // compare A register value to 10 (zero relative)
} // end of setup

void loop() {}

Theory: The 16 MHz clock is divided by 5 (that is, 3.2MHz) and that is used to toggle pin 9 at that rate, giving a frequency of 1600 KHz, since one toggle turns the output on, and second toggle turns it off.

If you hold the Arduino near an AM radio tuned to around 1600 KHz you should hear a silent carrier.

The OCR1A variable is related to the frequency. The OCR1A variable is one less than the actual divisor. OCR1A - Frequency 15 - 500 khz 14 - ~530 khz 13 - ~570 khz 12 - ~610 khz 11 - ~670 khz 10 - ~730 khz 9 - 800 khz 8 - ~890 khz 7 - 1000 khz 6 - ~1140 khz 5 - ~1330 khz 4 - 1600 khz 3 - 2000 khz 2 - ~2670 khz 1 - 4000 khz 0 - 8000 khz *would not recommend this setting

The formula is (16÷(OCR1A+1)÷2)×1000 = frequency in khz.

Regarding the PWM generator, the Arduino emulates such chips as the SG3525 or TL494 without the complicated wiring needed to actually use one of these chips, as most of the work is done natively on the Arduino. Sampling rate is 64KHz which is quite good for 5KHz audio bandwidth of medium wave broadcast band. Changes are welcome to the code for any improvement. 6ft wire antenna with proper matching is recommended. Add a 3ft ground radial. It should comfortably cover a 3BHk house.




The OCR1A variable is related to the frequency. The OCR1A variable is one less than the actual divisor. OCR1A - 4 - 1600 khz (16/5/2)

The formula is (16÷(OCR1A+1)÷2)×1000 = frequency in khz
--------