zelishmekhi
New Member
Step one: try to identify what's going on with the wires between the handset and transceiver.
Continue to Site
Yep, just with a coupling cap so the input pin has no external DC applied.
.
I was thinking for simplicity of prototyping / assembly - do those with three or more UARTs come in dual-in-line packages? Surface mount ICs make things and inconvenient complex, for prototyping..
Nice!
function calculateToneSamples(targetFreqs, sampleRate, sampleDataBits, terminator, maxErrorPct, maxCycles = 10) {
let totalSamples = 0;
const tones = targetFreqs.map((targetFreq) => {
const exactSamplesPerCycle = sampleRate / targetFreq;
let cycles = 0;
let intSamples, actualFreq, errorPct;
do {
++cycles;
intSamples = Math.round(exactSamplesPerCycle * cycles);
actualFreq = sampleRate * cycles / intSamples;
errorPct = (actualFreq - targetFreq) * 100 / targetFreq;
} while(Math.abs(errorPct) > maxErrorPct && cycles < maxCycles);
totalSamples += intSamples;
const data = [];
const halfAmplitude = ((1 << sampleDataBits) - 1) / 2;
for (i = 0; i < intSamples; ++i) {
let value = Math.round(halfAmplitude + halfAmplitude * (Math.sin(i * cycles * 2 * Math.PI / intSamples)));
if (value === terminator) {
++value;
}
data.push(value);
}
data.push(terminator);
return {
targetFreq,
actualFreq,
samples: intSamples,
cycles,
error: errorPct,
data
};
});
// Add one sample per tone for a terminator value.
// Multiple by 2 because each byte of data takes up a word of program memory
const totalBytes = (totalSamples + tones.length) * 2;
const csvReport = [
["Sample Rate", sampleRate].join("\t"),
["Max Error", `${maxErrorPct}%`].join("\t"),
["Target Hz", "Samples","Cycles", "Actual Hz", "Percent Error"].join("\t"),
...tones.map((tone) => [tone.targetFreq, tone.samples, tone.cycles, tone.actualFreq, `${tone.error}%`].join("\t")),
["Total Samples", totalSamples].join("\t"),
["Total Bytes", totalBytes].join("\t")
].join("\n");
console.log(csvReport);
return {
totalSamples,
totalBytes,
tones
};
}
Isn't that what I'm doing already? Or is there a different approach using a timer?
No, you're using a DAC - you can use PWM with a PIC timer to give decent quality audio, or for your application probably even simple squarewaves (followed by a crude filter).
www.pic24.ru
Why do you think you need balanced (differential) audio?.
Because that's what the phone handset is designed to work with: https://www.electro-tech-online.com...a-car-phone-from-the-90s.162764/#post-1415917
You're confusing yourself, the point of differential (balanced) inputs is so you can have the microphone 100's of feet away, presumably you're not doing this?. Simply strap it as unbalanced and feed it a single signal - if you're bothered about (or can actually notice) the small drop in level then simply increase the level a bit to compensate, or turn the gain up. Presumably you're attenuating the signal from the micro?, so just reduce the attenuation a little to compensate.Because that's what the phone handset is designed to work with: https://www.electro-tech-online.com...a-car-phone-from-the-90s.162764/#post-1415917
I have already determined that I can provide only a single audio signal and ground the second audio pin just to start testing things. It successfully produces sound, but of course that means the peak-peak voltage difference that the handset processes between the two signals is half of what it should be. This results in the sound volume being about 6dB lower than it should be.
If I want to produce sounds at full max volume, I'll eventually need to figure out how to generate an inverted "copy" of my audio signal. I really don't think I should just double the voltage of my signal to compensate for the absence of the inverted signal. It's tempting, but that might allow some smoke to escape or something
BTW - I successfully got some decently smooth filtered audio going from my MCU to the handset last night. Will post about that later.
