I actually have a proof of concept circuit working. As I said earlier, I scrapped entirely the idea of floating the ground reference negative.
I also realized that I don’t need anything external to create two anti-phase LFO signals, the Arduino is capable of that on it’s own. I still want to go with the dual LFO setup for a reason. I want the bias voltage that I feed the output tubes to swing both up and down from it’s “off” position, not swing just up or down from where it is at rest. That way when the tremolo is switched on or off there is no perceived increase or decrease in overall volume.
Couldn’t the depth of the effect be controlled in software? Isn’t the point of using an Arduino that you could do things like that without additional hardware?
That’s a good point, but I’m not sure exactly how I would achieve it right now. Square wave would be no problem, and sawtooth I think I could figure out. But the sine wave is being generated via a lookup table. I’m not that great with C++. I’ll go ahead and attach the code I’ve got.
/*
* Controlled startup eliminates 'Standby' switch
* Control two banks of vactrols for channel switching
* Initialize lfo for tremolo and select waveform
*
* Written 03/2020 by Nathan Fisher <nfisher.sr@gmail.com>
*
* mains relay circuit on pin 12
* channel switches pin 2 between 5v and ground
* channel 1 output (relay or vactrol) pin 3
* channel 2 output (relay or vactrol) pin 4
* LFO A on pin 5
* LFO B on pin 6
* trem on/off switches pin 7 between 5v and ground
* tremolo indicator led on pin 9
*/
// setup the pins for various purposes
// connect our mains relay circuit to pin 2
const int mainsRelayPin = 12;
// channel switching
const int chswitchPin = 2; // channel switch spst switch on/off
const int ch1Pin = 3; // first bank of vactrols
const int ch2Pin = 4; // second bank of vactrols
int chswitchState = 0; // variable reading channel switch state
// tremolo section
int trswitchState = 0;
int trmode = 0;
const int traPin = 5; // pwm wave here
const int trbPin = 6;
const int trswitchPin = 7; // tremolo on/off switch
const int trindPin = 9;
// sine wave positions
byte sina = 0;
byte sinb = 0;
// the value for each position in the sine and sine reverse tables
byte s = 0;
byte r = 127;
// the tremolo rate
int interval = 10;
// counts the intervals that have passed, increments each time
int loopCount = 0;
// decrements each interval
int looprevCount = 255;
// store last update time
unsigned long previousMicros = 0;
// Our sine wave table for trem
const byte sineTable[] = {
128, 131, 134, 137, 140, 143, 146, 149, 152, 155, 158, 162, 165, 167,
170, 173, 176, 179, 182, 185, 188, 190, 193, 196, 198, 201, 203, 206,
208, 211, 213, 215, 218, 220, 222, 224, 226, 228, 230, 232, 234, 235,
237, 238, 240, 241, 243, 244, 245, 246, 248, 249, 250, 250, 251, 252,
253, 253, 254, 254, 254, 255, 255, 255, 255, 255, 255, 255, 254, 254,
254, 253, 253, 252, 251, 250, 250, 249, 248, 246, 245, 244, 243, 241,
240, 238, 237, 235, 234, 232, 230, 228, 226, 224, 222, 220, 218, 215,
213, 211, 208, 206, 203, 201, 198, 196, 193, 190, 188, 185, 182, 179,
176, 173, 170, 167, 165, 162, 158, 155, 152, 149, 146, 143, 140, 137,
134, 131, 128, 124, 121, 118, 115, 112, 109, 106, 103, 100, 97, 93, 90,
88, 85, 82, 79, 76, 73, 70, 67, 65, 62, 59, 57, 54, 52, 49, 47, 44, 42,
40, 37, 35, 33, 31, 29, 27, 25, 23, 21, 20, 18, 17, 15, 14, 12, 11, 10,
9, 7, 6, 5, 5, 4, 3, 2, 2, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 2,
3, 4, 5, 5, 6, 7, 9, 10, 11, 12, 14, 15, 17, 18, 20, 21, 23, 25, 27, 29,
31, 33, 35, 37, 40, 42, 44, 47, 49, 52, 54, 57, 59, 62, 65, 67, 70, 73,
76, 79, 82, 85, 88, 90, 93, 97, 100, 103, 106, 109, 112, 115, 118, 121,
124
};
// the setup function runs once when you press reset or power the board
void setup() {
// initialize digital pin mainsRelayPin as an output.
pinMode(mainsRelayPin, OUTPUT);
// wait for the valves to warm up
delay(15000);
// switch the relay on
digitalWrite(mainsRelayPin, HIGH);
// initialize the vactrol pins as outputs
pinMode(ch1Pin, OUTPUT);
pinMode(ch2Pin, OUTPUT);
pinMode(trindPin, OUTPUT);
// initialize tremolo pins as output for square wave use
pinMode(traPin, OUTPUT);
pinMode(trbPin, OUTPUT);
}
// the program
void loop() {
// get the channel switch state
chswitchState = digitalRead(chswitchPin);
// switch banks of vactrols on/off for channel switching
if (chswitchState == HIGH) {
digitalWrite(ch1Pin, HIGH);
digitalWrite(ch2Pin, LOW);
} else {
digitalWrite(ch1Pin, LOW);
digitalWrite(ch2Pin, HIGH);
}
unsigned long currentMicros = micros();
// switch the tremolo on/off
trswitchState = digitalRead(trswitchPin);
if (trswitchState == HIGH) {
interval = (analogRead(1) * 20 + 1);
if (currentMicros - previousMicros >= interval) {
// save the last pwm state change time
previousMicros = currentMicros;
// reset loopCount and looprevCount at the end of cycle
if (loopCount >= 255) {
loopCount = 0;
}
if (looprevCount <= 0) {
looprevCount = 255;
}
// increment through the sine wave tables
s++;
r++;
// increment the loop count, for square and saw waves
loopCount++;
// decrement the looprev count for sawrev wave
looprevCount--;
}
trmode = (analogRead(2)); // read our tremolo mode switch
if (trmode < 300) {
sina = sineTable[s];
sinb = sineTable[r];
analogWrite(traPin, sina);
analogWrite(trbPin, sinb);
analogWrite(trindPin, sinb);
} else if (trmode < 600) {
analogWrite(traPin, loopCount);
analogWrite(trbPin, looprevCount);
analogWrite(trindPin, looprevCount);
} else if (trmode < 900) {
analogWrite(traPin, looprevCount);
analogWrite(trbPin, loopCount);
analogWrite(trindPin, loopCount);
} else {
if (loopCount <= 127) {
digitalWrite(traPin, HIGH);
digitalWrite(trbPin, LOW);
digitalWrite(trindPin, LOW);
} else {
digitalWrite(traPin, LOW);
digitalWrite(trbPin, HIGH);
digitalWrite(trindPin, HIGH);
}
}
} else {
digitalWrite(trindPin, LOW);
// set the LFO pins to mid level
analogWrite(traPin, 127);
analogWrite(trbPin, 127);
}
}
I’m sure there are more elegant ways to achieve what I’m doing, but for the moment I’m pretty happy that it’s doing what I want it to.
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