This is my very first microcontroller project; constructive criticism appreciated! Usable as is, but from here I will take a different tack, so I’ll post this as final before striking out in a new direction. Big picture, the object is to simulate output of a radiation detector, such as a Geiger-Muller tube or scintillator. This supports test and calibration on a longer-term counter/discriminator project.
I used a $4 Nano clone and junk box parts to build one, it works as intended. If I get a chance I’ll scan the schematic and append it. The method and performance are seriously torqued by limitations of the AVR chip; this post is evidently over length (9000 characters???), so I'll maybe add a comment later to discuss methods and constraints (if others are interested).
After a failed dalliance with an Arduino 101, I ordered a 32-bit 180 MHz Teensy 3.6 (with floating point unit) to play with. Well over 100x faster, makes this whole task completely trivial. Not looking back...
Thanks for reading!
Zike
/*
Random-interval pulse generator for testing radiation counter/scaler devices.
MEZ 14 April 2017
*/
#include <avr/pgmspace.h>
// store lookup table in progam flash
const unsigned int samples[] PROGMEM = {
827, 1037, 571, 165, 462, 716, 598, 737,
213, 204, 321, 341, 349, 665, 266, 246,
1395, 430, 800, 613, 1808, 114, 179, 333,
676, 38, 1374, 198, 492, 1351, 2186, 28,
971, 169, 641, 297, 274, 1372, 9, 174,
174, 1563, 272, 2382, 2651, 1418, 1969, 185,
// ...CONTINUES MANY PAGES...MAKE YOUR OWN...
26, 146, 432, 844, 3562, 2307, 348, 415,
206, 7, 414, 564, 484, 1043, 116, 152,
223, 243, 314, 682, 20, 512, 554, 69,
857, 323, 241, 116, 1016, 125, 950, 144
}; // 8192 values, mean = 599.26; MATLAB function exprnd(600,8192);
unsigned long adjustf = 16 ; // cal offset for execution time (fixed interval)
unsigned long adjust = 60 ; // cal offset for execution time (random interval)
unsigned long rseed = 3 ; // random number seed
unsigned long pulseWidth = 10 ; // microseconds
unsigned long tauMean = 600 ; // microseconds
unsigned long powerOffTime = 3600 * 1000L; // time to die (ms)
long multiplier = 1 ; //
long tau = tauMean; // negative values must be permitted
int buffySize = 1024;
byte fixedRate = 0; // mode
byte pulseOutPin = 7;
byte pulseBarOutPin = 6;
byte batteryCheckPin = 3; // resistive divider connected to Vin
byte controlRatePin = 1; // potentiometer wiper
byte ledPin = 11;
byte interruptPin = 2;
byte killSwitchPin = 9;
//------------------------------B76543210
byte outToggle = B00000000; // for setting bit mask
//unsigned long cum = 0; // diagnostics only
//unsigned long tic = 0; // diagnostics only
//unsigned long toc = 0; // diagnostics only
//unsigned long toe = 0; // diagnostics only
//unsigned long total = 0; // diagnostics only
//int b = 0; // diagnostics only
void setup() {
pinMode(killSwitchPin, OUTPUT);
digitalWrite(killSwitchPin, HIGH); // maintain board power after boot
pinMode(interruptPin, INPUT);
attachInterrupt(digitalPinToInterrupt(interruptPin), notAsimovThird, RISING); // next button press triggers kill
pinMode(ledPin, OUTPUT);
pinMode(pulseOutPin, OUTPUT);
pinMode(pulseBarOutPin, OUTPUT);
digitalWrite(ledPin, HIGH);
delay(100);
// digitalWrite(ledPin, LOW);
digitalWrite(pulseOutPin, LOW);
digitalWrite(pulseBarOutPin, HIGH);
buffySize = sizeof(samples) / 2; // 2 bytes per
rseed = rseed + (analogRead(A4)); // use open ADC noise to scramble PRNG seed (unnecessary, but free!)
// Serial.begin(115200);
// while (!Serial && millis() < 200);
// Serial.println("Random-Interval Pulse Generator v. 1.0.5"); Serial.println(" MEZ, 14 April 2017 ");
checkBattery();
multiplier = readPot(controlRatePin);
if (multiplier < 0) {
fixedRate = 1;
multiplier = -multiplier;
}
digitalWrite(ledPin, HIGH);
bitSet(outToggle, pulseOutPin); // output toggle mask set
bitSet(outToggle, pulseBarOutPin); // !output toggle mask set
// for (int k = 0 ; k < buffySize ; k++) { // check normalization of lookkup table
// total = total + pgm_read_word_near(samples + k);
// }
// Serial.println(); Serial.print("sample mean = "); Serial.println(total/buffySize);
// Serial.print("which should be close to "); Serial.println(tauMean);
//
// tic = micros();
} // end of setup()
void loop() {
if (millis() > powerOffTime) { // shut down to save battery
notAsimovThird();
}
if (fixedRate != 0) {
tau = (multiplier * tauMean - adjustf - pulseWidth);
}
else {
unsigned long j = (zrand() % buffySize); // pick a random index in [0, buffySize)
unsigned long value = (unsigned long) pgm_read_word_near(samples + j); // retrieve from prog flash
tau = (multiplier * value - adjust - pulseWidth);
}
tau = max(tau, 0); // avoid badness (floor)
holdOff(tau);
firePulse();
// diagnostics:
// toc = micros() - tic;
// if (b < 1000) {
// b++;
// cum = cum + toc ;
// }
// if (b == 1000) {
// Serial.println(cum);
// b = 0; cum = 0;
// }
// tic = micros();
} // end of loop()
/*
functions
*/
void holdOff(unsigned long bau) {
// delayMicroseconds() fails beyond 16383 us; split long delays into ms + remainder us
if (bau > 9999 ) {
delay(bau / 1000) ;
delayMicroseconds(bau % 1000 ) ;
}
else {
delayMicroseconds(bau);
}
} // end of holdOff
void firePulse() {
// digitalWrite() takes 5 us per bit; direct register xor < 1 us
// *** Atmega328 only *** change register name for other uP
PORTD = PORTD ^ outToggle ; // start pulse
delayMicroseconds(pulseWidth);
PORTD = PORTD ^ outToggle ; // stop pulse
} // end of firePulse
unsigned long zrand() {
// basic PRNG in style of C "rand()" function (Kernighan & Ritchie, 2nd ed., p.43)
rseed = rseed * 1103515245 + 12345;
return (unsigned long)(rseed / 65536) % 32768;
} // end of zrand()
void flashStatus(int nFlashes) {
// show parameters by blinking LED code
for (int k = 0 ; k < nFlashes ; k++) {
digitalWrite(ledPin, LOW);
delay(150);
digitalWrite(ledPin, HIGH);
delay(150);
}
delay(500);
} // end of flashStatus()
long readPot(int pin) {
// read potentiometer voltage, set parameter values, signal selections
int control = analogRead(pin) >> 7; // take only 3 MSB (0-7) (10-bit ADC boards only!)
switch (control) {
case 0:
{ flashStatus(1); flashStatus(2); return 1000; break; // 100 cpm (1.67 Hz) random
}
case 1:
{ flashStatus(1); flashStatus(3); return 100; break; // 1k cpm (16.7 Hz) random
}
case 2:
{ flashStatus(1); flashStatus(4); return 10; break; // 10k cpm (167 Hz) random
}
case 3:
{ flashStatus(1); flashStatus(5); return 1; break; // 100k cpm (1.67 kHz) random
}
case 4:
{ flashStatus(2); flashStatus(5); return -1; break; // 100k cpm (1.67 kHz) fixed
}
case 5:
{ flashStatus(2); flashStatus(4); return -10; break; // 10k cpm (167 Hz) fixed
}
case 6:
{ flashStatus(2); flashStatus(3); return -100; break; // 1k cpm (16.7 Hz) fixed
}
case 7:
{ flashStatus(2); flashStatus(2); return -1000; break; // 100 cpm (1.67 Hz) fixed
}
default :
{ flashStatus(7); return 1;
}
}
} // end of readPot()
void checkBattery() {
// ((7.5V-.25V)/5.0V ) * (100k/(348k+100k)) = 331/1023 ; .25V is schottky diode fwd drop
if (analogRead(batteryCheckPin) < 331) {
flashStatus(9);
}
} // end of checkBattery()
void notAsimovThird() {
digitalWrite(killSwitchPin, LOW); // goodbye cruel world
} // end of everything
