@@ -80,28 +80,29 @@ int main(void)
// Startup screen
ssd1306_DrawString("therm v0.1", 1, 40);
ssd1306_DrawString("protofusion.org/therm", 3, 0);
delay(1500);
ssd1306_clearscreen();
GPIO_ResetBits(LED_STAT);
// Main loop
while(1)
{
// Process sensor inputs
process();
// Run state machine
machine();
}
// Read temperature and update global temp vars
int16_t temp = 0;
uint8_t temp_frac = 0;
void update_temp() {
// Assert CS
GPIO_ResetBits(MAX_CS);
delay(1);
// This may not clock at all... might need to send 16 bits first
@@ -136,20 +137,75 @@ void update_temp() {
// Deassert CS
GPIO_SetBits(MAX_CS);
// PID implementation
int16_t last_pid_temp = 0;
uint8_t last_pid_temp_frac = 0;
int16_t i_state = 0;
#define WINDUP_GUARD_GAIN 100
int16_t update_pid(uint16_t k_p, uint16_t k_i, uint16_t k_d, int16_t temp, uint8_t temp_frac, int16_t setpoint)
// Calculate instantaneous error
int16_t error = (int16_t)setpoint - (int16_t)temp; // TODO: Use fixed point fraction
// Proportional component
int16_t p_term = k_p * error;
// Error accumulator (integrator)
i_state += error;
// to prevent the iTerm getting huge despite lots of
// error, we use a "windup guard"
// (this happens when the machine is first turned on and
// it cant help be cold despite its best efforts)
// not necessary, but this makes windup guard values
// relative to the current iGain
int16_t windup_guard = WINDUP_GUARD_GAIN / k_i;
// Calculate integral term with windup guard
if (i_state > windup_guard)
i_state = windup_guard;
else if (i_state < -windup_guard)
i_state = -windup_guard;
int16_t i_term = k_i * i_state;
// Calculate differential term (slope since last iteration)
int16_t d_term = (k_d * (temp - last_pid_temp));
// Save temperature for next iteration
last_pid_temp = temp;
last_pid_temp_frac = temp_frac;
int16_t result = p_term + i_term - d_term;
// Put out tenths of percent, 0-1000.
if(result > 1000)
result = 1000;
else if(result < -1000)
result = -1000;
// Return feedback
return result;
uint32_t ticks = 0;
uint32_t last_ssr_on = 0;
uint32_t last_led = 0;
int32_t setpoint = 0;
uint16_t k_p = 1;
uint16_t k_i = 1;
uint16_t k_d = 1;
uint8_t ssr_output = 0; // Duty cycle of ssr, 0 to SSR_PERIOD
int16_t ssr_output = 0; // Duty cycle of ssr, 0 to SSR_PERIOD
// Process things
void process()
update_temp(); // Read MAX31855
@@ -160,17 +216,32 @@ void process()
GPIO_ToggleBits(LED_POWER);
last_led = ticks;
// Every 200ms, set the SSR on unless output is 0
if((ticks - last_ssr_on > SSR_PERIOD) && ssr_output > 0)
if((ticks - last_ssr_on > SSR_PERIOD))
// Get ssr output for next time
int16_t power_percent = update_pid(k_p, k_i, k_d, temp, temp_frac, setpoint);
//power-percent is 0-1000
ssr_output = power_percent; //(((uint32_t)SSR_PERIOD * (uint32_t)10 * (uint32_t)100) * power_percent) / (uint32_t)1000000;
// Only support heating (ssr_output > 0) right now
if(ssr_output > 0) {
char tempstr[6];
itoa(ssr_output, tempstr);
ssd1306_DrawString("#=", 2, 45);
ssd1306_DrawString(" ", 2, 57);
ssd1306_DrawString(tempstr, 2, 57);
GPIO_SetBits(LED_STAT);
last_ssr_on = ticks;
// Kill SSR after elapsed period less than SSR_PERIOD
if(ticks - last_ssr_on > ssr_output)
Status change: