Cons-n-Stuff/PCB-reflow-solder-heat-plate
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Added thermal approximation

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This commit is contained in:
Nathan 2022-04-22 20:26:36 -07:00
parent 8649afd315
commit bb03dec973
5 changed files with 9085 additions and 891 deletions
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115
Firmware/analysis/LMT85 study.ipynb Normal file
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186
Firmware/analysis/True Bed Temp Estimation.ipynb Normal file
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Firmware/analysis/data/thermal_analysis3.log Normal file
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Firmware/analysis/parser.ipynb
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Firmware/pcb_reflow_fw/pcb_reflow_fw.ino
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@ -74,7 +74,12 @@ byte max_temp_index = 0;
#define MAX_RESISTANCE 10.0
float bed_resistance = 0.9;
#define MAX_AMPERAGE 5.0
#define PWM_VOLTAGE_SCALAR 5.0
#define PWM_VOLTAGE_SCALAR 1.0
// These values were derived using a regression from real world data.
// See the jupyter notebooks for more detail
#define ANALOG_APPROXIMATION_SCALAR 1.752
#define ANALOG_APPROXIMATION_OFFSET -20.517
// EEPROM storage locations
#define CRC_ADDR 0
@ -84,8 +89,8 @@ float bed_resistance = 0.9;
#define DIGITAL_TEMP_ID_ADDR 10
// Voltage Measurement Info
float vConvert = 52.00;
float vMin = 10.50;
#define VOLTAGE_REFERENCE 1.5
// Solder Reflow Plate Logo
static const uint8_t PROGMEM logo[] = {
@ -664,6 +669,32 @@ bool heat(byte max_temp, int profile_index) {
}
}
void evaluate_heat() {
debugprintln("Starting thermal evaluation");
uint8_t duties[] = {255, 225, 200, 150, 100, 50, 0};
unsigned long runtime = 60*5; // run each for 5 minutes
for(int i = 0; i < sizeof(duties); i++) {
debugprint("Running to duty of: ");
debugprintln(duties[i]);
unsigned long start_time = millis();
analogWrite(MOSFET_PIN, duties[i]);
float elapsed_time = (millis() - start_time)/1000.0;
while(elapsed_time < runtime) {
debugprint("elapsed time: ");
debugprintln(elapsed_time);
debugprint("runtime: ");
debugprintln(runtime);
elapsed_time = (millis() - start_time)/1000.0;
float v = getVolts();
float t = getTemp();
delay(500);
}
}
analogWrite(MOSFET_PIN, MOSFET_PIN_OFF);
}
void stepPID(float target_temp, float current_temp, float last_temp, float dt, int min_pwm) {
float error = target_temp - current_temp;
float D = (current_temp - last_temp) / dt;
@ -832,26 +863,31 @@ float getTemp() {
t = t + analogRead(TEMP_PIN);
}
t /= 100.0; // average
t *= 1.5 / 1024.0; // voltage
t *= VOLTAGE_REFERENCE / 1024.0; // voltage
// conversion to temp, consult datasheet:
// https://www.ti.com/document-viewer/LMT85/datasheet/detailed-description#snis1681040
// this is optimized for 25C to 150C
// TODO(HEIDT) this is linearized and innacurate, could probably use the nonlinear
// functions without much overhead.
t = (t - 1.365) / ((.301 - 1.365) / (150.0 - 25.0)) + 20.0;
debugprint(t);
t = (t - 1.365) / ((.301 - 1.365) / (150.0 - 25.0)) + 25.0;
// The analog sensor is too far from the bed for an accurate reading
// this simple function estimates the true bed temperature based off the thermal
// gradient
float estimated_temp = t*ANALOG_APPROXIMATION_SCALAR + ANALOG_APPROXIMATION_OFFSET;
debugprint(estimated_temp);
debugprint(" ");
// return the maximum of all the temperature sensors for safety
sensors.requestTemperatures();
for (int i = 0; i < sensor_count; i++) {
float temp_in = sensors.getTempC(temp_addresses[i]);
debugprint(temp_in);
debugprint(" ");
t = max(t, temp_in);
}
debugprintln();
return t;
return max(t, estimated_temp);
}
float getVolts() {