MINTEMP  

RE: MINTEMP

I had the error then my thermister (hotend) had a short.  

RE: MINTEMP

a shorted thermistor normally causes a MaxTemp event

regards Joan

RE: MINTEMP

The thermistor is working fine. It just (correctly) reads a temperature low enough that the firmware complains. I'm asking which #define in the firmware adjusts the threshold, since it doesn't seem to be HEATER_0_MINTEMP.

RE: MINTEMP

Odd.  Is this the Mosquito thermister or Prusa?  

RE: MINTEMP

Posted by: holmes4

The thermistor is working fine. It just (correctly) reads a temperature low enough that the firmware complains. I'm asking which #define in the firmware adjusts the threshold, since it doesn't seem to be HEATER_0_MINTEMP.

I haven't looked deeply into this, but I'm also curious about how it all works. I once printed at 8°C ambient - and it worked. There is a HEATER_MINTEMP_DELAY to give the printer a bit of time to heat up before the checking starts. Once with the MMU I saw a Mintemp-Error after a finished print at 15°C ambient - (I still don't understand why).

Also in temperature.cpp there is this:

// Wait for temperature measurement to settle
_delay(250);

#ifdef HEATER_0_MINTEMP
  minttemp[0] = HEATER_0_MINTEMP;
  while(analog2temp(minttemp_raw[0], 0) < HEATER_0_MINTEMP) {
#if HEATER_0_RAW_LO_TEMP < HEATER_0_RAW_HI_TEMP
  minttemp_raw[0] += OVERSAMPLENR;
#else
  minttemp_raw[0] -= OVERSAMPLENR;
#endif

hj

So there is also a HEATER_0_RAW_LO_TEMP and a HEATER_0_RAW_HI_TEMP. It's also possible that this delay(250) here doesn't fit for every sensor.

Also there are 8 files where HEATER_0_MINTEMP is defined. The easiest error to fix would be to have picked the wrong one.

RE: MINTEMP

Posted by: charles.h13

Odd.  Is this the Mosquito thermister or Prusa?  

Crap, reading is fundamental.  I completely missed a whole sentence.  

RE: MINTEMP

Posted by: andreas.d10

Also there are 8 files where HEATER_0_MINTEMP is defined. The easiest error to fix would be to have picked the wrong one.

All of them are in the variants folder - you choose one of them to be Configuration_prusa.h. 

The code in temperature.cpp:

#ifdef HEATER_0_MINTEMP
  minttemp[0] = HEATER_0_MINTEMP;
  while(analog2temp(minttemp_raw[0], 0) < HEATER_0_MINTEMP) {
#if HEATER_0_RAW_LO_TEMP < HEATER_0_RAW_HI_TEMP
    minttemp_raw[0] += OVERSAMPLENR;
#else
    minttemp_raw[0] -= OVERSAMPLENR;
#endif

adjusts minttemp_raw from its initial value (16383 from thermistortables.h) until it is approximately what the ADC value corresponding to HEATER_0_MINTEMP is. OVERSAMPLENR is 16 (from thermistortables.h).

void check_min_temp_heater0()
{
//heater
#if HEATER_0_RAW_LO_TEMP > HEATER_0_RAW_HI_TEMP
if (current_temperature_raw[0] >= minttemp_raw[0]) {
#else
if (current_temperature_raw[0] <= minttemp_raw[0]) {
#endif
menu_set_serious_error(SERIOUS_ERR_MINTEMP_HEATER);
min_temp_error(0);
} else if( menu_is_serious_error(SERIOUS_ERR_MINTEMP_HEATER) ) {
// no recovery, just force the user to restart the printer
// which is a safer variant than just continuing printing
// The automaton also checks for hysteresis - the temperature must have reached a few degrees above the MINTEMP, before
// we shall signalize, that MINTEMP has been fixed
// Code notice: normally the alert_automaton instance would have been placed here 
// as static alert_automaton_mintemp alert_automaton_hotend, but
// due to stupid compiler that takes 16 more bytes.
alert_automaton_hotend.step(current_temperature[0], minttemp[0] + TEMP_HYSTERESIS);
}
}

I think I now have a clue as to what's going on. For the Slice thermistor, the "bottom" of the table looks like this:

{ 1015*OVERSAMPLENR , 20 },
{ 1018*OVERSAMPLENR , 10 },
{ 1020*OVERSAMPLENR , 0 } //safety

analog2temp does this:

 for (i=1; i<heater_ttbllen_map[e]; i++)
{
if (PGM_RD_W((*tt)[i][0]) > raw)
{
celsius = PGM_RD_W((*tt)[i-1][1]) + 
(raw - PGM_RD_W((*tt)[i-1][0])) * 
(float)(PGM_RD_W((*tt)[i][1]) - PGM_RD_W((*tt)[i-1][1])) /
(float)(PGM_RD_W((*tt)[i][0]) - PGM_RD_W((*tt)[i-1][0]));
break;
}
}

It is interpolating between two table entries to calculate the Celsius temperature. A possible issue is that for my table, the difference between 20 and 10 is small, and perhaps the interpolation is coming out wrong. (Nevertheless, the display says 16 but I get MINTEMP with the value set at 10?) I am going to play with this code and see if I can get to the bottom of it. I'm actually dubious of the table entries at the bottom, as I am getting readings a bit lower than the actual room temp at startup. Maybe I'll fiddle with the values until I get something that looks good. I won't fuss with the higher temp values, as I have no indication they are wrong.

RE: MINTEMP

I ended up tweaking the bottom entries in the thermistor table and now it reads close to the actual room temperature - and no more MINTEMP. 

RE: MINTEMP

Posted by: @holmes4

I ended up tweaking the bottom entries in the thermistor table and now it reads close to the actual room temperature - and no more MINTEMP. 

What changes did you actually make to the thermistor table??

RE: MINTEMP

I am going to switch my Mosquito printer to the Mosquito plus Bondtech to prevent the need to edit termistor tables.  

RE: MINTEMP

Posted by: @cwbullet

I am going to switch my Mosquito printer to the Mosquito plus Bondtech to prevent the need to edit termistor tables.  

I just finally upgraded my Prusa MK3S to the Bondtech and Mosquito Magnum (450C thermistor and 50W heater). I had to edit the firmware myself as the Bondtech firmware they sent me di not work. I am still getting mintemp errors at startup. I am still trying to fix that!!

RE: MINTEMP

I just talked to Greg at Slice Engineering and they are now selling PT1000 thermistors. He said he likes them better than the 450C thermistors they sell.

RE: MINTEMP

@gorillamotors

The firmware is posted on the website and updated to 3.93.  

RE: MINTEMP

@gorillamotors

I do not see them on their website.  

RE: MINTEMP

Posted by: @cwbullet

@gorillamotors

I do not see them on their website.  

Never mind, I found it.