In my schematic it's a simple 1n4148 diode.
The schematic is wrong, it's reversed.
So it limits the amp input to ~0.7V. All ok.
The ksger uses a LED to do the same thing.
6. hakko tip @ opamp o/p, while switching from 0% pwm to pwm on, you can see there is a significant drop in temperature, which of course over ramps the pwm and causes overshoot and hence vicious cycle.
The actual purpose of this project is to make a compatible firmware -with- existing soldering stations, just as they come from aliexpress, ande require the minimum modding from the user.
6. hakko tip @ opamp o/p, while switching from 0% pwm to pwm on, you can see there is a significant drop in temperature, which of course over ramps the pwm and causes overshoot and hence vicious cycle.
Does that statement corrrespond to this pic? I see it needs almost 4mS to be accurate! Now please repeat in lower voltage scale to see the variation in uV
If that is produced by the thermal impedance, we have a problem. We can't measure the temperature after each cycle on these, the wait is too long... 5mS is 25% of the pwm cycle!
I'll have to change back to tasked measurement, every x mS stop PWM, wait, measure, and resume PWM. I don't like that too much but if it works...
Or! We can apply a factor without waiting that much. Measure and removing a %. Although that may worsen the problem. I don't know.
Edit: I attach 0.1%, 0.5% , 1% and 2% min PWM bins. Please reset the settings holding the button before powering on (For now that settings are hardcoded and apply only on resetting). Please report results
And have a look at the temp! Anyway it's unlikely to burn the tip at 2%, I remember about 10% to hold the tip at 450ºC
This one is a chinese tip waking from sleep 0%, and it works perfectly.
I think you are right the inbuilt opamp diodes are sufficient.
Thanks for the bins I tried the 0.1% one but unfortunately it doesn't help, it seems the temperature reading error is proportionate to the duty cycle, i.e. 1% pwm, error is negligible but 50% pwm introduces a big error, temperature reads lower than actual. This means when the pwm is ramping down as we approach set point we have already overshot and nobody knows lol!
I don't like to admit defeat but I'm running out of ideas
Just for reference:
I just received a KSGER "2.1s" unit. It's what's called around here a "ve2.1s 'r2'". Except, it has a STM32F103RBT6 (128K flash). I'm guessing they buy the cheapest which are available when they do a run. #dreamcat4, you may want to note that on your page.
Pulled #DavidAlfa code from here. I think I've got it moved over to the B version (in addition to less flash, B doesn't have timers 6 & 8 ). Why does ST make this so hard??? Have an MCU on order to try (so I can unsolder the original as a backup), but it's not a B, I'll see how it works.
In any case, let me suggest that the STM32F103RBTx be used as the future target. AFAIK, that should be forward compatible with the C and higher versions. As David said:The actual purpose of this project is to make a compatible firmware -with- existing soldering stations, just as they come from aliexpress, ande require the minimum modding from the user.
Looking through github, I didn't see any obvious versions which support I2C displays, like the #DavidAlfa code mentioned above, including his git. Is the intent to eventually allow that to be #define'd into the mainline code?
Oh, don't be shy. Select the B part even if you have a "8". 99.99% It will work.
it's hardware i2c, these ksgers don't use it. A simple 2-wire mod will fix this, check this:
Can you post the exact picture where the TC goes lower with the PWM? I can't see a big difference in the TC output in your pics.
No, I have a "B", the archive is for a "C". "8" is nowhere to be found. But, I'll be replacing the B (which will be the backup) with an E, because that's what I can get soon. I don't doubt it will be fine. The point is that future builds should be for the "least common denominator", to support less sophisticated users in the future.
Edit: are all 103s the same die, and they just bin them when screening? There are so many, that doesn't provide much faith in their production processes.
If that was true, the TC would push negative voltage, the amp would always see ~0°C.
When the heater is on, the op-amp input is saturated and needs time to recover.
There are at least five different thermocouple op-amps out in the wild, and some are low power, slow parts. Their overload characteristics vary - some cheap op-amps phase-invert when overloaded, especially with any -ve input spikes.
Here are scope traces from my KSGER T12 H/W V2.1S with OPA336N op-amp "A36" and their D12 tip, idling at setpoint 300°C.
It shows the heater voltage along with TC op-amp output to give some clarity.
You can see the mosfet takes about 100usec to turn off.
The op-amp takes 250usec to desaturate.
The thermocouple-to-heater thermal time constant is about 1.7msec, so 5 tau to drop to 99.3% of settled value needs 8.5msec.
That gives us a blanking period of around 10msec required.
The PWM frequency is 5Hz (200msec). I think 50/60Hz worked for old triac controllers but we cannot use it due to the long (thermal) time constant of the TC. I don't see an advantage to usec timing, when the accuracy reading the TC is lost due to the high speed.