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Youyue 858D+ some reverse engineering + custom firmware

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I'm writing a custom firmware for this device. More to come pretty soon. More info on my blog.

What works so far:

    reading the 2 buttons
    reading the wand sensor (reed contact)
    fan ON / OFF override
    crude heater control – just ON / OFF


    read the thermo-couple voltage from the OP-7
    implement a control loop for the temperature (most likely PID) + sensible calibration
    read the fan status signal (not quite sure what it is)

For now, here's a part of the schematic and a short video.

A bit of a quinky-dink....   

Check out the ** SCHEMATIC ** and  ** PROGRAM **
posted at

I just got through reverse engineering a YiHUA 937D Temperature controlled soldering iron.
It's a bit simpler then your 858D+, but you might find some of the work useful.

NOTE: Schematic done with KiCad (Open Source "Schematic and PCB designer" Dave reviewed some time ago)
NOTE: If you want the KiCad files, let me know.

george graves:
What's your goals in this?

Someone did a video, and apperently the display is totally faked, and that the air temp totally overshoots at start up.  Is that what you are trying to fix?

Also, think you can do it all with a firmware only solution - if so - that would be niceeeeeeeeeeeeeeeeeeeeeee!

The first goal is to get it to display the actual temperature and not just the set-point. The set-point is a nice-to know, but I really do like to know the real thing.

I've accomplished that. It is usable as of now.

The temperature overshoot issue is my 2nd goal. As of now I have implemented a PD control loop, which works reasonably well, but the parameters need more tweeking. Initial power-up is still a bit iffy with respect to overshoot, but once the device is warmed up, moving the temperature around isn't too bad. Work in progress :-)

I'll tweak the way the device controls the heater a bit more and may finally go to full PID control. Currently the very low temperatures ( < 130°C ) take too long to reach, as the minimum duty cycle for the heater is still too long, so the tiniest bit of heating action will almost overcompensate any intended temperature drop.

I hope there is a firmware-only fix for this device.

I think I'm done :-)

The massive overshoots are a thing of the past.

I've also managed to lower the minimum temperature to about 65°C and added the option to let it blow cold air.


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