Microcontroller projects

UYUE 946-1010: Convert a preheating station in a reflow solder station

last updated: 2024-03-22

Quick links

Introduction

In a video I saw, bitluni solder SMD components on a preheating station. I've tested an reflow oven (https://www.weigu.lu/other_projects/baking_smd/index.html), but for small pieces or to unsolder things I thought such a preheating station would be cool (or hot). When buying the sation I did not pay attention and bougt a 110 V station instead of a 220 V station. So I ordered a second station and will hack the first (or both) to get a reflow solder station :).

uyue 946 1010

Hacking

As Denis Bodor (Hackable Magazine) wrote, there is no better thing to do during a WE than hacking or reverse engeneering a device :).

So I have 2 UYUE 946-1010 preheating station. Both station are labeld with 400W. By opening the stations I found:

110 V Station:
3 heating elements (8 mmx60 mm) 110 V/100 W
R = 110 V²/100 W = 121 Ω, Rtotal = 40 Ω
Measured R = 40.3 Ω
Hotplate 10x10x 8.3mm³

uyue 946 1010 plate

220 V Station:
2 heating elements (8 mmx60 mm) 220 V/150 W
R = 220 V²/150 W = 323 Ω, Rtotal = 161 Ω
Measured R = 155 Ω
Hotplate 10x10x 6.1mm³

Both station have the same PCB! labeled YYUVDJS-220V V1.0.

I could use the 110 V station with 220 V and a max 25% PWM, but this is a little risky, so I ordered 3 heating elements 220 V/100 W

By looking at the components I found a BTA16-800B Triac with an EL3083 zero cross TRIAC driver to switch the heating elements. A chip labeled SZ2525C (7-Pin) is an AC/DC converter like an LNK304GN or similar. Here I couldn't find a datasheet, but the circuit shows that we produce a small DC voltage that is followed by an classical 78L05 to produce 5 V.

uyue 946 1010 pcb top      uyue 946 1010 pcb back

A 5 pin header (not soldered) is connected to the 20 pin microcontroller. The µC is not labeled but after a little research I think it is an STM8103F3. I tried to read the firmware (windows with STM8 programmer), but was not successful. I don't like these chips because we don't have all the tools under Linux, so I will replace it with another chip.

The temperature sensor is an K thermocouple type (specs of the station) and the small voltage is amplified with an LM321 opamp.

The 3 digit 7 segment display has his series resistors in the common anode circuit wich is not professional because we get different luminosity for different digits.

And here is the reverse engineered circuit :)


lora2mqtt circuit

Then I measured the voltage on pin PA1 (5) by changing the temperature

Temperature [°C] Voltage [mV] Temperature [°C] Voltage [mV] Temperature [°C] Voltage [mV]
110 663 210 990
20 378 120 698 220 1013
30 401 130 732 230 1045
40 431 140 763 240 1080
50 464 150 797 250 1111
60 498 160 831 260 1143
70 531 170 856 270 1176
80 565 180 889 280 1207
90 600 190 928 290 1243
100 630 200 958 300 1274

diagram temp voltage

Ok we got a linearity with about 3.2 mV/°C. After this I measered the PWM on pin PA3 (10) without heating. The ambient temperature is about 20°C:

Target temp. [°C] Duty cycle [%] Target temp. [°C] Duty cycle [%] Target temp. [°C] Duty cycle [%]
20 0 30 40 40 71
21 11
22 11 32 44
23 17
24 21 34 51
25 24 45 87
26 27 36 58
27 30
28 33 38 64 48 98
29 37 49 100

This can give us a hint for the PID regulation. Duty cycle increases about 3%/°C.

diagram temp dty cycle

Hardware

Software

Downloads

Everything is on github: https://github.com/weigu1/lora2mqtt_ethernet_gw.

Interesting links