T12 rapid heating soldering station for ATmega328P

Overview

Author: Stefan Wagner

Original project link: https://oshwlab.com/wagiminator/z-solderingstation-smd-v2

Open Source License: This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. ([ http://creativecommons.org/licenses/by-sa/3.0/](%28 http://creativecommons.org/licenses/by-sa/3.0/ %29 file) )

Function

The T12 rapid heating soldering station features

• Tip temperature measurement
• Temperature control via rotary encoder
• Short press the rotary encoder to switch boost mode
• Long press the rotary encoder switch setting menu
• Handle motion detection (by checking ball switch)
• Iron not connected detection (by identifying invalid temperature readings)
• Time driven sleep/off mode (motion detection) if iron is not in use
• Measure input voltage, Vcc and internal temperature of ATmega
• Information display on OLED
• buzzer
• Calibrate and manage different soldering tips
• Store user settings to EEPROM

Related Links:

• Firmware: [https: //github.com/wagiminator/ATmega-Soldering-Station](https: //github.com/wagiminator/ATmega-Soldering-Station)
• Project video: [https: //youtu.be/I9ATDxvQ1Bc](https: //youtu.be/I9ATDxvQ1Bc)
• Video from John Glavinos (electronics4all): [https ://youtu.be/4YDcWfOQmz4](https ://youtu.be/4YDcWfOQmz4)
• Video from LHW-createskyblue (UI-v1.6L): https://b23.tv/LiOe54
• A nice modification: https://oshwhub.com/222465.255411/atmega328p-han-tai

Versions, upgrades and notes

Soldering station v2.0

Soldering station v2.5

Soldering station v2.6

Interface upgrade

LHW-createskyblue has created a great upgrade to the user interface that can be optionally installed. It is characterized by:

• Beautify the details page and add a power bar
• Menu has icons
• Better scroll animation
• Get rid of the U8g graphics library and use the ArduBoy graphics library (Lite) to increase the frame rate, reduce memory usage, and make graphics possible
• Add flip display settings to adapt to different people's habits
• Knob direction setting menu
• screensaver
• Chinese and English language pack
• System password
• Better number input experience
• Chip overheating and low voltage alarm
• Watchdog timer automatically resets MCU

Notice

In board version 2.5, diode D1 may overheat. For safety reasons, the 18V zener diode D4 should be removed and the soldering station should be run at a maximum of 20V. Alternatively, diode D1 can be replaced with an SS54 Schottky diode, and BJT Q1 can be replaced with an FMMT619.

Power supply specification requirements

Select a power supply with an output voltage between 12V and 24V that can provide the output currents in the table below. The power supply must be stable. Current and power are determined by the resistance of the heater (R = 8 Ohm).

Temperature Measurement and Op Amp Considerations

The thermocouple (temperature sensor) is located in the T12 tip. It generates a very small voltage based on the temperature difference between the hot and cold ends (about 22 microvolts per degree Celsius). To measure this, the heater must be turned off since both share the same connection. The low voltage is amplified by the op amp and measured by the ADC of the microcontroller. The LMV358 is a very cheap and versatile op amp, but is not ideal for this task because it has a fairly high input offset voltage and is quite noisy. Although the SolderingStation will also work with this op amp thanks to the software's smoothing and calibration algorithms, I highly recommend spending a little more and getting a better one. For example, OPA2330AIDR or OPA2333AIDR have the same pinout and can also be used with this board.

Heater high-side switch for N-channel MOSFETs and charge pumps

The microcontroller turns the heater on and off via the MOSFET. Since the temperature measurement must be on the same line and connected to ground, the MOSFET must be placed between the supply voltage and the heater (high-side switch). P-channel MOSFETs are commonly used in this configuration. However, N-channel MOSFETs typically have low resistance (RDS (on)), which in the case of the IRLR7843 is only 3 milliohms. Low resistance means higher efficiency and lower MOSFET heating. In order for an N-channel MOSFET to function as a high-side switch, an additional circuit is required to maintain a positive gate-to-source voltage after the MOSFET turns on. This is done using a so-called charge pump consisting of a capacitor and a diode. The operating principle is shown in the figure below:

Building instructions

In addition to the components of the PCB, the following components are required:

3D printed housing aviation plug (4 pin or 5 pin, depending on your iron handle) DCDC jack (5.5 2.1 mm) switch (KCD1 15 10mm)

Make sure all parts fit nicely into the housing. Solder the wires to the connectors and protect them with heat shrink tubing. Use thick wire (AWG18) for power connections. Make all connections according to the schematic below, but remember that there is no standard pinout. Solder the wires directly to the corresponding pads on the PCB. To make the soldering station ESD safe, connect the ground (E) terminal of the pilot plug to a female DuPont connector and glue it into the corresponding opening on the housing. Now you can connect the soldering station to the ground terminal via the male Dupont connector. Upload the firmware and screw the PCB to the top of the case.

The pinout shown is for aliexpress's Quecoo handle. Different handles may have different pinouts. If you are assembling the handle yourself, follow the scheme shown in the picture below. This video by John Glavinos ( electronics4all ) shows how it's done.