RT Soldering pen

Soldering pen for Weller RT tips with OLED display

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Every hardware hacker need good soldering tool. My idea was to build own but with very specific qualities. On one side not so expensive, on second side high quality and also small with precise control and features. I found some projects where is used Weller soldering tips designed for WMRP soldering iron with standard 3.5mm jack and inside the tip is also thermocouple for sensing temperature. These tips are not so cheap but the quality is really great, especially for fine soldering. Hardware design is based on similar projects but with many modifications and improvements. Also my request was to make the hardware small as possible to fit into handle and capable to supply from hobbyist LiPO battery.
Buy one on tindiy:


  • very compact - will fit into handle
  • display show status, preset and tip temperature, power, supply voltage, drop, ...
  • two buttons
  • automatic standby
  • sensing supply voltage and tip current
  • precise regulation with PID (PSD controller with some modifications)
  • supply voltage is from 5V to 15V (best is above 10V)
  • designed to supply from LIPO battery 2S (7.4V max is about 18W) or 3S (11.1V max is more than 40W)
  • calculating consumed Wh
  • heat-up in 5sec from 25 to 400°C (with 40W limit)
  • Idle current about 8mA

What is planed:

  • case
  • battery monitor (warn when battery need charge)
  • configuration editor for some constants from PSD controller, power limit, ....
  • open-source everything


Portable Network Graphics (PNG) - 64.37 kB - 03/30/2017 at 19:45


  • 1 × STM32F031 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × AD8551 Precise operational amplifier
  • 1 × ACS711 Hall effect current sensor
  • 1 × LMR14203 Power Management ICs / Switching Regulators and Controllers
  • 1 × OLED display 0.91" 128x32

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Hikopan1972 wrote 11/12/2018 at 08:29 point

Hello !!

I want buy a soldering pen board but it seems out of stock now , will it be available soon ? Thanks 

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Branimir wrote 10/16/2018 at 10:40 point


Do you sell any naked PCBs?I'd like to assemble it on my own,if i have this option.

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Messschuh wrote 09/07/2018 at 19:18 point

got mine RTsp few month ago and i also have the TS100. the TS100 is OK for use at home with a notebook power supply or so, but for mobile use with 12 volt or a 4s lipo battery the performance isnt really great. i use the genuine rt weller battery solder since many years at work, i love this tool it works great, but for privat use it is to expensive. so i bought the RT soldering pen and i‘m really happy with it.  in my opinon it works better than the original one. 

i want to upgrade the firmware, still have V0.0.1 , but i have no idea how it works. bought the st link v2 and try to upgrade but i have absolutly no idea what to do.  is there any tutorial avalible  how to upgrade the firmware??? allready read the „“ at github but it dosent help me. so maybe someone have a link for a tutorial or can help with some helpful tips. ?

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Jarrett wrote 09/07/2018 at 19:26 point

hi Messschuh,

I'm not associated with this project in any way, but the directions look fairly straightforward (to me, someone who is comfortable with embedded toolchains).

Where are you lost?

It looks like there are two main components:

1. Physically hooking the STLink up to the soldering iron. There are pictures above on how to do it, and the shows the exact wires you have to connect.

2. Getting / compiling / flashing the firmware. Basically, with the STLink programmer connected, run all of those commands in the on the terminal. Only for Linux / Mac, Windows would have a very different (and not recommended) workflow

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vlk wrote 09/07/2018 at 20:58 point

Hello Messschuh, thanks for asking, that is true that I don't have very detailed tutorial to update firmware (for non-programmers), I will improve it!

For now you can download the compiled version of firmware (.hex or it will work also with .srec or .bin) from github:

so you don't need to install any toolchain and build it.

Then if you are on windows you can download clickable flashing tool - stlink-utility from ST: (probably for download you need to register into

And with this utility you can flash the new firmware. it is easy and safe, but I suggest you to remove the soldering tip before updating and if the firmware will run successfully (also check the version if is v0.2.0) then connect the tip and test it.

So, if you will have any problems, send me email or private message and I will try to help you directly.

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Messschuh wrote 09/08/2018 at 11:39 point

wow, thx guys for fast answer . 

about the wiring, that isnt my problem. im not „stupid“ at all,  i can programm an arduino, i can programmm a cs 8635 bluetooth receiver and so on...., but i still have no experience with the st. maybe i can do a tutorial when i check how it works.  luv this project, and would be happy if i can support it.

 thx again for quick response guys u are awersome.

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Messschuh wrote 09/10/2018 at 16:02 point

OK, got it. Downloaded the ST tool and the hex file the rest was self-explaining. It`s so easy if how to know. :)

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Otto Winter wrote 08/29/2018 at 14:30 point

The new case is born!
In the next days the STL Data, for 3D printing would be available...
Here is the "perliminary" picture:

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Jan wrote 08/29/2018 at 20:36 point

That background! Can you add a space cat surfing on the handle as well? Would be awesome. Jokes aside: that looks really comfortable to hold and work with. Nice job!

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Otto Winter wrote 08/29/2018 at 22:53 point

Thank you, sorry, a white background looks really bad ;-)

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nickwrgggdd wrote 08/31/2018 at 00:04 point

Otto that case is amazing to you actually have that DC cable can you link me to it?

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nickwrgggdd wrote 09/03/2018 at 16:47 point

otto have you printed a prototype of your design yet idk if 3d printing is the way to go what method do you recommend using to print that. What your going for it might be better to get a bunch injection molded and have vlk sell them with/ as addon to his pen. I just dont know what wuld be the best way 

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JaneDoe wrote 09/04/2018 at 16:28 point

I seem to remember injection moulding beeing Very Very expensive...

That's why we have a 3D Printing industry going ;)

Otto's render of the case look stunning.

Just got a RT tip for my controller, d*mn this thing heats up fast :D

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Otto Winter wrote 09/06/2018 at 11:34 point

I let it 3D printed with MJF (SLS like) method by
Two complete cases for 35€. Yes it was not cheap...
If you have a good 3D Printer, you can try to print it yourself.

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Messschuh wrote 09/07/2018 at 19:22 point

really nice work otto,  when the stl is avalible i will try to print it with my fdm printer.

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nickwrgggdd wrote 09/29/2018 at 04:08 point

Otto ETA on STL data??

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Arne Wichmann wrote 08/25/2018 at 14:57 point

I designed an experimental Housing:

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vlk wrote 08/25/2018 at 20:09 point

Hi Arne, it is very original design, nice! thanks for sharing it.

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nickwrgggdd wrote 08/26/2018 at 08:30 point

Hey thanks for sharing the design i got this part printed using SLS for 22.26 at sculpteo it would of been cheaper but i got polished finish will post pics when it arrives they were the cheapest i found if anyone else is intrested

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Arne Wichmann wrote 08/27/2018 at 14:16 point

I just noticed that I had a bug in the design (measured from the knob of the buttons, not the corner of the button housing). I have fixed it on Thingyverse. Maybe you can still change your order? (My print of the buggy design still worked, but the buttons were quite off...)

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nickwrgggdd wrote 08/27/2018 at 16:08 point

i was able to update design as it was printed yet guess im lucky i ordered on a weekend again thankyou so much

*Also have you printed this? Mind posting pics?

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Arne Wichmann wrote 08/27/2018 at 17:03 point simple black PLA-extrusion print, with bad light conditions :)

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Arne Wichmann wrote 09/05/2018 at 15:07 point

I have tweaked my design a bit:

(Currently untested.)

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nickwrgggdd wrote 08/24/2018 at 22:35 point

confirmed xbox 360 powersupply powers it perfectly

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nickwrgggdd wrote 08/19/2018 at 22:47 point

For anyone wanting to use somthing other than lipo to power this an xbox 360 slim power supply should work quite well the can be found quite cheap on ebay. NOTE I have not tested this yet but was informed by other that this psu can support the high 6-8 amp pulsing. and i will be using a xt30u connector to make a nice connection while still maintaining portablity. I will update later this week when i recieve the psu. 

Also Otto Winter i dont know what type of connector your incorporating to fit with your 3d print design but alot of lipo batterys come with xt30 or jst xt30 supports higher amp rating without getting to hot

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nickwrgggdd wrote 08/19/2018 at 22:54 point

only reason i thought of xt30 was w/ a case i think it would make a nice snug connection rather then just placing a jst over the 2 prongs

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Otto Winter wrote 08/15/2018 at 09:16 point

The new Firmware V0.2.0 working fine with  LiPo 4S 3000mAh (14,8V) !
Thank you :-)

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nickwrgggdd wrote 08/01/2018 at 14:03 point

hey just wana make sure this pen doesnt have to be powered by a Lipo battery correct? Im planing on using a 12v or 14v 3amp power supply if im reading correctly that should work itll be about 42w

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vlk wrote 08/01/2018 at 20:05 point

Hello, it is not easy, because it has pulse current, with peak dependent on supply voltage, peaks are short but they are at 12V 6A or at 16V 8A. although the current is high average power will be at maximum 40W, so if the supply will have strong capacity bank, it will be work.

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Otto Winter wrote 07/27/2018 at 15:39 point

I've found something that can kill the RT Solder Pen!
If somebody do not pushing the RT Pen full in the socket, you do not have any values from thermostat and the pen glowing with orange color !!!
In the software, you should prevent heating the pen, without sensing the thermostat resistance!
Best Regards

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vlk wrote 07/27/2018 at 19:00 point

Hi Otto, thanks for reporting, I have in software this state but detecting code is not implemented right now, so this is good reason to do this.

Hope your RT TIP survive this shock.

There is also other problem if somebody connect supply in reverse and TIP is connected, then MCU is protected by diode, but TIP not (due to large drop voltage on diode) and it get full power through diode inside MOSFET.

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Otto Winter wrote 07/27/2018 at 23:21 point

My RT TIP is Ok because I did disconnected it fast enough...
For the revese power connection I don't see any solution, because of no place for such high current protection circuit!
The user should look for the correct polarisation of the Power connection...
You can put one 10-20A shottky diode between plus and minus wires.
If the User connecting it wrong they get only a short circuit and your controller is saved from burning out.

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Otto Winter wrote 07/27/2018 at 12:33 point

Hello, now I got your new Board and it is perfect and working well!
In the next weeks I'll change my prior designed enclosure and give it free for 3D printing here.
Best Regards

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vlk wrote 07/27/2018 at 19:04 point

Hi Otto, thanks for the order and also big interest to create enclosure, we will looking forward for the design, thanks!

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nickwrgggdd wrote 07/24/2018 at 00:23 point

Where are the Solder Points on the board for Programming the STM32

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vlk wrote 07/25/2018 at 08:56 point

These pins are near to MCU in middle of PCB and marked G, C, D (GND, CLK, DATA).

Look on these pictures:

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ivan003003 wrote 06/29/2018 at 14:02 point

Hello there Mr.vlk

I have read carefully the technical characteristic of your RT Soldering pen.

I'm really in love with it and i'm very excited to buy it,at least one :)

However,for me the only one problem is this : 

i can't go to buy this item raw as it is now!

without any kind of enclousure and an incorporated power plug.

I really hope that you & Otto Winter will release the RT soldering pen in final version,with the enclousure and the incorporated power plug.

Thanks you very much !

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vlk wrote 07/08/2018 at 05:37 point

Hi Ivan, enclosure is planed

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ivan003003 wrote 07/10/2018 at 17:47 point

I'm very,very glad :)

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[this comment has been deleted]

vlk wrote 06/26/2018 at 10:46 point

No, it is not a clone, it is completely created from scratch (HW and SW), it uses different MCU, also have current sensor, for better diagnostic and more precise regulation and also it can operate at lover voltages, faster heating (4s). Also biggest advantage are Weller tips, and is made in EU. On other side there is no USB.

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Rens wrote 04/14/2018 at 00:09 point


very nice project, any plans to make the PCB available.

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Albert Green wrote 03/14/2018 at 20:04 point

Are you using the I2C version of the 128x32 OLED display? Where do you buy it? I cannot find a source for it. seems to sell only the SPI version. And on Aliexpress/ebay the I2C version seems only available soldered on an adapter PCB.

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vlk wrote 03/26/2018 at 06:15 point

Hello, there are also on ebay:

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Bodzio wrote 02/15/2018 at 18:03 point

You have a bug in the project. Weller uses a D-type thermocouple in the tips no K-type !

K type thermocouple in 500 'C has voltage 20.644 mV, but D type 8,077mV.

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vlk wrote 02/15/2018 at 22:45 point

Thanks! You right, The equation is hope correct, but the type of the thermocouple in schematic is wrong. I will fix this.

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Otto Winter wrote 02/07/2018 at 16:25 point

It looks very good, if you get it running, please tell me, how can i get 1-2 finished PCBs!
Best Regards
Otto W.

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Paulo Bruckmann wrote 02/06/2018 at 13:38 point

I'm amazed how you fit all in that size, I am guessing you used 4 layer board. I'm designing  one for Arduino with usb ,accelerometer , buzzer (take a look at my profile).  My problem is that  a ts100 for 45$ and I I'm aware that is not the same thing. But this is the price of one RT tip :/ . 

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vlk wrote 02/06/2018 at 19:13 point

Hi I saw your version, nice renderings and also case.

Regarding PCB, yes! it is 2 (TWO) layers, design was not easy and I spend lot of time optimizing for high current. Most problematic was ground to keep it strong from one side to another.

TS-100 is nice, but Weller tips are TIPs and if anyone at least once tried Weller then he know that soldering with that is quite different (better). TS-100 is also heavier and bigger, tip is also longer and not so good for very precise soldering. Also need higher voltage for work. (for RT only 12V with 50W and is working from 7V with 18W)

Cheapest Weller station cost more than €300 ?

RT tips are in discount, so the price is now quite better.

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Paulo Bruckmann wrote 02/06/2018 at 19:56 point

I don't own a weller RT tip yet, neither a TS100, but already worked with other weller irons. I wasn't sure if it is going to be a big difference. The parts and labour seemed to be an investment.
But now that you print me out the picture, I may continue the project. I always wanted a mobile friendly soldering iron.

Oh! It's 2 layers! You got skills, and I know what you talking about when you say optimizing! What was the minimum footprint, 0603s?  I may switch my 0805s resistors to 0603s. I also using the oled version of 11 pin

I let the power traces without solder mask so they get solder tinned in the fabrication.

I use kicad, if you have the all parts in 3D ( I designed the display) it renders in realtime, it's mind-blowing, isn't it? You don't believe it but my last board layout was built from scratch in less than 2 hours. push  & shove power! 

Thank you for your Reply . Regards!

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HP (@banjohat) wrote 02/06/2018 at 13:33 point

Interesting! This reminds me of my own project ;)
Out of curiosity - how did you end up with that mini-jack?

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vlk wrote 02/06/2018 at 14:38 point

Hi HP,


Yes I know your project, my is inspired by yours and also other similar projects (but desktop versions) and also by TS-100.

About JACK connector, I changed the connector to another because this one needs thin plated slots which was problem with many PCB manufacturers, or it was too expensive.

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HP (@banjohat) wrote 02/06/2018 at 14:40 point

Very interesting! I kept that one because I really favoered the co-planarity of the connector. However, I haven't been able to find anything rated for 2A which is needed by the tip. I guess that's not a problem for you if you use another one - is that still co-planar?

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vlk wrote 02/06/2018 at 18:47 point

The connector is and it has two spring contacts and also two pins for ground then two contacts and pins for TIP (heater) and one for mid pin (sensor) so, I think this will be better. So if one contact is rated for 1A then two contacts can transfer 2Amps. and I don't connect under high current, so static current can withstand much higher. Previous version with old connector (on picture) I checked with IR camera and the connector was cold, hottest place was BUCK converter, MCU and chip on OLED display.

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René Arts wrote 06/26/2018 at 15:17 point

If you would want to improve the connector; I have found a nice one which is rated for 5A continuous: search for FCR1295 S9/BBB stereo 3.5mm mini jack socket, it is available i.e. at Conrad and Farnell. Nice project by the way, I'm thinking of buying one!

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