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 18V (best is 10-13V)
  • 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



RT pen case bottom part for HW v1.0

Standard Tesselated Geometry - 9.53 MB - 12/08/2019 at 19:15



RT pen case Top part for HW 1.0

Standard Tesselated Geometry - 4.78 MB - 12/08/2019 at 19:15


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

  • Display replacement

    vlk05/02/2023 at 09:25 0 comments
  • New HW revision v1.1

    vlk02/08/2021 at 21:00 0 comments

    - new switches

    - updated layout with fixed current sensor connection bug


    vlk12/08/2019 at 19:22 4 comments

    Otto Winter send me STL files with case design for HW v1.0

    Bottom part: Weller-RT6-Holder-Bottom-V1.0.stl

    Top part: Weller-RT6-Holder-Top-V1.0.stl

  • About new RT tips

    vlk12/08/2019 at 18:55 0 comments

    RTM, RTP and RTU tips

    Weller this year introduced new series of RT tips with nice slogan "No compromise".

    There are three types:

    • RTM - RT Micro - they are same like previous line RT, but with new naming
    • RTP - RT Pico - these tips are smaller, shorter for more precise soldering
    • RTU - RT Ultra - these tips are in opposite bigger and designed for higher power (till 150 Watts)

    All the tips have same pinout and in general are compatible,

    RTM and RTP (also previous RT) have resistance of heating element 2 Ohm and they are designed for 12 V (current is 6 A) but maximum average heating power is 40 Watts - this power is controlled and limited by PWM.

    RTU has resistance of heating element 3.5 Ohm, this mean, to reach 150Watts is necessary to use higher voltage - at least 24V, but the current will be still similar - what is good for the JACK connector.

    But actual design of RT soldering pen has limitation for power at 18 V and current to RT, RTM and RTP will be at 18 V: 9 Amps - the pen it should withstand it, because average pulse power is limited by SW to 40 W) question is what can withstand the JACK connector.

    The main question is how to use this with RTU tips they need 24 V. so, absolute maximum rating of HW 1.0* is 25V for supply voltage (limiting element is input capacitor) after replacing input cap next limit will be 30V (maximum voltage of MOSFET switches)

    *Absolute maximum rating for previous HW v0.3 is 20V - this is limited by 20V MOSFET switch.

    For RTU if the supply will be 24V then output power can be near to 150 Watts, but this need also modifications in SW to allow higher output power. Yes, this is planed and new release will available be soon.

    Another problem with new tips is that each kind RT/RTM, RTP and RTU has different dimensions of the cylinder on JACK side and is necessary to count with this for case design. (old RT and new RTM have same dimensions of the cylinder) this is also reason why Weller sell for each kind different tip holder.

    MS tips:

    If I talking about tips there is one more question: What it mean if in name is "MS", it mean that tip meets Military Specifications. But there is no more informations. In general the main different is that shield of the tip is electrically isolated from the connector, standard tips have shield connected to ground.

    Weller RT TIP typemax average powerheater element resistancecurrent  and power at 12Vcurrent and power at 16Vcurrent and power at 24V
    RTM / RT40W (55W*)6A / 72W8A / 128W-
    40W6A / 72W8A / 128W-
    RTU150W3.5Ω3.4A / 41W4.6A / 73W6.8A / 164W

    * some RT tips have 55W limit (RTM 36 S / RT 11)

    from left: RTP, RTM, RTM MS, RTU

  • New RT tips

    vlk10/06/2019 at 20:14 1 comment

    just found, that Weller announced new RT soldering tips

  • New firmware v0.4.0

    vlk10/06/2019 at 20:06 0 comments

    New firmware is ready to download, it support HW v0.3 and also new HW v1.0.


     - display brightness control

    - turn off display to protect pixels burning when is inactive for 15 minutes (wake up by pressing both buttons at once)

    - increased maximum preset temperature to 500°C (only for HW v1.0)

  • New redesign is ready

    vlk09/26/2019 at 18:30 1 comment

  • New HW

    vlk05/07/2019 at 18:36 3 comments

    After longer delay, after some troubles, new revision is getting ready.

    There will be two major enhancements:

    • full reverse polarity protection
    • added accelerometer

    Stay tuned..

  • New version of Firmware v0.2.0

    vlk08/09/2018 at 18:14 0 comments

    Main changes:

    - improved PID

    - saving preset temperatures

    List of all changes and download:

  • New version of Firmware v0.1.0

    vlk07/24/2018 at 21:29 0 comments

    Although is still in development state is stable and has many new features, like simple main screen with large temperature, Fahrenheit mode or left-handed mode.

    There is also many features in background

    Update is easy and safe with any SWD (ST-Link) programmer

    Download from github:

    Updating firmware with cheap Chinese ST-Link programmer:

    To program, use ST-Link utility from ST, or any other SW for Flashing STM32 micro-controllers (openocd, texane/stlink, pystlink, ...)

    There is also possible to use ST-Link part of any Discovery or Nucleo board.

View all 18 project logs

Enjoy this project?



REI wrote 01/21/2024 at 22:04 point

Does anybody know if something happened to VLK? It's like he is disappeared..

  Are you sure? yes | no

jkykayex wrote 09/10/2023 at 01:33 point

For anyone 3D printing the case, its quite hard to print properly and is weak around ports. 

I have made a case for this which is solid around both ports. It is designed to work with a USB-C PD trigger to feed the PCB or can allow 2 wires to be fed in, has protection for buttons, flat top and bottom so it doesn't roll and is held in with 4xM2 hex screws. Is designed such that buttons are not accidentally actuated and is safe for plugging in and unplugging the tips. 

the LCD cutout is plenty deep for extra protection.

I currently have it printed in PETG as my draft and is great, the final drafts are being made in MJF PA12-HP Nylon (170°C) print. 

If anyone is interested, I'm happy to sell some of these cases once I get the final draft back. 

The current drafts look like this:

  Are you sure? yes | no

toby wrote 07/26/2022 at 16:24 point

Hi! I love this pen, I bought it a few years ago and it's done lots of great work. However, one of the switches became flaky. I am going to attempt replacing them. Is this the right part? there is a slight difference in part number from the schematic.


  Are you sure? yes | no

toby wrote 01/01/2023 at 23:16 point

For others: These are apparently the switches.

Unfortunately after replacement, my pen is dead. So I'm looking hard for a replacement that can use the Weller RT tip.

  Are you sure? yes | no

Martijn Schouten wrote 02/28/2022 at 20:18 point

Hi thank you for designing this great product, I love it, it solders really well. I have made a case for your PCB that can be easily printed on a normal (FDM) 3D printer. The source files can be found on:

  Are you sure? yes | no

vlk wrote 03/01/2022 at 13:59 point

Martijn, great job, thanks!

  Are you sure? yes | no

johnsfuller wrote 04/11/2021 at 12:09 point

Hi Vik, thanks for making such a cool product, much respect! I do most of my soldering where there isn't AC power and storage space is limited, so this is an amazing tool for me.

I think I'm forgetting something on how to use:
- I tried to use my soldering pen(HW 1.0, SW 0.40) for the first time in a couple of months and something is wrong. 
- When I hit a button to start the heating, the display goes blank for a second and then comes back on, but no heating and 0Wh.
- On AC power, I tried 7, 9 and 12v supplies, no change.
- switching tips also didn't help

If you or anyone else has run into this I could use some help. 

  Are you sure? yes | no

Manu wrote 09/08/2020 at 10:07 point

Hi, I made myself a soldering iron based on your pcb. It works nicely! Do you know if it is possible to use Weller RTW SMD tweezers with this design? (I was wondering this because of this project: that you might already know)

  Are you sure? yes | no

nirh216 wrote 08/27/2020 at 23:28 point


It seems a mighty well project! Well done. 

Can you please share the schematics for the HW 1.0 (or newer)

I want to buy all the components and build one for myself. 

The current schematics mentions a different smaller OLED screen while in Components section it says it has a larger one.

If you could also share the board pcb design as well, it would be great (dimens, layout, etc..)


  Are you sure? yes | no

Azanot wrote 07/27/2020 at 17:29 point

Dear Vlk, thanks for your support. I ran the tests you suggested and the result is the following:

1st Test
Power supply: 8V
Tip: RTM 002 C (Old RT 1)
All values are perfect and correspond to your indications.

2nd Test
Power supply: 12V
Tip: RTM 002 C (Old RT 1)
All values are perfect and correspond to your indications.
( Please watch attached video: )

3rd Test
Power supply: 8V
Tip: RTP 001 C (New RT PICO)
All values correspond to your indications but the set temperature has a long time to stabilize (Compared to old tip RT 1)

4th Test
Power supply: 12V
Tip: RTP 001 C (New RT PICO)
All values correspond to your indications but the set temperature has a peak of + 30/40 ° and has a long time to stabilize. (Compared to old tip RT 1)
( Please watch attached video: )

Is possible that these temperature peaks of + 30/40 ° (compared to 4/5 ° on the old RT1 tip) could have broken the heating element of new tips? Why these temperature peaks? I await your precious opinion?!

Thanks for your help ; )

  Are you sure? yes | no

vlk wrote 07/27/2020 at 18:24 point

Hello, RTP tips are very tiny and the constants for PID regulation loop should be corrected, I have plan to fix this, or by selecting in menu

  Are you sure? yes | no

Azanot wrote 07/27/2020 at 21:59 point

Can you indicate the values in the firmware to be changed or modified for perfect use with RT PICO tips?

Thank you

P.s. Have you seen the videos I have published?
Have you noticed any hardware malfunction?

  Are you sure? yes | no

vlk wrote 07/28/2020 at 08:40 point

Hello Azanot,

Yes, I have seen your videos,

I have noticed same unstable regulation after testing RTP tip, as I mentioned, there is necessary to update PID constants

I don't have enough time at the moment to tune the PID regulator for RTP tips, I can only promise that I will try to work on it as soon as possible.

If you have experience with SW dev, you can try this alone. Changing constants is possible in source code here: but be very careful, you can easily broke the tip with wrong constants. I have spend really lot of time to tune this regulation loop.

please send me email to pavelrevak at gmail if you need more help.

I would like to mention that you use too high temperature, for normal soldering is enough to use 300°C, because 400°C can degrade the tip faster, personally I use 250-300°C (rarely 350°C) depends how thermal area is around soldering place.

  Are you sure? yes | no

Azanot wrote 07/23/2020 at 16:54 point

Dear Vlk, I writing to report a strange case, detected on HW 0.3 with new RTM tips.
The welder "broke" the heating element on 3 RTM tips, model: RTM 013S TIP (T0054460399N)
The 1° tip: broken after 30 seconds, set temperature 400 °
The 2° tip: broken after 20 minutes of use, set temperature 350 °
The 3° tip broken after 1 day (with brief discontinuous use) Temperature 300/400 °
All three tips after use result broken to a heating element with a value of about 29 Kohm.
All the tips were new and sealed. (Different production lots)
N.B. Old RTM tips work well
Is it possible a safety system in new RT tips that burns heating element for non-original stations? What is your opinion?

HW used: 0.3

FW used: v0.4.0

Power supply: 12V Stabilized

I await your response
Thank you

  Are you sure? yes | no

vlk wrote 07/23/2020 at 21:14 point

Hello Azont,

it is very interesting, there can be two problems, first is that the regulation is not working correctly due to something broken on PCB of RT PEN

Or the TIP is not fully inserted into the jack, then sensing of temperature is wrong and it sends full power to the RT tip.

Didn't you notice that the tip glowed orange before it breaks? this mean that is overheated.

  Are you sure? yes | no

Azanot wrote 07/23/2020 at 22:51 point

Dear Vlk, please read more carefully my previous message.
I insert the tip fully, with carefully and no sign of over heating has occurred.
(No glowed orange)
I will use 2 other RTM tip (Old version) without problems.

Can you suggest me some tests to do on electronic hardware?

I burned the heating element on 3 new tips, all were RTM 013 S (T0054460399N)

Thanks for your patient attention ; )

  Are you sure? yes | no

vlk wrote 07/24/2020 at 07:30 point

Ok, regarding some tests:

1. use lower voltage (about 7-8V)

2. set lower temperature - e.g. 100°C

3. turn ON and check tip temperature and actual heating power (in right - up corner)

4.a if the power will be still too high or temperature still low, then it should be problem somewhere in HW. (immediatelly turn it OFF) - stop here

4.b temperature should be stabilized to 100°C and during this the power should be less than 1W

5. check in menu measured heating element resistance, it should be around 2ohm - in this case is HW OK

6. 12V and higher temperature (200°C - power around 1.5W, 300°C 2.5W)

7. repeat this with 12V

if HW will be OK, then probably are problems inside tips - you can try reclaim them.

hope it helped you.

  Are you sure? yes | no

vlk wrote 07/27/2020 at 18:37 point

I don't think that there will be some 'safety system' from my point of view are probably these tips just wrong (wrong series). I broke some tips but I daily use RTM tips RTM008C and RTM002C and never see these issues.

In RT PEN is regulated and limited output power by PWM, so, if you use higher voltage, then PWM will generate shorter pulses to keep output power at least 40Watts.

HW 0.3 and HW 1.0 has largest difference that allow to set/measure higher temperatures and use higher supply voltage. but HW 0.3 has for example more precise temperature sensing OP-amp.

Yes, I broke some tips, but it was during SW development, because I overheat these tips by mistake.

  Are you sure? yes | no

shodid wrote 06/10/2020 at 00:56 point

I would like to see the priority on accelerometer, sleep/wake, battery protection/indicator, and usb power delivery with lower voltage mode so I can make use of my many common Li-ion batteries.

I am not sure the big power and ultra size tip compatibility seems worth it. So many changes for different jack size, power, and thermal concerns with the current design, but I am not the one needing/wanting big power in this compact size.

I like this project for a lightweight and convenient portable option, but of course, this is up to vlk where he likes to to focus efforts.  Thanks to you vlk whatever you decide!

  Are you sure? yes | no

GreekGeorge wrote 06/01/2020 at 18:19 point

Will v1.0 PCB files be open sourced?

  Are you sure? yes | no

Azanot wrote 05/26/2020 at 23:38 point

Thanks for your attention and clear answer.

I have another little question please.. :-)
Why in HW 1.0 the maximum temperature is 500° but in HW 0.3 is limited to 400° ?
Hardware 0.3 does not support temperatures over 400° ?
If yes, why you limit it to 400° ?

P.S. I hope in the next firmware you make editable from the menu "standby  timer" and "display OFF timer" which are very useful.

  Are you sure? yes | no

vlk wrote 05/27/2020 at 09:17 point

Hello, yes, it is because on v0.3 has different resistor divider and maximum measurable temperature is around 500°C (regulation cannot exceed 400°C) and on v1.0 is around 1000°C, limit to 500°C is from reason to protect the soldering tip.

There is way to replace certain resistors and change FW.

FW features: yes I have this in my TODO and also other thinks, but currently I have limited time to work on this project, but hope soon I will have more time.

  Are you sure? yes | no

Azanot wrote 05/26/2020 at 16:28 point

Hi vlk, congratulations for your wonderful project.
I have 2 questions please
1) What functions you have added on HW 1.0 with gyroscope ?                                                     2) is it possible to install the same gyroscope on old HW 0.3 ? (You can publish one installation scheme ;) For the people who purchased HW 0.3. This is to reassess and equalize HW 0.3 to the new 1.0


  Are you sure? yes | no

vlk wrote 05/26/2020 at 18:26 point

Hello Azanot,

thanks for asking

1: gyroscope is not currently used by SW, planed is in next releases for detecting free fall and or for wakeup,...

2: yes, it is possible but everything is so small, probably with some gyro module. and currently it has no sense while is not used by SW ,-)

Personally I don't need the gyro, there is automatic turning off by detecting if you do not solder and wake up is not necessary, while it heat-up in 4 seconds, ok I need to press button before..

  Are you sure? yes | no

Andre Idoffsson wrote 05/08/2020 at 16:03 point

Hi awsome project! Do you know if/when it will bee restocked at tindie again? 

  Are you sure? yes | no

Andreas Kahler wrote 01/07/2020 at 15:52 point

Awesome project, Pavel!

Will there be PCBs available on Tindie anytime soon again?

Alternatively, I think about building one myself. Did not see board/gerber files for the current version, though. Do you mind adding them to github? Thx.

  Are you sure? yes | no

vlk wrote 01/09/2020 at 06:44 point

Hello Andreas, thanks for interest, everything is restocked back

Manufacturing data will be shared later, currently you can build older revision.

  Are you sure? yes | no

Fiddl3 wrote 01/07/2020 at 09:48 point


Can anyone tell me if I can use TC55RP3302ECB regulator instead of LMR14203?

  Are you sure? yes | no

TheLocalPenguin wrote 12/30/2019 at 17:54 point

I just received your soldering iron. Works like a charm - Thank you for making it!
If anyone out there is unsure about buying it, I warmly recommend it. Cheap, and quite effective.

  Are you sure? yes | no


[this comment has been deleted]

ronwang1215 wrote 02/25/2020 at 06:38 point


- uses weller rt tips which got very good heat-recovery performance (much better than T12, almost as good as jbc tips).

- many different tip geometry to choose.

- portable and have a wide range of input voltage.


- no case and other accessory for now.

- doesn't want to use other irons after using it.

  Are you sure? yes | no

Chris Roberts wrote 12/06/2019 at 11:23 point

I Just bought one of your controllers and I'm looking forward to using it. I am just thinking about a case and looking at the RT tip that I have here, Do Weller hold the tips in with a ring magnet in their official hand-pieces?

  Are you sure? yes | no

vlk wrote 12/13/2019 at 16:01 point

Hello Chris, Thanks, Case is available for download. I don't know nothing about magnet in original Weller hand-piece.

  Are you sure? yes | no

vlk wrote 12/13/2019 at 16:21 point

be careful if you wan't add magnet, because the magnet can influent the current sensor, which is HAL-based, although if there is compensation for surrounding magnetic field, large error can stop correct measurement.

  Are you sure? yes | no

antop wrote 10/16/2019 at 10:37 point


Congratulations vlk for the job.

I have a doubt I am manufacturing my own PCB, which connector do you use for the display connection? Can you show an example of how you assemble the screen with the PCB? 

Kind Regards.

  Are you sure? yes | no

vlk wrote 12/13/2019 at 16:24 point

Hello antop, I don't use any connector, display is directly soldered to the PCB and glued with double-sided adhesive tape (1.5mm thick)

  Are you sure? yes | no

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