Internal Soarer's Converter from scratch (beginner friendly)


21 May 2018, 11:04

Hi guys! This guide is for absolute beginners and is a step by step guide on creating an internal Soarer's Converter. For reference, here's the end product:
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This adaptor is designed for IBM's Model F but can definitely be re-purposed for other keyboards. It's powered by a Pro Micro (Teensy clone) with 4 Dupont male pins leading out of it allowing you to plug and play into an IBM Model F. It can then be followed by a MicroUSB Cable of your liking.

Please PM me if you have queries. I'm active on geekhack as well.

I also hand make these adaptors on eBay and I ship them worldwide. PM me if you're interested :D

First, a list of material:
Pro Micro
Male to Female Dupont Cable
Black Electrical Tape
Heat Shrink Tube
For the Dupont cables, we just need 4. Alternatively, you could get any wires you want, but it'll make it much harder to plug into the Model F. For the Heat shrink tubing and black tape, it's not necessary, but it'll make things more sturdy and prettier.

Obviously this requires a soldering iron and some other equipment like scissors and a pair of steady hands. :lol: This is also written for Windows.

Alrighty, next step.

Flashing the converter:

1) Install winAVR: 2) Download Soarer's converter: Download the v1.12 update which contains the firmware only. Download the other attached files for documentation and other tools.

3) Get ready the Pro Micro:
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4) When you plug in the Pro Micro, Windows should see a COM device under device manager, the exact COM port differs for everyone:
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5) Open a command prompt and navigate to the firmware folder which contains the hex files. Mine's located in my documents folder.
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6) Now, use something metal to short the GND and RST pins on the Pro Micro while it's plugged in. Personally, I just use a metal scissors.
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7) Immediately on Windows, the COM port should change and detect a new device with a different COM port.
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8) On command prompt, type in the following commands:

Code: Select all

avrdude -p atmega32u4 -P COM5  -c avr109  -U flash:w:Soarer_at2usb_v1.12_atmega32u4.hex
Change the COM5 into the COM Port that shows up on your computer.
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9) If it times out (you have a buffer of about 5s before the Pro Micro resets itself), short the pins again and type in the command again. I personally type the command before hand and press enter when I short the teensy.

10) If the firmware is successfully flashed, you should see this:
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11) Under device manager, there should be no more COM Ports and you should see a Soarer's converter in the devices panel in control panel.
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Yay! You've flashed the firmware successfully!
Now onto the next part, soldering and making the converter:

1) You'll need 4 Dupont male to female cables. I've got 4 and they're about 5 inches long.
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2) I used a plier to bend the male pin into a right angle as it makes soldering much easier.
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3) Now get to soldering! I have a helping hand so I can clamp the cable down on the board and the right angle sticks the pin into the hole.
The pins to solder is: 2, 3, GND and VCC. For GND, there are a few that you could use but I recommend using the one along the side of the VCC.
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4) Snip off any excess solder which might affect soldering:
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5) Solder the rest of the cables!
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6) The end result:
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7) Time to test the Pro Micro! I'm using a Model F XT here:
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8) To figure out which pins lead to which, use to find out the pinout. You'll need a multimeter for this. I made a simple diagram to follow:
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It's not the best illustration, so here's a written explanation:
Use a multimeter to figure out which pins of the DIN connector (Model F XT for example) leads to which pin on the actual board connector and use the keyboard pinout documentation as reference. I'll leave the Model F XT and 122 pinouts here:

Code: Select all

Model F XT: From back of keyboard (metal plate)



Code: Select all

F 122 Connector view:


9) Time to wrap the adaptor up! At this point, the adaptor is completely functional so if you wanna stop here and start using, it's done. I'm doing this part to insulate the adaptor. I'll be wrapping it up in insulating black electrical tape followed by heat shrink wrappings.
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10) Electrical tape:
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11) Heat shrink wrapping, you can use any heat source to shrink it:
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12) All done!
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It's done! This section is showing off some pigtails and female USB mounts.

1) Female pigtail:
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2) Mounting the female USB onto the board:
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This is a magnetic microUSB cable I sourced, allowing me to attach and detach magnetically.
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MicroUSB female mounted into a Model F AT.
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Model M50 with a USB-B female mounted into the case.
2 Pictures of my current collection :lol:
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Model F XT, IBM 3727, Model F 122
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workshop-f7/how-to-use-a-pro-micro-as-a ... t8448.html
Last edited by xueyao on 22 May 2018, 17:00, edited 2 times in total.


21 May 2018, 11:21

Fantastic guide!! Thanks for writing it up!

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21 May 2018, 11:29

Awesome guide!

Oh, your beamspring has the right shift upside down. Fortunately there's a back-up key right above it.


21 May 2018, 11:44

Iggy wrote:Awesome guide!

Oh, your beamspring has the right shift upside down. Fortunately there's a back-up key right above it.
It's actually a selectric shift key, couldn't fit it into the normal way but fits perfectly upside down haha

Sent from my SM-G965F using Tapatalk


21 May 2018, 20:53

Great guide! Bookmarking it now.

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ISO Advocate

21 May 2018, 23:03

Great to have it all in one place! Thanks for sharing, that is reall helpful. Used to do a few mods like this myself and always had to check five different threads for pinouts and firmware stuff.

Edit: my mods were never that good looking. I usually just hotglue the promicro into the case and add a short USB extension cable

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21 May 2018, 23:08

Man, I love that USB-B full size connector. Well done.


22 May 2018, 08:29

Amazing guide! Can this be added to the "Threads Of Interest"-thread?

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ISO Advocate

22 May 2018, 15:16

I would like to add two other helpful threads for IBM conversions:

workshop-f7/ibm-terminal-es-to-us-iso-l ... t9745.html

workshop-f7/ibm-model-f-122-key-termina ... 11102.html

Hope it's appreciated :)

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20 Sep 2020, 00:04

I'm just here to say, "Thank you for this thread." This worked great. I'm going to put up a couple updated parts in a few.

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20 Sep 2020, 00:50

All Amazon links.

ARCELI Pro Micro Atmega32U4 5V 16MHz. $8.
EDGELEC 120pcs Breadboard Jumper Wires. $7.
A micro USB to USB 2.0 cable. $7 for 5.
Electrical tape.. Under $3.50.

Other stuff ...
Soldering iron of your choice with a small tip for electronics. I got a decently reviewed one that was on sale for $70. (Hakko brand is supposed to be the best, but costs $60 more.)
"Helping Hands" / "Third Hand." This one also held my magnifier. $19.
Ginsco 580 pcs 2:1 Heat Shrink Tube 6 Colors 11 Sizes. $7.
If you get the shrink tubing, obviously you need a heat gun of your choice :D. I got mine on special, so $15.

Also, the Pro Micro is tiny. It's about half the length and less than half the width of a sticky note. If you're old and have bad eyes, like me, you'll really want a magnifying lens. If you don't have one, you should probably get your "Helping Hands" with one.

Couple notes:
The guide talks about the "2 & 3" spots on the Pro Micro. These are for "Clock" and "Data." If you connect it to your keyboard incorrectly, the keyboard just won't work. Just swap the wires on your keyboard.

I tested the Pro Micro every time I made any change. A couple of times, I accidentally pulled a cable from the keyboard side. Another time, I found that I put on the electrical tape too tight and that shorted a connection. Just take it slow!


31 Oct 2020, 22:38

Hi, how would you deal with the lack of grounding for this mod? I have to do an internal converter for my F XT and it just inputs random characters to the pc, someone pointed out the lack of grounding for my F XT but i don't really know how to incorporate that with this mod.


08 Feb 2021, 19:50

I just wanted to add what fixed the random characters issue for me because it might help others. I've been plagued by this problem for years (it would usually appear in the morning when I started my computer up and then eventually go away after some jiggling/unplugging), and I eventually had had enough of dealing with it and started researching a real solution.

What finally worked for me was to solder the j1 jumper on the pro micro. Afterwards I plugged my Model F in and it started working 100% flawlessly. I couldn't tell you exactly what the problem was, something to do with 3.3v vs 5v power, idk, but it worked.


09 Feb 2021, 00:24

Oh, yes

Normally all Sparkfun 5V Pro Micros ship with the J1 jumper shorted.
And all Sparkfun 3.3V Pro Micros ship with the J1 jumper not shorted.
That's not the only difference between them, also:
1) The 3.3V variant has a 8MHz crystal, while the 5V variant has a 16 MHz crystal
2) The 5v variant has an 5V voltage regulator (this is used when powering it from a battery of a higher voltage), While the 3.3V one has a 3.3V regulator which is always used.
So it's not as simple as opening up the J1 jumper to turn a 5V pro micro into a 3.3V one.
Normally in a 5V Pro Micro the J1 jumper is shorted which bypasses the regulator, and the D2 protective diode.
See full schematics here: ... o_v13b.pdf
What happens if you have a 5V Pro Micro, without J1 shorted, is that you just get a significant voltage drop from the input, through the diode, and the regulator. This is very undesireable. On one non-shorted Pro Micro I have here I'm measuring 4.62V on the output (with the input being 4.99V)
At this voltage the pro micro itself is expected to work fine most of the time, since the atmega32u4 can operate at 16MHz down to 4.5V supply voltage:
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The cheaper 5V Pro Micro clone manufacturers from ebay/aliexpress/etc pretty much all of them forget to to short the J1 jumper. And they are absolutely wrong about this. And the only reason they have not been forced to short it, is that the pro micro itself kinda works at that voltage!
However trouble comes from many directions:
1) the voltage will not always be above 4.5V. The diode to be used is not specified on Sparkfun's schematics, and someone making a Pro Micro clone could easily choose a diode with a higher forward voltage drop, and bring the voltage below 4.5V. And at that point it won't fail immediately, it will just operate out of spec, and only some devices will fail, rarely.
2) trouble comes when other stuff is being powered off of the bad voltage-dropped 5V line. The diode's forward voltage drop is current dependent, here's a typical diodes forward voltage curve:
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Also, the regulators drop-out voltage is current dependent:
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If you're drawing 500mA, which would be USB maximum, and also depending on diode selection you could drop even 1.7V total across diode and regulator, leading to an output voltage of 5V - 1.7V = 3.3V.
The atmega32u4 chip works at 3.3V but not with a 16MHz crystal, at that voltage it's only specified up to 8MHz, so it will likely fail in this condition.
Also trouble can come from whatever else you are powering not having enough voltage (i.e. your keyboard).
And also if current consumption keeps changing, then the supply voltage will vary as well!

So I hope I convinced everyone reading this, that:
You should short J1 on ALL 5V Pro Micros*

* The only exception I have heard of, is that some split keyboards, using QMK, are kinda relying on the wrongly-built ebay/aliexpress pro micros, because the way they are determining which side of the keyboard is slave, and which one is master, is by looking for the presence of voltage on the VBUS pin of the atmega32u4. And if J1 is not shorted, then only the half-keyboard that has been plugged into USB has any voltage on VBUS. If I had one of these keyboards I would try to change the firmware to not use VBUS detection, or if that is not an option, then I would mod the Pro Micros in the following way: 1) change D2 diode to a very low forward voltage schottky diode (it might already be a schottky on some Pro Micros, just not the lowest possible) 2) short RAW pin to VCC pin, so you bypass the drop on the voltage regulator.

* What I have written above only applies to Pro Micros, and ebay/aliexpress clones that are direct copies of the original Pro Micro schematic. I have not studied in detail other boards, that are promicro-inspired, or the footprint is Pro Micro -compatible. They might not even have a J1 jumper after all. Those cases should be studied independently.

User avatar

04 Mar 2021, 00:07

Here's another thing that might help.
4) When you plug in the Pro Micro, Windows should see a COM device under device manager, the exact COM port differs for everyone
Just remember the COM number.

Now, leave Device Manager open and in a place you can see it. Do steps 5 through 7. You'll see the COM port change VERY quickly. Write down that number.

Because you now know the COM port you really need, type in that long command line with that new COM port number, short the jumpers and immediately press enter. Works like a charm.


Answering the above question about grounds, the pinout on AT keyboards has a ground pin. I just attach it to one of the GND spots on the Soarer's converter. It's been working for me. YMMV. I'm not really into electronics.
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