My journey on keyboard addiction so far and Leopold FC660C Modding Question

Hello all, my name is Maiev and I am mildly addicted to keyboards.

I’ve been a lurker for a long time on this website but I finally decided to join and participate in a forum and ask questions. :slight_smile:

I’ve got my first mechanical keyboard back in 2013, then just like everyone else, I started having a hoarding problem.
I started with Full Size and TKL Razer/Corsair/Logitech then moved on to 60-65% Ducky and Kemove, and now I am currently using GMMK Pro.

I didn’t really start getting into upgrading parts until I got my first hot-swappable keyboard which was Kemove Snowfox.
After I learned about various switches, keycaps, and stabilizers, my addiction got worse.
For switches, I went from Cherry to Kailh to Gateron and ended up with my current Gazzew and Everglide switches.
For keycaps, I went from using OEM to Pudding to NPKC and ended up joining 4 separate group buys for GMK and MT3 keycaps.

That being said, my hands-on modding experience and knowledge are not as good compared to others who have been into this hobby just long or shorter than I have.
I’ve only really done lubing switches/stab, adding foam, and switching plates.
The only real soldering I’ve done was when I opened up the old Corsair K70 to swap the port to USB C so I can use a detachable cable.

Finally, here is my modding question
I just received my first Topre keyboard, FC660C White from the mechanical keyboards.
I really wanted to wait for the USB C and Bluetooth version to come out just like FC660MBT but when I reached out to Leopold, they said they didn’t have a plan for FC660C remodel yet.
So I just ended up buying the FC660C but I really want to make it USB C and Bluetooth if possible.
I’ve read that there is YDKB Bluetooth Controller that I can purchase and I also heard you can send a keyboard to the seller for a USB C upgrade.
But since it’s only offered through TaoBao and you have to ship it to China (or order from China for the Controller using Proxy), I didn’t want to go that route given the situations with shipping delays lately.

So this got me to think if I can buy FC660MBT from the mechanical keyboards to mix and match PCB/Controller/Case to make FC660C with BT and USB C.
From what I gathered so far, I believe the answer is no but I thought I would ask here.

I would also love to hear any recommendation for how I should go on about upgrading my board to have BT and USB C.
If there isn’t a solution I can do at this moment, I might end up looking to get HHKB Hybrid as an early Christmas gift to myself.

That’s all, thank you all so much for your reading and time.
I look forward to participating and learning from you all.



Welcome Maiev.

Your query re the BT module inside the 660MBT is interesting. Found these photos someone took of the internals and I’d be curious to hear the answer as well.


You can buy a YDKB Bluetooth controller here


So I know cases and board are different because of the location of dip switches on the bottom and USB port on the back.

I am sure someone who knows the board and connector better can help us out but because of difference in the main board, I don’t think it can’t be swapped.

Above is the FC660C.

Thanks for the link!
I think that was the proxy I was looking at earlier and ouch, that’s one heck of a surcharge for proxy service.

I think if I were to pay $100 for it, I might just end up getting other topre keyboard. :slight_smile:

Forgive me for not directly answering your question, but in my case I went with a Hasu controller (need my QMK/VIA fix) and a mini USB to USB C/A/x cable. You could also use a custom two part cable and swap the device end to mini for the 660c and C for your other boards. I can’t speak to Bluetooth support however.

No need to apologize!

I actually ordered 2 pack Mini USB to USB C adapter off of Amazon yesterday and currently waiting on it. :slight_smile:

Since all my keyboards are using USB C, I want to keep it consistent and want to swap from PC to Mac using Bluetooth if possible. But if it gets too complicated or expansive, I do have sets of aviator cable so it’s not too much of a hassle to swap.

I don’t know enough to read schematics and compare pins but it might be possible just to extract bluetooth module out of fc660mbt and repurpose it maybe. Just a wild guess.

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I don’t believe they would be compatible.

I believe the 660m uses a standard key matrix, while the 660c uses serial communications to several sub chips mounted on the board (just from reading the HASU firmware). Without being able to flash the stock 660c firmware to the 660m controller and keep the Bluetooth function, I want to say it won’t work. Best bet would be the ymdk controller.


Here’s the HASU pinout from the 660c folder. You’ll note there are several pins with LV4051A and LV138A, which are chips that handle the matrix scanning on the board.

Switch board Controller board Description Schematic ATmega32u4
1 20 FG FG GND
4 17 3.3V V33 3.3V/5V
5 16 5V Vcc 5V
6 15 *Z6-TP1684-4-HYS(o) FBSTB PC7
7 14 *Z6-TP1684-2-KEY(i) OUT PC6
8 13 *Z2-AD5258-5-SCL(I2C) SCL PD0(TWI)
9 12 *Z2-AD5258-4-SDA(I2C) SDA PD1(TWI)
10 11 *Z4-LV4051A-6-~EN(Col 0-7) INH_1 PB4
11 10 *Z5-LV4051A-6-~EN(Col 8-F) INH_2 PB3
12 9 +Z7-LV07A-5 (LV4051A-9-C) SEL_C PB2
13 8 +Z7-LV07A-1 (LV4051A-10-B) SEL_B PB1
14 7 +Z7-LV07A-3 (LV4051A-11-A) SEL_A PB0
15 6 +Z3-LVC138A-3-C COL4 PD6
16 5 +Z3-LVC138A-2-B COL3 PD5
17 4 +Z3-LVC138A-1-A COL2 PD4
18 3 +Z3-LVC138A-4-~G2A Z6-TP1684-5-~EN COL1 PD7
19 2 +Z7-LV07A-11-~InsertLED LED1 PB5
20 1 +Z7-LV07A-13-~CapsLED LED2 PB6

I’d have to review the nice!nano pinout and ensure you have enough IO, but you might be able to take the HASU fc660c firmware, add map it to ZMK, and run it on a nice. I’ve never tried to bridge that gap, but as long as the IO is there, I don’t see you couldn’t.

Edit: The HASU controller uses an ATmega32u4, same as a promicro. The Nice!Nano is a drop-in replacement for the promicro, and has 23ish IO points. Seems to me that it would pretty straight forward to map the IO to the corresponding pins on the Nice and use the HASU firmware as a roadmap.

I have a nice! laying around, might have to give it a shot

After inquiring at ZMK, it sounds like the firmware would need to be developed independently to be within license, perhaps. Might still give me something to do with my nano.


Wow, that’s like whole lot above my understanding and skill level. :slight_smile:
Thank you for the informative writing and information.

I will be on the look out for your next amazing post like the one you did for the RGB in FC660C.

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I absolutely was not trying to overdo it with technical data. If you have any questions or need clarification at all, please do speak up, I’m happy to try to clarify. :grinning_face_with_smiling_eyes:

Oh, you are too kind!
I am just not as experienced in hardware as I am in software.
You explained everything really well. :slight_smile: