SirMixALot DYI F7 Fully Loaded Flight Controller

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Joined: Wed Jun 26, 2019 3:30 am

Wed Jun 26, 2019 4:01 am

Hello, I am experimenting making my own FC. I used the CL F7 plus some minor tweaks. Some questions:

1) Do people typically power anything off of the USB besides the FC MCU and Receiver? Amps are limited to 500mA (USB 2.0), so that seems safe/reasonable and consistent with other FC's.

2) Is there a way to drive the MAX7456 chip from the MCU's timer? Seems like there are plenty of available that could do 27MHz.

3) Is the inline Cap and Resistor on VOUT of the MAX 7456 really needed? The documents say something about connecting it to coax, so wondering if any of that can be removed when connecting to another IC, like a vtx?

4) General EE question: when you have ICs next to each other that have decoupling caps specified for various inputs, do you really need caps for every single IC/pin, or can one serve dual purpose?

5) What does USB_CONNECT pin do in BetaFlight?

6) See anything egregiously wrong with this schematic?
F722 Flight Controller.jpg
Last edited by jrowe88 on Mon Sep 02, 2019 4:42 am, edited 1 time in total.
Posts: 17
Joined: Wed Jun 26, 2019 3:30 am

Wed Jul 03, 2019 5:48 pm

Well, I had some spare time on my hands and started building this out. If anyone is interested in a prototype for cost, let me know. I am trying to get the BOM cost down and will make a few more than I will ever need.

F722 Processor
ICM20602 Gyro
USB-C connector
More robust JST-GH connector
Onboard WS2812 LED0
3 Amp 5V BEC
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Joined: Mon Apr 15, 2019 9:03 am
Location: Perth

Thu Jul 04, 2019 4:32 am

1. No, you should be fine. With pulling power from USB.

2. I don't think that can work due to some limitations within the betaflight. I could be wrong though. For reliability and just a known working circut, I would continue to use the setup you have now

3. Yes, it is needed and put it as close to the chip as possible. But you can reduce the size of the caps a little bit from other boards I have seen that have gotten away with it just fine.

4. I'm not sure, lol

5. Used to detect when a USB is plugged in rather than power from a vbat or something. It's because betaflight changes stuff when USB is plugged in to prevent arming and stuff.

6. Looks pretty dam good. Well done. I would check the USB circuit again for the diode so it only powers the fc from one and not vbat when plugged in or something. I might blind and missed it but not sure if it looked right. Love the idea of a type c plug I just changed it on mine
Posts: 17
Joined: Wed Jun 26, 2019 3:30 am

Fri Jul 05, 2019 2:26 am

Thanks, @TonyFPV. I think the USB is OK. I am using a dual supply mux chip (TPS2115A) that acts as a diode, plus a lot more for smooth switching, no back/cross-supply, etc...
Posts: 17
Joined: Wed Jun 26, 2019 3:30 am

Tue Jul 09, 2019 3:37 am

Ok...a few more hours this weekend. Found a few bugs and added compass connections. About ready to make the first test board!
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Joined: Wed Jul 10, 2019 1:47 pm

Wed Jul 10, 2019 1:55 pm

I am new to all of this... I do have some electrical background though. In terms of firmware how do you know which one to flash? I know that for the f4 board project the "furyf4" firmware was compatible. If I wanted to make an f7 board which firmware would I use? Does it depend on the chip? Does it depend on other components as well like the gyro(dual gyro) and osd? Can I make/modify firmware? If someone could explain this to me or point me in the right direction for more information that would be great! Send links if you have anything useful!
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Joined: Wed Jun 26, 2019 3:30 am

Wed Jul 10, 2019 11:13 pm

Hi @scheckdog, as far as I can tell, classically (for BetaFlight anyway), you would either need to design to have your pins match an existing firmware (e.g., Lumenier F7 and Matek F7SE use the same firmware), or you would do a pull request and get the developers to add you. If you look around in GitHub you will find the ".h" files that list the pin mappings per supported board. As of the newer 4.X versions of BetaFlight they use something called "Unified Targets" which are designed to make it easier for what we are doing it. There is basic unified firmware that then loads a "config" file to set the pins. The config file is a pretty self explanatory setting of the pin assigments (and any other BF config you would enter from the CLI). I believe this make it easy to flash a chip with sensible default and as little config as possible needed by the user (e.g., you can assign UARTs to their expected function, choose the gyro, etc). You can also find the .config files in github. Lastly, there are instructions explaining this here: ...

It appears for a little while vendors will be needing to support both the .h files to have their build system automatically build your custom firmware as well as a .config file.

I am about to go down this path, so I'll let you all know how it works....
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Joined: Fri Jul 12, 2019 4:03 pm

Fri Jul 12, 2019 4:15 pm

Very nice job on the FC! It has every feature that I am looking for. I would like to build one of these. Can you share your kicad files? I would like to try to make a FC in 20 x 20 mm form factor for toothpicks. Also want to do an esc. Im sick and tired of crappy chinese hardware. I want to build high quality electronics. I have been into SDIY for many years and have lots of experience designing boards and schematics. I would love to help this project develop. I am looking forward to your progress.
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Joined: Wed Jun 26, 2019 3:30 am

Sun Jul 21, 2019 1:37 pm

Back from the FAB--all looks good! Was psyched to build the first article, but on laying out parts found an error: I somehow got the wrong foot print -- 2x2mm instead of 3x3mm for the source select IC. Doh! Will probably solder up the power controls and jump over that to make sure the Battery -> 5V -> 3.3V all works nice and clean.
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Joined: Sun Dec 23, 2018 9:51 am

Wed Aug 14, 2019 6:12 pm

I was wondering if you have any updates on this project?
And are you using a brand new chip, or you'll solder off an already programmed chip from another flight controller?
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