Using FET transistors as switches

When over a year ago I published this post about using transistors as switches, I described only how to do it with bipolar transistors. And bipolar (NPN and PNP) transistors have a small problem: they are current driven, so they consume current when they are switched on. They consume much less than they drive, but still…

Field Effect Transistors (FET), and especially the ones from MOSFET family, work in a slightly different way. Instead being current driven, they are voltage driven. Than means, to conduct between Source and Drain terminals, specific voltage has to be applied to Gate terminal. More than that, FET transistor consumes current only during switching. It works kind of like a capacitor. When Gate is charged, it stops conducting electricity.

And that, in case of low voltages and low currents (3.3V – 5V logic level and few hundred miliamps), removes the requirement of Gate resistor. Small MOSFETs like 2N7000, BS250 and other, can be directly connected to microcontroller outputs. Cool!

Switch with N-channel MOSFET

N-channel MOSFET is ON when positive voltage (comparing to Source) is applied to Gate. So, Load will be powered when HIGH state is applied.

N-channel MOSFET as switch

Switch with P-channel MOSFET

P-channel MOSFET is ON when negative voltage (comparing to Source) is applied to Gate. So, Load will be powered when LOW state is applied. It acts like an inverter.

N-channel MOSFET as switch

Gate resistor

In case of bigger currents and voltages, gate resistor might be required since FET gate acts like a capacitor and passes electricity until charged. Consult transistor data sheet.

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Scarab Knife 200 finally in the air

It took me much more time to put my Scarab Knife 200 4″ from into the air and actually fly it. First try that happened 2 weeks ago failed due to beginner mistake: too long motor screw caused one of the motors to overheat. I had to order shorter M2 screws and redo some other things: add 1000uF 36V low-ESR capacitor to power rail, relocate VTX and X4RSB RX. Nothing super fancy. Final effect looks like this:

Scarab Knife 200 racing quad

Scarab Knife 200 racing quad

Scarab Knife 200 racing quad

There are a few problems that I hope proper tuning will solve. One of them, is strange wobble, or low frequency oscillation, on full throttle. I’m not sure what is the source of it. It might be from quite soft props. I will try replacing stock HQProp 4×4.5″ with DAL T4045. But second problem is that probably 4″ props do not match my flying style. Those small props just do not gip so much air as 5-inchers and do not keep flying path as good as I’m used to. I had similar feelings when testing JJPro P175, so that might be the case.

Next tries in 2 weeks…

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AnyFC F7 Pinout

There is still very little about AnyFC F7 on the internet. Especially pinout is kept secret. Without sambas official GitHub repository for hardware projects, there would be nothing at all. I’ve decided to close that gap a little and prepared full pinout for AnyFCF7.

AnyFC F7 Pinout - Top Side

AnyFC F7 Pinout - Bottom Side

Yes, I know they are hand drawn and scanned, but I have a strong aversion for computer graphics software. I can move a slider left and right, but every time I have to do some creative photoshopping, my head starts to hurt. This is extremely ironic, since my major at university was computer graphics. Heh…

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FrSky SmartPort Telemetry on AnyFC F7

STM32F7 CPU family present in newest, experimental, flight controllers like AnyFC F7 (as well as upcoming AnyFC M7 with smaller STM32F722) simplifies many things. For example, comparing to F4 boards, SmartPort or S.Bus connection is extremely simple and can be done on any free UART. No more hardware hacks, external inverters and other “special” ways of doing things.

It’s super simple again, and here is how to do it in Betaflight (Cleanflight 2.x) and INAV


The only required hardware is a cable to connect SmartPort enabled receiver with free UART port on F7 board. This will work on X8R, X6R, X4R, X4RSB, XSR and any other. The trick is to connect S.Port pin with UART TX pin only.

How to connect F7 flight controller to SmartPort

Continue reading “FrSky SmartPort Telemetry on AnyFC F7” »

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Marabou Stork reborn

It took me quite some time, but I've finally rebuilt my Depron FPV airplane Marabout Stork after last year's crash.

In theory, all I had to do, was to replace nose section. At the end, it turned out, that I should also reinforce wing mount, redo FPV system and replace flight controller. So, full list of changes:

  • Rebuilt nose section that is longer than original by 30mm
  • Full sized MinimOSD was replaced with Micro MinimOSD to save some space
  • Flip32 flight controller was replaced by SP Racing F3 and external BMP280 barometer
  • INAV 1.7 baby!
  • Various reinforcements, mainly around wing mount

Weather conditions in above video were far from perfect. Wind speed around 50km/h made everything hard.

It still awaits for new GPS module, since Ublox Neo-6M is really, really, really crappy solution…

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Hands on: AnyFC F7 from Banggood

Before we proceed, short clarification. Legal background of AnyFC F7 flight controller from Banggood is iffy. It’s not that BG ripped the design from Sami Korhonen (sambas). Sambas published design of his AnyFC under Creative Commons BY-SA. So, it’s free to copy this design as long as Sambas is referenced as author, and license is not changed. The problem is that “by attribution” part is not met. Sambas is not referenced as author on BG. Still, Sami wrote that he is fine with it, as long as boards quality is good enough.

Today I have something brand new to write about. Probably the first commercially available flight controller based on STM32F7 CPU: AnyFC F7 from Banggood.

AnyFC F7 STM32F745 flight controller

Continue reading “Hands on: AnyFC F7 from Banggood” »

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DIY brushless motor kit – I give up, for now…

Latest update on the topic of DIY motor kit from Banggood (DIY Assemble 2204 2-3S Brushless Motor 0.42*2.8 Copper Wire with Motor Cap Banana Plug): I give up. For now, at least.

In total, I tried to wind this motor 6 times. In every single case it ended in the same way: one of the phases burned. So, it's either me, or this kit. I've verified winding directions and termination schema for at least few times, and if I didn't missed something extremely obvious, I did it in a right way. I even verified winding directions during "unwinding". So I start to suspect, that this motor is either no 12N14P DLRK (not very probable), or it should not be winded with 0.42mm wire. Next week I will order 0.20mm wire and try one more time…

This is a winding schema I used:

dlrk winding schema

Poles goes as follows: AabBCcaABbcC where capital letter is clockwise, while small letter is counter-clockwise.

Phases were connected like this:

  1. A1-C2
  2. B1-C1
  3. A2-B2

Sure, I could have done something wrong. But not 6 times in a row…

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GPS Racer: worklog #4

Yesterday I finally maidened my GPS Racer in full FPV configuration. RunCam Owl Plus and VTX finally arrived, it was not raining, so I took recording gear after sunset and went flying.

To be precise, it was not "night". But it was pretty dark. Too dark for my RunCam Swift. Owl Plus was sensitive enough to fly. It was not perfect, but doable. Next step: not IR blocked lens and IR emitter for real night flying. Both have been ordered.

Plus, thanks to GPS and OSD I finally saw the speed this thing can do. 92km/h recorded, but that was not the limit on those 6030 props. I do not think I've opened throttle to max…

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DIY brushless motor kit – first failure

Just like it was expected, my first attempt to wind a brushless motor (12N14P) was a failure. Probable cause: short circuit between phases and my creation released magic smoke.

Then I tried for a second time, and failed again. This time less, no smoke, but motor overheats and does not want to start most of the time. I suspect this can be an ESC problem (Emax 30A) that is configured for DampedLight. Perhaps motor is rotation too fast (no load after all) and ESC tries to slow it down. Hard to tell. Tomorrow I will add a propeller and disable DampedLight. Maybe it will help. I will also try WYE configuration. Right now phases are connected in Delta setup.

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