ESC circuit design questions with simonk firmware on Atmega8 - RC Groups
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Jun 10, 2013, 07:07 AM
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ESC circuit design questions with simonk firmware on Atmega8

Hey all,

I am throwing together a ESC design on a board that will integrate into a quad frame better. The design is based on the Blueseries HK/Mystery boards which a (partially accurate) schematic is found here:

I have 4 main questions:
1) D1 which is connected to pin 24 - does anyone know what this is? Just a regular diode, zener? Based on a few other designs it seems like it might be a zener used for VREF but there aren't any on the HK boards. Anyone know if this part is necessary or have a hint where to find a part for it?

2) The voltage divider on pin 25 (R20, R21 and C7) looks like it's used for the low voltage cutoff on the battery which the simonk firmware gets rid of - does anyone know if this is true and if I can leave these parts off?

3) Back emf filtering capacitors - (C10-C12), I read that these should be removed when flashing a Blueseries board for better response so I am planning on leaving them out. Is this true?

4) The filtering capacitor C8 on the SIGNAL_IN line, anyone know this value? What is the max PWM or PPM frequency on the SIGNAL_IN line? Then I can calculate this myself.

Thanks a bunch, if you have any info that would be awesome. Also, once I get a decent design working this will all be open source
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Jun 10, 2013, 07:48 AM
An itch?. Scratch build.
eflightray's Avatar
I would recommend asking the moderators to move your thread to the --

RCGroups DIY Electronics forum

(If you click on 'Report', top right of your post, there is an option there to ask for it to be moved).

Although you may get the answers here in the Power Systems forum, they are more likely to be interested in expanding on your thread, plus they may even have something similar in their forum.

Plus Welcome to RCGroups, I hope you have success with the project.
Jun 10, 2013, 06:24 PM
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Sorry about that, thanks for the tip!
Jun 11, 2013, 11:18 AM
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So from more and more reading it looks that D1 is used for temperature monitoring and overtemp protection which is not used in simonk firmware so I plan to leave pin 24 floating in this prototype and hope it works.

I'm also learning a lot more about the FET stages and may redesign later to increase efficiency but for now I think I have a PCB ready to send to fab
Jun 11, 2013, 11:43 AM
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I have been researching something similar for the past couple of days (integrating an ESC into a multi-wii board). Do you have the files that this schematic is from? Would you be willing to post them?
Jun 12, 2013, 05:30 AM
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I'm not sure what files you mean, all I have is the schematic above which I got from here:

There are some resistor values that are not correct on the one I posted above and I am not sure on the others in that link. Other than reading about simonk's firmware and learning BLDC control theory, that's really all I have been going off of.

Once I have something verified working I will gladly share my PCB layout files but I have to order boards for prototyping which takes a while.
Jun 12, 2013, 06:01 AM
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This schematic should not use , because FET very hot , you should use ir2101 with shematic mystery 40a
Jun 12, 2013, 07:42 AM
Supersonic Engineering
GordonTarling's Avatar
Nuts - rather than leaving an unused pin just floating, better to tie it to Vcc or ground via a resistor - more predictable that way.
Jun 14, 2013, 06:59 AM
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As the AtMega8 has built-in pull-up resistors, it is perfectly acceptable to leave the pins unconnected and enable the pull-up. Then no external resistor is required. That also has the small safety advantage that, should the pin ever be incorrectly programmed as an output, it will not short to one of the power rails.

Martin Jay McKe
Jul 13, 2013, 02:40 AM
Registered User
Well with a ton of help from Simon, I put together a layout, ordered parts and PCBs and it works!

I re-assigned a lot of the pins on the ATmega for an easier 2-layer layout so with some help, I made a new .inc file and Simon sent me the compiled hex file.

Hopefully this weekend I will be able to upload my eagle schematic.

I'm in the process of another layout now to fit my quad build better.

To answer a few of my own questions in the OP:
1.) The symbol on the schematic is actually meant to be a thermistor - I left this part out and did not define a temperature pin in the .inc file because it's not necessary.

2.) The voltage divider is meant for the low voltage cut-off. I also left these parts off and assignments out of the .inc file because there is no low voltage shut-down. Instead I tied the pin high per Simon's recommendation.

3.) The back EMF filter capacitors on the sense lines should be removed. Simon also recommended different resistor values be used for a better signal.

4.) I used the ICP input on the ATmega for the speed signal because it has internal filtering already. Simon did recommend putting a large resistor to ground here. I will get the schematics up soon with all the values.

fantasy1988 - I didn't want to use FET drivers here because I only need a 20A design for now. In the future I would like to make a 40A design for 6S battery which will definitely require drivers.
Jul 14, 2013, 05:51 AM
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MGeo's Avatar
Great progress! Did this mean you used the schematic of post #1? If not, could you post an export of your schematic?

Jul 17, 2013, 08:57 AM
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Yes - the schematic from the first post is pretty similar to what I used, here is my Eagle schematic - sorry I haven't had time to clean it up but all the values are parts should be on there.

If you have any questions about the design I should be able to help. The firmware that's loaded onto the chip is also in the folder below. Also available supported here:

Also here are the Eagle schematic and board files. The board needs a lot of adjustments - mainly the holes for power and motor outputs are too small. The FETs can also be placed a lot closer together. I'm also learning to use polygon's better so forgive me on the mess - it was easiest at the time to make paths I could add solder to for extra current capacity.
Apr 10, 2014, 02:36 AM
Registered User
Hy!i want to make something similar but with a DIP version of Atmega8.i will design the hardware but i'm fool at programing...All the .inc files use the ADC6 and ADC7ports of atmega...
I want to design using Nfets,ir2101 drivers and DIP version of atmega 8.Can somwone suport me with an modificated compiled hex?thx!
Last edited by mihun70; Apr 10, 2014 at 10:34 AM.

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