Encoder with built-in transmitter module

Any old or new electronic projects on the go
Martin
Posts: 744
Joined: 16 Feb 2018, 14:11
Location: Warwickshire

Encoder with built-in transmitter module

Post by Martin »

I'm thinking of designing a board that would give us a compact, cheap, encoder board, with a built-in RF module that will bind to standard full-range receivers. It should work out cheaper than our standard route of buying a Nano plus a separate encoder module, as well as being simpler to wire up, and occupying a bit less space. I thought I'd start a thread where we can discuss the best options, possible pitfalls, etc., before I take it any further.

The basic idea is to make something that combines the best features of the DIY-more board and the RF-Nano, but using the high-power CC2500 module in place of the nRF24L01+ Then we can bind to the FrSky receivers (and the newer equivalent-but-cheaper RadioMaster receivers).

So my ideas, so far, are:
  • ATmega328 based - so we can program it just like an Arduino Nano
  • 3-pin connectors (GND, +VE, Signal) for the I/O pins we want to connect easily to pots, switches, LEDs, meters, ...
  • Switching regulator, for lowest-battery drain
  • Boost/Buck converter for reliable operation from a single Li-ION battery, or any battery voltage up to 12.6V
  • ICSP connector for easy connection of (3.3V) USBasp
  • ... or built-in level shifter for safe operation with any USBasp?
  • ... or a built-in 3.3V USBasp with an on-board USB connector for programming?
  • Two versions of the board (if people want them):
  • ...one with larger through-hole components/chips for people who want an easy DIY-kit build
  • ...a smaller, cheaper one with surface mount components - nowadays JLCPCB will assemble the (surface mount) stuff for us, at a reasonable price - so we'd only have to solder in the pin connectors etc, ourselves.
  • We could supply the boards / chips, ready-programmed with one of Phil's encoder sketches, for those who just want to build transmitters and don't want to mess about with programming. But of course, it will be easy for people to download and flash alternative sketches, modify the sketches, or create their own programs.
Suggestions please. If we decide to go ahead, who might be interested in buying such boards? How many would we likely have to make?
Would any of you like to volunteer to help with the design, build, programming, documentation, stocking, selling, and/or customer support?
User avatar
Wayne_H
Posts: 809
Joined: 17 Feb 2018, 05:26
Location: Temora, NSW. Australia
Contact:

Re: Encoder with built-in transmitter module

Post by Wayne_H »

Wow Martin, quite a task you have in mind :shock: BUT, I'm in, of course ;) :D

Put me down for 5 boards to start with.

To answer some of your questions:
Other features?? -
  • built in buzzer for audible alerts, preferably on Phil's normal (default?) output pin
  • OLED display driver for tx meter. This probably needs another arduino - if so, then shall leave it to you boffins as to the best way to incorporate this (or not).
  • Is stackable expansion boards a viable option? E.g. for meter and/or display driver
  • simple model memories, such as in your super S/C Tx
  • interface for a simple programing & model selection module with display. That way, the "simple" external appearance of our converted tx's is preserverd while keeping full functionality
  • buddy box capability
  • automatic self destruct function should our Chinese friends shamelessly try to ripoff your hard work (only partially kidding :P )
Would any of you like to volunteer to help with the design, build, programming, documentation, stocking, selling, and/or customer support?

Even though I'm on the wrong side of the globe, I'd Love to!
I can assist/contribute/participate with all of the above, but "design" for me would be about physical configuration, not software writing.

I've not assembled surface mounted boards yet, but I have successfully repaired a few and I can use an oven and follow instructions!! :lol:
Even went to the optomitrist today & had my reading glasses prescription updated!!
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
Martin
Posts: 744
Joined: 16 Feb 2018, 14:11
Location: Warwickshire

Re: Encoder with built-in transmitter module

Post by Martin »

Great suggestions Wayne! :)

I don't think we should try to do any surface mount assembly (except perhaps for the initial prototypes) - far easier to get one of the Chinese board producers to do it for us - they offer this service now at very reasonable cost even for fairly low-number build runs.
Wayne_H wrote: 09 Dec 2020, 12:54
  • automatic self destruct function should our Chinese friends shamelessly try to rip off your hard work (only partially kidding :P )
Really, I don't think we should be adverse to this. If there's a big enough market, and our Chinese friends decide to make and sell clones cheaper than we can, then it will save us the hassle of building / testing / shipping them. :D I don't expect to make any money on these things. :lol:

...But there's a very long way to go before that could ever happen - first we have to make a successful design and sell enough of them to attract the interest of any potential clone-makers.

Any comments concerning regulations and certification? Our board will be using standard CC2500 RF modules, so it should be just as safe and compliant as any other module that uses them - and there are loads of those on sale everywhere. Is this something we should worry about?
Tobe
Posts: 665
Joined: 16 Feb 2018, 06:19
Location: Varberg or Stockholm, Sweden

Re: Encoder with built-in transmitter module

Post by Tobe »

If you are looking at CE compliance there is a distinction between when a product is considered commercial or the result from a recreational activity.
In a commercial product also if the RF module is CE per se it would require that the assembly in which it's included is also CE and the producer of the RF module might have to approve your usage of their RF CE module.
When your assembly is the result of a recreational activity it's enough that the RF module is CE and you as a person will be responsible and liable for the context it's included in...this also limits the usage for your own personal usage and if you sell the assembly to a 3rd part you will remain liable and responsible like it's in regular product producer liability.
To the best of my knowledge it works about the same in the US with FCC
Basically we have to follow the same rules that applies to a Ham when he/she builds its own radio equipment but as we are on an open Frequency we don't need to be licensed. Theoretically you could build your own 2,4 GHz transmitter from scratch and don't need CE on the RF module but as soon the module is bought "built up and running" it needs CE
.
Cheers,

Tobe
Martin
Posts: 744
Joined: 16 Feb 2018, 14:11
Location: Warwickshire

Re: Encoder with built-in transmitter module

Post by Martin »

Thanks Tobe.

We'll only be selling a "component" or "partial kit" - not a complete transmitter. The customer will have to supply his own case / stick units / switches / battery / etc.

And we'll be doing it not for profit for the benefit of home constructor enthusiasts.

In your opinion, would that make us compliant with the regulations?

What if the customer had to take the final step of soldering the CC2500 module in place on our 'motherboard'? Does it affect compliance if the
customer has to purchase his own CC2500 module separately from a different supplier, or could we supply one as part of the "kit"?
Tobe
Posts: 665
Joined: 16 Feb 2018, 06:19
Location: Varberg or Stockholm, Sweden

Re: Encoder with built-in transmitter module

Post by Tobe »

If it's a partial kit and the "buyer" has to perform at least 51% it's normally considered OK... it's the same concerning kit cars & homebuilt airplanes etc. It doesn't matter what kind of organization supplies it unfortunately, also a no profit or pro bono can be considered commercial if payed...in some occasions payment for an item or service is replaced by a suggested donation!
I would guess that the main board would have to be seen as any Arduino board with a shield out there and as RF modules are readily available so if everything else has to be done by 3rd part I don't see any issue or problem.
The key point is how it's presented and the stated usage.
The 3rd part must be encourage to check and apply the rules in the country he lives, I know for example that in Japan and Singapore a project like is on the edge of what is allowed.
Cheers,

Tobe
JohnH
Posts: 30
Joined: 18 Jun 2019, 03:48
Location: Eden, MD USA

Re: Encoder with built-in transmitter module

Post by JohnH »

Hi Martin,

I like the concept, and I would purchase at least 5 modules. I also like Wayne's suggestion of a programming interface to adapt the unit to different types of transmitters that either used a display to use for programming, or switches and Pots to program, servo centering, servo travel limits, dual rates, exponential rates, universal mixing, etc. How many channels are you considering? To match most transmitters, I would suggest at least 7 or 8.
Thank you very much. I cannot offer much technical help, but I am excited at the prospect of having such a module available.

John Haffner
John H.
"Here's another fine mess you've gotten me into."
Martin
Posts: 744
Joined: 16 Feb 2018, 14:11
Location: Warwickshire

Re: Encoder with built-in transmitter module

Post by Martin »

Responding to the questions/suggestions so far:

Thanks for your help Tobe - it sounds like we should be able to sell a kit, maybe even with a ready-soldered-in module, without fear of jail time, except perhaps to Japan/Singapore and similar countries. :lol:

Built-in buzzer? Yes, we should do this.

Model memories? Possible. Only real problem is using up all the I/O pins with buttons for the selection. For those using a display, we can do a 'scroller wheel/roller' including 'press to select' using three input pins. For people who don't want a display, those three pins, and the two 'display' pins could be some sort of 'mode select' switches/jumpers - allowing up to thirty-two different set-up choices - but how would you configure the model memories without a display? There's also the possibility of using the main control sticks for selection/navigation with or without a display - but we'll need to think of a safe way to implement it that can't affect the transmitter when you're flying, and is reasonably intuitive for the users.

OLED display driver? Yes (optional). Providing it's just to display battery voltage, flight timer, and SIMPLE text-only displays, I think we can do it on the same chip. If you want fancy graphics then yes, a second Arduino would be necessary. There's also the problem of the OLED displays we use being perhaps a bit too small, and not visible in bright sunlight - but I've yet to find a cheap, readily available, alternative display. The two or four row, character-only, LCD displays, like I used on my single channel set, are readable in sunlight, but perhaps a bit too large, and old-fashioned for most?

Separate display/control module, that can be normally left disconnected? Yes good idea. We just need to program it so that the display/controls can be disconnected without upsetting the operation - then the same program can be used for both the 'built-in' display option, or the pluggable module version, or for those who don't want either. The connecting lead can't be too long, but people wouldn't want it much longer than a foot or two anyway.

Stackable expansion boards? Yes, if and when necessary. But I think we should concentrate on getting the 'base board' working first - I think most users will probably not want expansion.

How many channels? The ATMega chip has eight available analogue inputs, but if we want to drive an I2C display, that uses up two of the 'normally analog' pins. A battery monitor also uses an analog pin. So probably best to settle on 5 analog inputs for sticks/pots/sliders with a further 3 channels operated by switches - these could be two or three position switches, depending on how many digital pins we use for other functions. (If people are interested in the through-hole, easy to solder, chip version, that has two analog pins missing - perhaps we should forget about that option - at least to begin with?) Separate analog trim pots aren't feasible, but we already know how to wire trim pots to combine with the main 'stick' channels. There aren't enough direct digital inputs for digital trim buttons (but see below).

Buddy box? Do you want the transmitter to be the master or slave, or selectable? It uses up at least one extra I/O pin - two for master mode.

We need four pins to drive the module, one for the buzzer, perhaps one or two for buddy box? The ATmega chip has fourteen digital I/O, so with the extra channel switches, and other user controls, we're already close to using them up. Maybe we should consider some on-board I/O expansion to provide extra digital input and/or output pins? An alternative would be to use a different chip to the ATmega328 with more I/O built in - but I think that would frighten off many potential users who are comfortable with Arduino UNOs and NANOs. Thoughts?
User avatar
Kad370
Posts: 9
Joined: 19 Sep 2019, 11:28

Re: Encoder with built-in transmitter module

Post by Kad370 »

Just finishing my single channel transmitter.
At first I was thinking same as you, to strip down nano and use just processor and few components arround it. But nano is still small and with external module you get many options. Building multi protocole module is not so easy job to do, also not that cheap.
I’m thinking to share all my files, when finish my tx. Friend of mine also modified arduino code, so now it works with 128x32 oled. It is very small oled, so it could be hidden if someone wants clean tx without modern “tehnology”.
309669F8-B7EA-4634-9403-60AE70AA05DA.jpg
A1F722EB-6603-4D08-81F2-AF579DEA6C6F.jpg
User avatar
Wayne_H
Posts: 809
Joined: 17 Feb 2018, 05:26
Location: Temora, NSW. Australia
Contact:

Re: Encoder with built-in transmitter module

Post by Wayne_H »

Hi Martin,

No pressure intended or implied - just curious as to what "developments" may have happened with this project?

Certainly, rereading the thread (yet again) & looking objectively with the clarity of 20:20 hindsight, I for one went in hard with my suggestions, when sound basic functionality was probably what you were after, I think?? :shock:

Anyway, I'm still keen to help/contribute in whatever way I can.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
Post Reply