I'm 90% done with an FTC legal custom circuit board that will interface with the Hitechnic protoboard.

My board uses a Propeller microcontroller (http://www.parallax.com) and has
- 5 analog outputs and 6 digital I/O connected directly to a Hitechnic proto-board header
- 16 analog inputs
- 10 digital input / outputs
- onboard USB FTDI (for programming the Propeller)
- 2 (independent) NXT style I2C jacks (for connecting to existing LEGO NXT Sensors, or for future use when we can connect directly to the NXT)
- header for Nordic nRF24L01 wireless transceiver (http://www.sparkfun.com) (for standalone use with wireless joysticks)
- Li-Ion battery charging through USB port (for standalone use with a battery)
- extra 250mA 3.3V power supply dedicated just for external sensors with digital On/Off control (software reset sensors)

Here's an example setup of what it can do:

Interface Theory of Operation:
Use 2 digital I/O between Hitechnic board and Propeller for handshaking
Use 4 digital I/O between Hitechnic board and Propeller to select 1 of 16 "pages" of Analog Inputs
Propeller sets the analog output for whatever "page" of data the NXT wants
The means you can have up to 5*16 = 80 channels of analog input into the NXT...Totally legal under this year's rules
If you need digital inputs too... then just use some analog set at 0 or 3.3.
If you need digital outputs too... (ie. "hey Propeller autonomous just started") then give up one or more pages of analog.

Next year hopefully we'll be able to drop the Hitechnic bottle neck and connect directly to an NXT sensor port, so we've got that covered too.

Some potential FTC legal uses:
There are 10 sets of connectors that include "3.3V Power, Digitial I/O, Analog IN, Gnd" these give you access to almost any kind of analog or digital sensor. For example to connect up to 10 Maxbotix ultrasonic sensors (http://www.maxbotix.com/). Or Panasonic I/R range sensors, or extra limit switches, or line following sensors, or potentiometers, or quadrature encoders (use 2 channels), or ...

There are 2 headers that contain "3.3V Power, 6 x Analog IN, GND" The 6 Analog are shared between the 2 headers so its easy to use some for one sensor and the rest for another.
For example connect up to this super powerful (and rather cheap) gryo/accelerometer board from Sparkfun: http://www.sparkfun.com/commerce/product_info.php?products_id=741

With this year's rules you'd still be able to connect to 2 standard NXT sensors as well.

Actually, you could connect up to 8 more hitechnic motor/servo controllers but that wouldn't be legal this year... Anybody got a use for controlling 48 hobby servos

And this is just 1 of my controllers. We can legally use 3 !!!! This truely removes all limits to what you can do on your robot. Personally, I'm not even remotely satisfied choosing which 3 sensors I'm going to connect up to the NXT. This is the ultimate sensor MUX.


The proposal:
I'm going to be having prototype boards made within a day or two. I'd be willing to get some extra bare boards if there was interest. I'd give you the BOM and you order parts (digikey, mouser, etc) and solder on the parts yourself.

If you want to buy a unit with parts on it then it'll be a month or two but I'm planning on making that available eventually too.

Let me know what you think of the idea and anybody who is interested. Of course I'll have drivers for RobotC too.

I have had many FTC teams in my area ask about exactly this kind of board.
Before I point them your way, I have a couple of questions:

- My readings of the rules suggest to me adding a battery to the board would not be legal.
Can the battery be removed? If so, does it change the overall functionality?

- Does the 250mA 3.3v power supply you mention rely on the battery? The specs for the
proto board I got limit the current from the supplies to 20mA for the 3.3v supply
and 12mA for the 5v supply.

- Do you have an anticipated cost for the board?

- You hint at the ability to program the propeller on a PC. Is this the case? Would the
boards you sell include examples?

Thanks,

marke

Chad,

Are you using SMD or the DIP version of the Prop? I have a fair bit of experience with the Prop, I have 3 protoboards and one of the education kits. I think what you are doing is a really nice way to make the Prop a legal board

If you are using non-SMD components, I think I'd be interested in the board. I already have a whole bunch of the NXT-sockets and I can just take the DIP prop from the education kit. However, my soldering skills are not sufficient enough to be fiddling with SMD components. Could you give me a price indication for the bare board?

Marke,
Programming the Prop is quite easy via the PC. You don't need an actual programmer, just a small dongle-like USB to RS232 converter called a Prop-plug. If Chad's board has this built in, then you won't even need that. There is a multitude of libraries for just about every task/purpose imaginable. The IDE for the Prop is nice and easy to use.

Regards,
Xander

After some indirect consultation with the FTC people, it seems that this board would not be legal after all. The problem is not the HTPB which is, of course, legal. However, the rules state that you can only power your board with what the HiTechnic Proto Board can supply. Unfortunately, the Prop will consume far too much power. So until they will allow the use of external power supplies, this board will not be usable for FIRST.

This is a real shame because a board like this would open many new avenues for people to explore! Being able to call on the power of an 8 core microcontroller running at 80MHz is nothing to be sneezed at!

Regards,
Xander

The folks at FTC caught wind of this discussion and asked me to make an "official" statement.

As a part of the FTC Game Design Committee, I need to remind all teams that the
ONLY source for official determination of legality of strategies, materials, etc. is the
FTC Game Manual and the Official FTC Game Q&A. If at any point there is concern about a plan, it is best to post a question to the Q&A!

And for what it is worth, I am still interested in the answers to my questions about the board. The board would also have potential uses within the FRC community. The currently FRC control system has a pair of LEGO NXT I2C connectors available for teams to plug in "sensors".

FRC also has rules about no additional batteries, but is much more tolerant about power sources!

- marke

Well I finally got the first of my boards soldered together and tested.

There's been alot of questions so I'll try to answer them all.

The board definitely works without a battery. That would not be FTC legal. It runs right off the NXT battery through the Hitechnic board.
There is a LiPo battery charger (via usb) onboard for non-FTC uses.


That's just the upper limits of the power supplies. Obviously you don't have to use that much.
Also mightor mentioned:

I disagree. I average about only 40mA between the prop and a 5 axis IMU board.

The lego documentation (and their schematics) show the 4V power supply to be limited to 160mA total. There is no physical 20mA limit per port. The HTPB just passes thru this power source with no additional limiting.

Obviously, we have to be concerned with power management, but it certainly does not prevent running in an FTC legal way.


Its almost all surface mount. Everything is hand solderable with a fine tip soldering iron, solder wick and tweezers. (that's the way I did it) Nothing smaller than 0603. There is some fine pitch MSOP parts, but its quite easily done by hand.

If you've never tried to SMD solder by hand then you probably think its harder than it is. Actually, its alot easier and faster than soldering through hole parts with the same pin count.

I did my first SMT board a few years ago with no prior experience (actually it was for an FRC competition) and the very first board worked 100%. Its very simple with the right techniques. There are many videos online showing how easy it is.


Yes, I have a FT232R built in so no programming adapter is necessary. AND I used a standard USB-B jack instead of the smaller mini-B so it has the exact same USB connection as the NXT.


Yes, all you need is a PC. The software to program them is free and the programming languages are easy.

I have the low level assembly language drivers done. These talk to the A/D and D/A converter chips onboard via SPI. This is the hardest part.

Also I have the interface code between the HTPB and propeller done. RobotC drivers for between the HTPB and NXT are done (mostly just using Migtor's driver)

I've got example code to interface with Maxbotix sonars and a 5 axis IMU with Kalman filters.

Within a day or two, I hope to have i2c code done to connect the propeller directly to the LEGO digital sensors (ie. compass)


This all depends on volume. I had my boards donated so I can't sell them (and I had 1 minor routing mistake...which is a result I'm pretty happy with)

If people can wait a few weeks we could get boards made for $15 through batchpcb.com in pretty much any quantity.
Faster lead time (5 days), are $33 each though my normal board house. I could probably order them in any quantity by shipping to a school address.

I think component costs for 2-3 boards worth ran about $75 each from Digikey. I had quite a few components already, but I think the total BOM was around that range.

For production runs...I'm really bad at predicting costs. If there's enough interest I can have a local manufacture quote the boards assembled.

If someone really really wants a board assembled and tested. I could give them a quote directly (but I probably won't advertise that price since it depends on how busy I am).



Umm, I'm very curious what "rules" the board violates.

1. its only power source is through HTPB
2. it connects directly and only to the user side of the HTPB via the digital and analog inputs.
3. no reprogramming of the HTPB is required

As far as I know these are the rules for a custom circuit and it follows all of them to the letter of the law.

The HTPB's product page says:

Unless you draw your current from somewhere else, you won't be able to run the Prop from the HTPB, you risk frying something.


That is a very nice feature of your board It'll allow people to reuse the same cable for programming.

I spoke to my financial manager (read: my wife) and it seems my robot spending budget is frozen atm. 50+ usd is a little outside of our budget right now I might have to cobble together something like it with the parts I already have (1 unused protoboard and some NXT connectors). Sorry about that

Chad, remember that the first 4 I2C packets sent to the HTPB are not guaranteed to be without an error of some kind. So send a couple of dummy I2C packets to the HTPB before doing real work. I am not sure why that is, but I've reported it a while back to Dick Swan. It only happens when using the HTPB with RobotC, not with NXT-G or NXC. I don't have an analyser to see what is going atm, but I might have access to one this coming Saturday when I go to my robotics club get-together thing.

Regards,
Xander

I still disagree with this. You keep saying "it won't work". But what I'm trying to tell you is I've been running it off the HTPB just fine. Not guessing...sitting on my desk...its physically running and nothing has caught fire (not that it would where talking about < 50mA here)

here is the quote directly from LEGO's hardware developer guide (page 6, paragraph 5)


This is the 20mA limit Hitechnic is referring too. There are no additional electronics on the HTPB that would impose an additional "downstream" limitation. Its a direct connection from the IPOWERA pin of the NXT connector to the 4V pin on the protoboard. And I'm sure the physical wires, connectors, and PCB traces could sustain several times this much current indefinitely if it needed to.

So the way I read this...the actual/real limit is 180mA total for the whole system. If I use 40+ mA in one place who really cares, not PHYSICS which is the ultimate judge of whether something will or won't work. I'll go with basic physics and electronics knowledge over what some "tech manual" writer transcribed any day.

On the other hand. If I do let the magic smoke out of anything I'll man up and admit I was wrong. I just don't think I am.

For anybody who's still worried about running off the HTPB and the NXT battery. I've done some more testing.

The Hitechnic Motor Controllers and Servo Controllers apparently draw their power off the 12V battery. I didn't want to rip mine open to check for certain (so maybe Hitechnic can confirm this) but all three controllers are only drawing .3 mA from the 4V NXT supply so I'm pretty confident.

The HTPB draws about 3mA on its own.

As mightor mentioned, the propeller has 8 x 32 bit processors internally. These are called "cogs" in propeller speak, so the current consumption really depends on how many cogs an app is using.
I ran some tests using different # of cogs. 3 cogs is probably about the fewest that an application will reasonably use.

3 cogs - 33.7mA
4 cogs - 42.3mA
5 cogs - 50.1mA
6 cogs - 58.1mA
7 cogs - 67.2mA
8 cogs - 77.1mA

which is an average of 8-10mA / cog which is matches the upper limit predictions of the propeller datasheet (pg 28).

This is the entire propeller board along with the HTPB (I'm measuring current between the NXT and the HTPB)

I've run a 90mA constant load through several batteries now with zero "frying" of the HTPB Not that I expected any.
For those interested, this load resulted in a battery voltage drop of only .037mV / sec.

I'll do a full 180mA test here pretty soon, but I expect that to be fine as well.

I also have done some testing on the accuracy of the Propeller -> NXT communications (via the HTPB of course)

This board uses a D/A converter to talk to the A/D inputs of the HTPB (which is the only legal way of talking with the NXT)

I'm getting only about 5mV of error (worse case) on this conversion process. Thats about 0.15% error over the 3.3V range or put another way somewhere between 9-10 bits of accuracy

considering the 10bit HTPB A/D converter only has 3mV accuracy to begin with, I think the board is doing very well given the current game/rule restrictions of requiring the use of the HTPB.

Hopefully, next year the GDC will allow us to connect custom circuits directly to the NXT sensor ports...its not like Hitechnic is doing anything revolutionary here.

For the cost there not even doing it very well. You could easily buy i2c chips that do the exact same thing for $2.00. add a $0.50 regulator and wire them into a NXT cable and you have a perfect HTPB replacement. I'd say Hitechnic is selling the equivalent of $5.00 worth of components for $40.00 ... a pretty good deal for them in my opinion. Also the smaller board with the header is MORE expensive than the bigger board. That header does NOT cost $10.00!!!!!

I understand to some extent the need to restrict the suppliers of the servo and motor controllers. But the GDC allows us to use pretty much any kind of custom circuit/sensor that we want (which is great) but make us go thru this HTPB board (which is silly).

Until we are truely freed from this ruling, I think this board is an excellent way to get around the limitations of the HTPB within the rules of the FTC game.

Also I really hope next year we can use the 12V power supply from the main battery to power custom circuits. I really don't understand the logic of this ruling. (Maybe those on the GDC can comment on their reasoning here) To me it seems overly restrictive for no real purpose. The 180mA from the NXT ports is too small for comfort (although its doable). We have another legal power source why not let us use it?!?

If it is 100% legal and working I might buy it.
Plus I need some codes for it, so if you could contact me ASAP and say a price for one weeks build and delivery.
My email is probably below.

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