Re: Anyone interested in a FTC legal Custom Circuit Board?
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.
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.