Re: Battery powered raspberry pi
 

If a transistor, zener diode and some resistors (which is a very simple linear regulator) can be offset effectively by thousands of transistors in an advanced piece of silicon semiconductor < are you sure that's the best trade because the second you need a PCB you'll be designing it anyway.

Within reason sure.

Well realistically every PC on the planet is interrupt based. So since your first computer has interrupts that leaves room from some that don't. :p

You can always practice interrupts on the PC you used to program the Parallax Propeller.

No these generalities are not necessarily correct.
The FPGA has the advantage of the gates being close together.
Therefore even if you use the highest speed CMOS/TTL individual logic you can get the FPGA has the gates closer together.
You have more flexibility with ICs instead of the FPGA for example you can get ECL instead of TTL where you want it.

The scientific method and experience will tell you the best choice for the criteria of any solution at a point in time (which impacts what technology is available since you don't make your own semiconductors).

Don't make mistakes - less to clean up!
Start off with PCBs you draw with a Sharpie and etch yourself.
There's a kit at RadioShack, ask for it, they usually have it in the back.

You make compromises to use a 3D printer like that.
You make compromises all the time the key to expertise is to recognize them.

I typed enough without multiplexor and demultiplexor. :yikes:

You make a routine to initialize and don't worry about performance.
You optimize a routine to fetch the data using one or more cogs if you need to (hint > the hub switch is sequential so you can read the same input from cog 1 as you can from cog4 < exploit that to reduce the timing and impact of the hub switch timing).
From within the fetching cog(s) find the min/max/average and store the current.
Use another cog(s) to grab the min/max/average and current reading from the hub shared memory (remember within a cog is faster than in the hub shared memory).

You probably want to use a running average to reduce noise so you probably want a way to start/stop/restart that average based on flags stored in the hub shared memory.

You will quickly discover that autorouters are not the be all and end all of PCB design. An autorouter does not understand the currents in a circuit and usually it can't model the RF characteristics of a circuit. That being said I'd hate to try to layout a 6 layer board with 1,000+ parts by hand.

Look at Altrium, FIRST used to get you a license for FRC reasons.
http://www.altium.com/en/first-robotics-competition

It is powerful professional software designed to do this job.

That's a bad idea because it will have to be a very long copper trace. Use a resistor to bleed a load.
Otherwise you are trying to make a PCB with a characteristic that is otherwise undesirable.

There are finite limits to transformers on PCBs and I strongly suggest you buy the part if you lack the experience to understand the mathematics involved.

The PICs are Harvard architecture RISC processors. So yes high clock frequency but generally simple instructions means more instructions to do something that a CISC CPU can do in one but maybe slower.

So maybe a simple problem can run in one instruction at 4 clock cycles at 25MHz on a CISC CPU.
That same problem can run at 10 instructions at 1 clock cycle each at 50MHz on a RISC CPU.
Think it over.

Here, this is worth lots of my typing:
http://eecs.wsu.edu/~aofallon/ee234/...reOverview.pdf

There are a few different versions of ISP/ICSP. The process differs between them. Unless you know which chips you are targeting buy the cheap unit so you know it should work. Building something yourself usually works but it can create limitations like being able to program the programmable feature registers.

1. As a student >with supervision< I encourage you to get the RadioShack kit and learn how to make a PCB with a marker.
2. Then with iron on transparency film you can get from eBay or Mouser using a laser printer or photocopier.
3. Then send Gerbers and NC drill files out to a board shop.
4. Then send assembly drawings to an assembly shop.

You can also solder mask yourself but then you need to get more involved.
You can etch and Liquid Tin a board with hobby tools easily.
Please be aware the etchant is an acid and should be treated with respect.

Your Pi is alive? Does it make more Pi?

Low frame rate is often adequate enough for a lot of tasks.


Now....for something directly on topic:

How many teams need/want a COTS enclosure with a battery powered computing device in it and which one?

Re: Battery powered raspberry pi
 

Ah, out of respect for your incredibly long trail of informative posts, I am very reticent to try to bring this up, but it is apparent that you are intimately familiar with the classic 8 & 16 bit PIC's, but have not explored the 32bit based products very deeply. Start here for some interesting new products released over the last few years http://www.microchip.com/pagehandler/en-us/family/32bit . Also, there is data about that shows that Microchip products are leaders in memory efficiency in 8, 16 and 32 word sizes.

Plus, stuff like this make for a new world http://www.microchip.com/pagehandler...makes-sen.html I'm trying to figure out how I can plop it (and the associated sensor suite) on a robot.

On another front, I am amused at the argument resurfacing between CISC and RISC, as the technology sways back and forth between CISC (logic quicker than memory access) and RISC (memory close enough to feed short logic paths). A decades old battle; reality settles in the middle. And nearly irrelevant, given modern compiler capabilities.

TJ

Re: Battery powered raspberry pi
 

I don't understand what you mean by this.
The Microchip PIC32 M4K MIPS RISC instruction set is a Harvard architecture (see page 3 of the link from Microchip below).
It also has interrupts.

I have some sitting on my workbench to my right.

http://www.microchip.com/stellent/gr...c/en542879.pdf

As far as CISC/RISC the answer is whatever actually gets the job done as far as I am concerned.
The same is true of interrupts as far as I am concerned.
The rules of thumb (acceptability) here are often a question of popularity rather than science.

Now in fairness - I've yet to find a use for the PIC32 in the projects I have in manufacturing. That does not mean I won't it's just been trumped by customer requirements, size constraints, cost concerns, and knowledge transfer concerns as several other chips I have laying about often are. It has plenty to offer just at the moment it offers more to me than to people I might sell it to (my requirements are always a different matter). So do I know about it yes. Am I a volume customer of the product no.

Re: Battery powered raspberry pi
 

This probably isn't the "right" way or the best but it was cheap and worked well... I used a 12v - usb car phone charger and a female car charger port thingy... Worked like a charm and only cost a few bucks...

Re: Battery powered raspberry pi
 

One thing to remember: You are an engineer, so don't say "This probably isn't the 'right' way". :)

Back on track, a 12v USB plug will be a lovely option because they are meant to run off a voltage this high from the robot battery. They can also handle quite a good amperage, and you'll get them real cheap!

Re: Battery powered raspberry pi
 

On the contrary, he can certainly say that. Particularly because he didn't use the definite, just the probable.

If an engineer says that something isn't the "right" way, he means that it's not the way you're supposed to do it, but it's a way that works--and may become the way you're supposed to do it, eventually. (A lot of R&D starts when someone finds a way that isn't the right way.)

But, that engineer could also mean that it's the WRONG way. In that case, you might want to listen, particularly if he says straight out that it's the wrong way.

Re: Battery powered raspberry pi
 

So anyways,

So we have been powering our pi directly from the PD board's 5V out. It seems to be powering, though I think the SD is corrupt because it is always hard-reset.

Re: Battery powered raspberry pi
 

Try disabling any sort of write caching in Linux.
This will force file commits immediately - but it will negatively impact performance.

Re: Battery powered raspberry pi
 

It's a nitwit idea. Nitwit ideas are for emergencies. The rest of the time you go by the Book, which is mostly a collection of nitwit ideas that worked.

From "The Mote in God's Eye" by Larry Niven and Jerry Pournelle

Re: Battery powered raspberry pi
 

You need a way to do an orderly shutdown. Perhaps send a message from the CRio when you transition out of teleop?

Re: Battery powered raspberry pi
 

That's on a testbot, so it won't be used in competition.

I had a wierd idea. Do you guys know about those USB cell chargers? What if we use it on the bot? Wouldn't it be a COTS part?

Otherwise, I thought of a fairly simple idea:

A Large capacitor powers the Pi. That is charged from the robot battery and goes in only one direction because of a protection diode. There won't be a very high voltage (maybe maximum able to give a tingling sensation), so this could power the Pi. Also, it should discharge in no time, down to 0v7, beyond the threshold to electrocute even a foolish person.

Here's a schematic

Re: Battery powered raspberry pi
 

Really lad to hear you're looking at everything. Like I inferred, I learn a lot every time you post. Been too deep in the transistors lately. It's amazing how a "bus matrix" (soon to be "bus fabric") helps marketing show whatever memory architecture they need to sell.


The more important question is how large a production run does one need on a "Pi/Arduio/whatever + shield(s) + battery + enclosure" to qualify as COTS?

Tim

Re: Battery powered raspberry pi
 

As far as I know the requirement for COTS is that you can prove the company that is producing the product is actually at production level, able to fill orders for a realistically large number of customers to be at a production level, answerable for issues with the product and not selling a product targeted only at FIRST. One can't be selling the product targeted specifically at FIRST because if you are using the COTS rule your product is very likely not FIRST specifically approved so therefore it's not in the KOP or the manuals.

I am sure there's a market out there for a ready-made enclosure with battery and loaded with platform of choice beyond FIRST. It's getting more and more unlikely that anyone can prove they are at production volume for this season. You'd have to: open or have a business (it can be done in <24 hours), engineer the product, test the product, put the product up for sale with adequate evidence it's advertised to the general public (it might take 4-6 weeks to get into a monthly periodical so that's out) and finally have sales. Seems pretty unlikely.

How much volume the initial run has to be is probably less relevant to success (where as it would matter to a FIRST approved product) than whether or not the business could meet delivery demands. People might wait weeks for a product like they did for the original batch of Raspberry Pi under the right circumstances. However waiting weeks pretty much ends any chances of working out during the 2014 season.

With 2015 right around the corner - a good question is will FIRST continue with the COTS rule and allow auxiliary computing devices once the RoboRio is the new standard? Will FIRST decide that the RoboRio eliminates the need? Personally I think the RoboRio does not eliminate the need for this rule but that's just my opinion.

Re: Battery powered raspberry pi
 

There are a few points in there I wouldn't agree with, but just commenting on the bolded. I don't see how you are getting that definition, how does targeting a product too FIRST teams make it not a COTS item and if it did, then a think a few of the parts FIRST teams take as COTS items, would stop being COTS. As a few retailers do target products to FIRST teams.

Re: Battery powered raspberry pi
 

Using the knowledge FIRST teams use your product to estimate the demand for your product is not really targeting first any more than estimating the number of people that read a particular periodical. Though it starts to split hairs when the only thing governing your production is FIRST. Really the assumption here is you are in business year round.

Targeting FIRST (in the sense I am stating it and from my perspective) for a product means making the product particularly appealing for FIRST and attempting to limit your production to only what FIRST might need. It also likely carries with it using FIRST resources like the name and/or affiliated websites to advertise.

The COTS rules in FIRST are really limited in scope to electronics. It's not that say a swerve is not COTS in the general sense but you don't need that rule to use a swerve module at all. You do need that rule for electronic items.

So if you going to make an enclosure, with a battery, a charger and some other computing device in it and use it under the COTS rule it would be asking for trouble if: you ever refer to it as the maker like it is specifically for FIRST, ever mislead people that it's FIRST approved by using say the logo, only make production runs based on FIRST usage, make any assurance that it is allowed in FIRST or only do support for FIRST teams.

Sure a team can make a custom circuit and share that circuit with another team. However it's not COTS unless it's really a product anyone (potentially everyone) can buy and it's sort of splitting hairs if it's entirely improbable to find a legit use for it outside of FIRST. However a custom circuit doesn't open the door to the extra battery like a COTS computing device does.

Others may interpret this rule differently. However in my perspective as a business person if I am really targeting FIRST I really ought to get FIRST's approval. In the course of all conversations I had with FIRST about potentially making something like this as COTS I made it quite clear that if I did that myself it would be for sale with no mention of FIRST. If someone from FIRST uses it - that's their choice and not the result of my marketing. Any action I took that would effect FIRST would be no different than any action I would take for any other customer and especially while dancing this line I wouldn't give the product away for free to any team unless I am going to give it to all the teams like via the KOP. Effectively I wouldn't solicit public review from just FIRST relations or participate in such reviews publicly because that's unusual for general products.

Could someone get away with operating on a different understanding of this rule: I am sure they could. I wonder though if they really understand the liability they are creating for themselves.