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Old Apr 24, 2009, 09:19 AM
PLD
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Idea
Design incubator - where good ideas come to grow

Got an idea for an electronics device and think that we might be able to turn it into a reality for yourself and the rest of the R/C community? Let us know about it here and see where it can go

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Old May 15, 2009, 12:37 AM
PLD
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Okay, for the last few years I've been thinking about making my own altimeter, and now I'm feeling good about some of the sensors I've found on the market, specifically first up the Motorola/Freescale MPXA units which give a very nice "practical" output going from 0 to 5V from 15kPa -> 115kPa respectively (115kPa being roughly sea-level).

Of course, that's the easy bit - the question is, given that there are already many other altimeters out there, what can I do to make them more specific or get into a market niche?

One idea I had was to lug on a 433MHz transmitter and be sending out the altitude constantly, though that'll push the costs up considerably, mostly due to the base-station.

There's a range from the dead-simple devices that just record the maximum height, or the logging devices that handle minutes/hours of data. One thing that -has- always irked me about the existing devices is the absolute lack of support beyond Windows software, now I know 90% of the population uses Windows but there's a higher density of geeks/Linux/Mac users in RCGroups and I'm one of them. Personally I'd rather write software that works on -all- the OS's.

Paul.
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Old May 15, 2009, 01:52 AM
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Paul,

If you can come up with a "low" cost altimeter that can say record a single flight profile in presettable increments which could then be down loaded to a "low" cost hand held gadget??????????

or

Same as above transmitting to a simple receiver in presettable increments, just a data logger, no displays or such like to keep the cost down???????
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Old May 15, 2009, 02:03 AM
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Neil, the primary cost killers in this concept are as follows;

* pressure sensor ($30 AU each... trying to find a better supplier of course )
* Telemetry link (roughly $40 AU for the pair including matched antennas)
* Output display... could use a 128x32 pixel display... did I mention costs? ($20+)
* Casing, if we're going with a hand-held readout, it's going to bite (it's a big stalling factor on the PIRCAT too).

If the sensor wasn't so insanely expensive things would be a lot easier. I can probably purchase them direct from Freescale but it'll likely need to be at least 100 unit purchases, that's a lot of cash up front.

I must say though, it'd be doubly nice if you could actually just slot a micro-SD card into it and pop that into the computer when you're done, save having to link a cable up all the time and you could use multiple cards for the day's events.... okay, getting over my head again.

Paul.

Paul.
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Old May 15, 2009, 02:08 AM
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Quote:
Originally Posted by pldaniels
.........I must say though, it'd be doubly nice if you could actually just slot a micro-SD card into it and pop that into the computer when you're done.................
I really like this idea. A 2 or 4 gig SD could hold how many flights
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Old May 15, 2009, 02:22 AM
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A stupidly insane number of flights/duration. If you store a 2-byte value every 0.1 seconds, 20bytes/sec .. and there's 2,000,000,000 bytes in a 2GB SD stick... that gives us a nice long long period of time... crazy long. . . . makes you start wanting to do things like putting a temperature and voltage sensor... and... and... here we go again.
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Old May 15, 2009, 02:54 AM
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I've got a pair of the pressure sensors being shipped to me now - probably will take about two weeks, that gives us enough time to bash through a few dozen ideas.

Realistically, adding a voltage and temperature sensor to the mix isn't hard, since all the hardware is already there and the microcontroller can deal with at least 8 different inputs. There's more work in the software side of things, though I've actually already written an application that's portable which could be adjusted... of course there's always Java *bleah*.


Paul.
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Old May 15, 2009, 05:15 AM
ancora imparo
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Paul, don't forget my "flying fuel gauge" idea. Would be a doddle to add to this if you already have the uC with ADC and 433 link in place. Would certainly be a marketing edge since no one else offers that AND it's insanely useful.

Quote:
Originally Posted by pldaniels
Realistically, adding a voltage and temperature sensor to the mix isn't hard, since all the hardware is already there and the microcontroller can deal with at least 8 different inputs. There's more work in the software side of things, though I've actually already written an application that's portable which could be adjusted... of course there's always Java *bleah*.


Paul.
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Old May 15, 2009, 05:21 AM
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John,

I think I should just wrap up one of those tiny Asus eeePC's and put it in the plane the way features are being added (I tease, I tease!).

A fuel gauge could be a nice top up if we're going for the do-everything-and-kitchen-sink system. Of course then I have to come up with a coulomb counter to keep track of things, that makes things harder since you either have break the power line or add a hall sensor / current-sensor. For 1~5A it's not a problem, just place the whole gadget in the middle of the line and stick a 0.005R shunt in the way.

Paul
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Old May 15, 2009, 05:33 AM
ancora imparo
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Remember the info I sent you on the Raztec Hall Effect sensors? Slip over a battery wire if using bullet connectors or use a plug through Deans Male/Female. That's what I had in mind. I did an analog circuit mock-up using an LM331 and 433 modules and it worked fine. Resend you the info if you want. Would add only a few grams, 0-80A linear (less range/more precision with multiple turns). Optimised for 3.3 or 5V supplies. The Coulomb counter doesn't have to be in the airborne unit - it's actually more sensible to have it in your ground display unit I would think.
Quote:
Originally Posted by pldaniels
that makes things harder since you either have break the power line or add a hall sensor / current-sensor. For 1~5A it's not a problem, just place the whole gadget in the middle of the line and stick a 0.005R shunt in the way.

John

Paul
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Old May 15, 2009, 10:45 PM
PLD
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John,

Yes, still got those links

I was thinking for sub-5A loads it's cheaper/simpler/more-compact to go with something like a 10~50mR 1206 or 2512 size resistor shunt, since it can be placed on the board very compactly.

Paul.
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Old May 15, 2009, 11:26 PM
ancora imparo
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Paul, you know I'm persistent!

What's the point of a <5A in-flight current sensor? What I'm suggesting is a low cost simple equivalent of the Seagull telemetry system for us ordinary folks. Bet there's a real market for something that tells you exactly how much capacity you have left in the battery at any time during a flight. If you are doing the altimeter and RF link in any case, why not look at a useful, real-life current draw, additional function that adds virtually no weight and maybe $2:00 cost?

Do have a look at the Raztec specs. They are rugged as a rock, only 1g in weight, a 3.5mm bullet passes right through (or even thicker wire without a connector), and they mount direct to the board with three pins. How much simpler can it get? NO power loss and NO current limitation. I'd make one myself in a shot if I had your uC skills and knowledge but I don't so the best I can do is persuade someone cleverer to do it instead.

I'll send you my sample if you want to have a play with it.

John

Quote:
Originally Posted by pldaniels
John,

Yes, still got those links

I was thinking for sub-5A loads it's cheaper/simpler/more-compact to go with something like a 10~50mR 1206 or 2512 size resistor shunt, since it can be placed on the board very compactly.

Paul.
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Old May 15, 2009, 11:38 PM
PLD
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John... persistent? really?

Well, really there's two things to chase here --- I really just want a simple altitude device first up, not sure I want to try chasedown/design a full spec system that'll do everything... yet. . . . then I must get that 4-wire/PIRCAT system sorted out.

The universal IRM is proving to be a bit of a pain but I've got it mostly licked (cough). The method I'll use is to probably supply-isolate the voltage drop sensing system from the processing side and opto-link them for the data-transfer. It makes things a little bit bizzare in that I'll have added circuitry just to do the DC-DC isolation (though it'll probably be cheaper these days to simply buy one of those very handy 5V-5V blocks, they're about $10 and provide 1kV separation). The best thing then is that if something 'strange' happens on the cell input it won't destroy things.

Paul.
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Old May 19, 2009, 02:02 AM
getting thorney
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i need a simple light weight switch that i can fire an onboard booster rocket with, i need it to plug into a spare channel on my reciever and put out 9v from a remote battery (square ones) as to not interupt with the standard internals.

for now the tests will be carried out on a cheep 2ch glider thats 330g with a c6-0 estes rocket which i dont think will be stupidly fast...i hope
will be stepping it up to an x-1 slope glider thats got "ignition" like its true form

hope you can help or sugest something thats already been used
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Old May 19, 2009, 02:22 AM
PLD
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Jay,

Yep, I've got something pretty similar to what you're after. The existing PLD-RCS-1A ( http://nqrc.com/?vp=PLD-RCS-1A ) would have to just be wired slightly differently to allow you to use the 9V battery.

Paul.
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