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2476  Forum 2005-2010 (read only) / Bar Sport / Re: water solenoids? on: December 22, 2008, 11:00:41 pm
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Typically the garden sprinkler solenoids are 24V AC, but they work just as well with DC.
huh?  You sure about that?

I haven't tries the solenoids, but I got a DC relay by mistake once and hooked it up to 24VAC - made a heckuva racket until I got the power killed.   Most definitely was not interchangeable...

-j

2477  Forum 2005-2010 (read only) / Bar Sport / Re: water solenoids? on: December 22, 2008, 12:33:43 pm
If you don't want to use relays, a solid state relay (SSR) would work, or at loads as low as this a discrete TRIAC would probably be the switching device of choice.  I'm pretty sure the sprinkler controller I've seen uses TO220 sized TRIACs for switching the AC side.  The conformal coating was such that I couldn't read any part numbers. smiley-sad

I googled a spec sheet that says 20 to 80 PSI pressure range, 0.3A inrush/0.2A hold current at 24VAC.  I would guess this to be pretty typical.

If you're operating with effectively no pressure (i.e. gravity flow) a simpler valve such as the refrigerator or washing machine type may be more appropriate, as I think these are direct acting rather than a diaphragm type like the sprinkler valves.  They'll typically operate on 120VAC; you'll switch them with an appropriately rated relay, SSR, or TRIAC.

The only windshield wiper systems I'm aware of (which is a very short list) are pumps, not solenoids, as they're simply pumping from a reservoir that's lower than the outlet.

-j

2478  Forum 2005-2010 (read only) / Bar Sport / Re: water solenoids? on: December 22, 2008, 10:47:24 am
You can get sprinkler system solenoids at the local BORG (home center) that operate on 24VAC for about US$20 each, IIRC.  The 24VAC transformer should be nearby.

You'd have to switch AC current with the arduino, but that's doable, and in exchange you get a reasonably cheap and ready supply of valves.

-j

2479  Forum 2005-2010 (read only) / Bar Sport / Re: POST YOUR WORKBENCH on: March 31, 2010, 02:14:11 pm
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I think we may be talking about different kinds of shelving.
Yes, we are.  I'm talking about shelving like this mounted with clips like these.  The shelves themselves would be OK if they were lined and had a decent support system.

-j
2480  Forum 2005-2010 (read only) / Bar Sport / Re: POST YOUR WORKBENCH on: March 30, 2010, 08:51:30 pm
It's not finding replacements (or even buying them, they're cheap), it's cleaning up the mess.  Last time it happened to me, it was exploding car-care products (polish, tire cleaner, etc etc) that made a huge stinkin' stainin' mess in the garage.

Environment doesn't seem to matter; those in the bedroom closets went first (climate controlled and dark no UV!).

You've probably got 8 or 10 years before it starts happening to you. smiley

-j
2481  Forum 2005-2010 (read only) / Bar Sport / Re: POST YOUR WORKBENCH on: March 30, 2010, 07:22:10 pm
Wire shelving is something I've grown to despise.  Small objects fall through, and after a few years the plastic supports get brittle and a little bump (or nothing at all) causes a cascade failure of all the age-brittle plastic and the whole shelf (and any shelves under it) fall in the floor.  And I'm not in earthquake country. smiley. It's especially entertaining when it happens in the middle of the night and you're sound asleep.

-j
2482  Forum 2005-2010 (read only) / Bar Sport / Re: POST YOUR WORKBENCH on: March 30, 2010, 01:14:28 pm
cr0sh has some good points (but I disagree about the pegboard - it's a huge waste of surface area, compared to drawers/shelves/etc.  I'm pulling it down in my shop).  Definitely don't get cheap on the furniture and shelving.

I like fishing tackle boxes like these for the plastic storage boxes.  It's like several small boxes in one, and you have some reconfigurability.

I'm ambivalent about the boxes of small drawers for parts. I've got one, and got stuff in every drawer, but there's plenty of unused space.  I'm thinking of a rack of storage boxes instead (got plans to build the rack, just haven't had time yet).

For components, small parts, and small projects I use tackle/storage boxes (Plano 3700 series is my favorite).  An Arduino with a shield or two will fit in a 3730 compartment, and components bagged in small ziplocs which are grouped by size/type/etc will store quite efficiently in there as well.

-j
2483  Forum 2005-2010 (read only) / Bar Sport / Re: Higher rated capacitors = closer tolerances? on: April 03, 2010, 01:48:42 pm
A couple of poster have implied (but not stated) a good point:  if one device is listed as 1.00uF and the other is listed as 1uF, it is implied that the 1.00uF is a tighter tolerance than the 1uF (but always check the datasheet to see if the manufacturer knows the rules about significant digits).

-j
2484  Forum 2005-2010 (read only) / Bar Sport / Re: Anyone tried the Propeller Chip? on: February 26, 2010, 07:51:41 am
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Really?  No Ethernet shield?  No WiFi shield?  No serial motor controllers?  All of those use non-ATMega CPUs,  usually because they need capabilities not available in an 8-bit AVR.
I'm not 5 years old, and I'm not starting the Church of the AVR or anything. :|  I do have an ethernet shield (homebrew adapter for the Wiznet module that matches the official shield) and have made several other shields that use non-AVR components.

I just prefer to develop on a mac ('cause I like computers that work) and I like gcc because it's a good compiler, and free.  The ATmega lines up with those preferences nicely.

I also prefer my tinkering projects to be friendly, or at least non-hostile, even if I don't expect them to be easy.  No hardware support for anything sounds decidedly unfriendly to me.  In fact, it sounds more like a microprocessor than a microcontroller.  Been there, done that, like a microcontroller better for my little projects.

And sorry, comparing lack of ethernet support to lack of UART support is nonsense in a microcontroller context.

-j
2485  Forum 2005-2010 (read only) / Bar Sport / Re: Anyone tried the Propeller Chip? on: February 25, 2010, 02:46:07 pm
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weirdly,  with no hardware multiply/divide.
Not much hardware, period.  No UART - want to do RS232 communications? dedicate a cog to bit-bang it.  As you've discovered, no I2C or SPI.  There goes 2 more cogs, if you happen to need all those at the same time.

Lots of folks get excited because it can generated video.  Too bad it's a one-trick pony.

No thanks, I'll stick with my ATmega, running avr-gcc on my mac.

-j
2486  Forum 2005-2010 (read only) / Bar Sport / Re: Hot Air Rework Station? on: February 07, 2010, 07:02:41 pm
watch ebay for a Hakko 850 or 852.  I got a slightly used 852D for a few dollars more than the cheap chinese clone.

-j
2487  Forum 2005-2010 (read only) / Bar Sport / Re: Position updation..? on: February 03, 2010, 10:08:16 am
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Is it because you can't use re-raditating antennae
Er, if you use a re-radiating antenna you'll know where the re-radiating antenna is, not where the receiver is...

-j
2488  Forum 2005-2010 (read only) / Bar Sport / Re: Altimeter? on: December 24, 2009, 03:03:55 pm
I've considered using a combination GPS and pressure sensor.  My theory is that the payload (rocket or balloon) will spend some time on the ground, and the GPS can lock and obtain a relatively accurate altitude measurement which would be averaged.  This would be used to adjust the pressure altitude from the pressure sensor.  I'd need a GPS anyway, for lat/lan position reporting.

-j
2489  Forum 2005-2010 (read only) / Bar Sport / Re: Altimeter? on: December 24, 2009, 12:54:27 pm
GPS altitude precision sucks, especially if you're moving.  I suspect averaging would help.

A pressure sensor is a lot cheaper, but as you point out pressure altitude varies with weather.

Rocket altimeters seem to work on AGL vs. MSL - i.e., relative altitude instead of absolute.  This neatly sidesteps the problem.

I've got working code for the Freescale MPXAZ6115/MPXHZ6115 sensors.  The Perfectflite avionics use this one.

-j
2490  Forum 2005-2010 (read only) / Bar Sport / Re: Why is the Arduino Mega so expensive? on: December 21, 2009, 02:40:44 pm
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The extra headers and the size of the PC board can't add that much to the cost.
You apparently haven't priced headers. :|

PCB cost is per unit area, and the MEGA board is twice as big as previous generations.

So, 4x the cost for CPU, 4x the headers, and 2x the PCB area, for only 2x the price.

-j
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