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1  Using Arduino / Sensors / Re: is there anyway to make smaller antenna for FPV system ? on: September 15, 2013, 08:54:50 am
you have nice copper wire inside coax cable.
copper core of your tv coax will probably do just fine as an antenna. just strip it, cut it and solder it.
2  Using Arduino / Sensors / Re: is there anyway to make smaller antenna for FPV system ? on: September 15, 2013, 08:43:32 am
if you have a piece of decent 75 ohm coax, why would you want to attach antenna to it?
just use cable's core as the antenna. strip it to needed lenght making shure that the screen doesn't touch it, then solder other end to the antenna output, solder screen to the ground and you should be fine.

tv coax will be a pain to work with though. those are rather thick and not very flexible. not exactly something good for RC imo
3  Using Arduino / Sensors / Re: is there anyway to make smaller antenna for FPV system ? on: September 15, 2013, 08:18:34 am
youse whatever wire you have. a piece of old extention cable will probably work good btw.
of course you'll have to solder it. how else would you attach it? smiley-wink
the only question is if you want to connect your antenna directlt to the PCB or you want to put it somewhere else in which case you'll need to use a piece of propper coaxial leed (soldering antenna directly would be way easier though).
4  Using Arduino / Sensors / Re: is there anyway to make smaller antenna for FPV system ? on: September 15, 2013, 04:11:14 am
i would use a wire with insulation on it.  this way you won't have to worry about it. 1 - 1.5 mm^2 copper wire should be riggid enough to keep it's shape on it's own anyways.
in any case any plastic/rubber will do (as long as it's not coductive)
5  Using Arduino / Sensors / Re: is there anyway to make smaller antenna for FPV system ? on: September 14, 2013, 11:46:45 pm
any not coductive adhesive should do. i usually use simple hot glue for that stuff
1mm should be fine smiley-wink
6  Using Arduino / Sensors / Re: Sensors to measure volume change, weight and distance on: September 14, 2013, 10:43:26 pm
check this one out: http://www.ebay.com/itm/Balluff-BOD-26K-LA01-S4-C-Laser-Distance-sensor-NEW-/231041331307?pt=LH_DefaultDomain_0&hash=item35cb22f06b&_uhb=1

advertised 0.08mm reesolution
spect here: http://www.murri.fi/documents/balluff/BOD/BOD26K_LA01_S4_C_en.pdf
7  Using Arduino / Sensors / Re: is there anyway to make smaller antenna for FPV system ? on: September 14, 2013, 08:02:44 am
if you really want to build your antennas, then that's how i would do it:

wire antenna for the car:
1/2 or 1/4 wave lenght. your wave lenght is ~333.333mm so the antenna would be 166.666mm (1/2 wave) or 83.333mm (1/4 wave). use copper wire and keep it as straight as possible. curved antenna won't perform too well, but might work for you on short distances.

if you want high gain directional antenna for your reciever:
bi-quad design is probably the simplest to build. you can calculate dimensions here: http://www.changpuak.ch/electronics/bi_quad_antenna_designer.php


8  Using Arduino / Sensors / Re: is there anyway to make smaller antenna for FPV system ? on: September 13, 2013, 08:40:39 pm
actually you are in luck. since it's 900MHz, you'll find planty of different antennas on ebay. just look for GSM antennas (yes - for cell phones).
it all dependes on your transmitter's output power, but i'd imagine that you could easily install tiny antenna on your RC car, and compensate for weeker signal by using higher gain antenna with your reciever.
that's how people usually do fpv - small stuff in the air/field/whatever and high gain antenna (usually directional btw) next to the monitor
9  Using Arduino / Sensors / Re: Sensors to measure volume change, weight and distance on: September 13, 2013, 07:19:53 pm
i honestly don't know how acurate is this thing. all i know it has 1024 step resolution, because that's the reading i get after hooking it up to the computer (and that's not sensor's accuracy, but A/D converter's resolution) smiley-wink

a quick google search gave me this: https://www.mysick.com/ecat.aspx?go=FinderSearch&Cat=Row&At=Fa&Cult=English&FamilyID=380&Category=Produktfinder&Selections=77544 it suppose to be acurate to 1µm.
it's a red laser so if your container is made with clean glass and it has flat walls, then the reading shouldn't be much affected. you might want to look for something a bit cheaper on ebay though smiley-wink
10  Using Arduino / Sensors / Re: Sensors to measure volume change, weight and distance on: September 13, 2013, 06:05:49 pm
you could probably rig a little servo to lift your sample before every mass mesurement. this would allow you to set "zero point" automatically every time.
as for distance, i think optical reflection sensor would be your best bet. i have those installed in my digital wah-wah pedal (15 milimeters movement with 1024 steps) smiley-wink.
but this sollution would prolly still require you to put little reflector on top of the sample. it might me small piece of tin foil so hopefuly it won't affect your experiment
11  Using Arduino / Sensors / orientation sensor on: September 13, 2013, 05:18:43 pm
hi
i'm planing on constructing little flight recorder for RC plane.
the thing should read pitch, yaw and roll few times a second and save it on sd card along with RTC reading.
i have everything pretty much nailed, but i'm not sure what kind of orientation sensor to use.

can you guys recommend something that would give me 3 axis reading with 360 degree range without beiong affected by changes in speed?
12  Using Arduino / Motors, Mechanics, and Power / Re: h-bridge - probably stupid question.... on: July 29, 2011, 05:59:52 am
ok. i've done some reading and i found this:

the omly mod. i've made was replacing single transistors with darlington pairs.

it seams to work in simmulation, but i want to ask u guys for opinion before i'll start soldering smiley-wink

and yes - my skills with transistors are slim to non, but i do know how to plug them into tester in multimeter smiley-wink
13  Using Arduino / Motors, Mechanics, and Power / Re: h-bridge - probably stupid question.... on: July 28, 2011, 12:21:28 pm
Don't you usually use half NPN, half PNP?
yes, but if you have 300 NPNs for less than 4 euro then why use PNPs smiley-wink

14  Using Arduino / Motors, Mechanics, and Power / Re: h-bridge - probably stupid question.... on: July 28, 2011, 11:34:16 am
motor is tested and working.
there are no resistors whatsoever - circuit is exactly like shown on the pic.
transistors are working - i've just tested all of them.
i can turn on one of them using +5V from arduino....
so i'm guessing i need to add some base resistors to limit current, am i right?

15  Using Arduino / Motors, Mechanics, and Power / h-bridge - probably stupid question.... on: July 28, 2011, 10:31:32 am
so i've made that h-bridge using 4 BD135 NPN transistors (http://www.fairchildsemi.com/ds/BD/BD135.pdf), but it doesn't work...
schematic:


what am i missing?
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