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1216  Using Arduino / Project Guidance / Re: LED Lightbulb and Arduino Control on: February 17, 2013, 02:41:58 pm
You never want to control a LED with voltage only; once you reach the forward voltage of the LED (Vf) the current starts to ramp up very quickly with very small increments in voltage. A LED should always use a current controlled supply if you want reliability.

I'd suggest poking around on eBay for an AC LED driver; they're so cheap it's impossible to beat them with a DIY approach.
1217  Topics / Robotics / Re: Rotary encoder together with arduino for measuring angle on: February 17, 2013, 02:29:50 pm

Absolute encoder with 128 positions. Under $7.
1218  Using Arduino / LEDs and Multiplexing / Re: Maths Guru ? or of course, a simpler approach in the first place ! on: February 16, 2013, 01:36:50 pm
Problem is, for a power level of 25 out of 50, I am actually sending 25 ONs, followed by 25 OFFs.
That delay (25 continuous OFFs), is now limiting how expandable the system will go.
e.g. if I want 100 power levels, or control other devices that require/benefit from more constant signals.
The ideal situation would to alternate, ON then OFF, 25 times.

This is the same kind of problem as drawing a straight line from (0,0) to (50,25) across a grid. The solution to that problem is the Bresenham algorithm; every time the line would increment up the Y axis you would turn the signal on, and every time you don't increment you would turn the signal off.

When you figure it out the code will be just ~10 lines. I can provide an example but I'm certain you won't understand it without first attempting to work it out yourself.
1219  Using Arduino / Project Guidance / Re: SX1509 16 Output I/O Expander Breakout on: February 16, 2013, 01:20:18 pm
You want either a shift register or a TLC5940. The chip you have linked really isn't designed for a lot of power.

"5.5V tolerant" means that its normal signaling voltage is only 3.3V but it will accept a 5.5V input.
1220  Using Arduino / General Electronics / Re: Current measurement on positive or negative side? on: February 15, 2013, 07:46:13 pm
Your motor rating is only 3kW (4HP) assuming 100% efficiency.  This seems far too small for a lawn tractor.

For a comparison you could look at the old GE "Elek-Trak" models -- the most popular model 12 was 1.5HP for the drive motor. They carried six batteries and ran at 36V.

The motors are replacing a 13hp ice motor (maybe the right term is ride-on lawnmower rather than tractor). So about 4 hp for drive, which I think is more than enough, and about 4 hp for the blades which might be too little, but if it works I’ll probably be happy to cut the grass before it gets to long. With this setup, I can also eliminate some pulleys and the clutch, which hopefully will reduce the power requirements a bit. I’m going to use four 85ah marine batteries, and I’m hoping to get a couple of hours juice for just driving, and maybe 40 minutes of grass cutting.

That sounds about right to me.

The Arduino will try do reduce power to 130 amps per motor, and will allow 150-200 amps for max 5 seconds, and will shut of power completely if consumption is more than 200 amps for one of the motors.

You should still use a breaker or fuse for overcurrent protection.
1221  Topics / Robotics / Re: Rotary encoder together with arduino for measuring angle on: February 15, 2013, 11:57:05 am
How much precision do you need?
1222  Using Arduino / General Electronics / Re: Transistors and Resistors on: February 15, 2013, 11:24:29 am

As an aside, 5mm LEDs with 100ma forward current (e.g. TSAL5100) are quite a bit cheaper than those larger, star emitter types. You shouldn't have any problem finding those from local distributors and won't feel as bad burning up a ~$.25 part as compared to a $5 part.

1223  Using Arduino / General Electronics / Re: Transistors and Resistors on: February 15, 2013, 06:38:10 am
There shouldn't be a need for a transistor for a camera button. Any switching requirement that required a high amount of current would be a very wasteful (battery wise) design. Unless you're trying to activate a mechanical apparatus (solenoid) to press the button there is assuredly a simpler way to do it.

To clarify what Mike said, base resistors are critical but the value usually isn't; always try to limit the current from your pins to 20ma.
1224  Using Arduino / General Electronics / Re: Current measurement on positive or negative side? on: February 15, 2013, 06:14:23 am
Does I understand this well? You have a motor that "eat" 130 amps @ 24V smiley-eek-blue smiley-eek-blue
If I were to wager a guess I'd say "hydraulic power pack" like jonisonvespaa described. Common on snow plow trucks or dump trailers.
1225  Using Arduino / Sensors / Re: Need ideas on tachometer using ignition on: February 15, 2013, 02:01:42 am
I meant, will a photo detector be able to read that many flashes a sec?
Phototransistor or photodiode certainly would. You don't want a photoresistor (CdS cell).
1226  Using Arduino / Motors, Mechanics, and Power / Re: Device to hold and release Mouse Trap. on: February 14, 2013, 01:04:55 pm
Reminds me of this ball launcher:

Well, maybe a bit abstract as applies to a mousetrap but hopefully you'll get the idea.
1227  Using Arduino / General Electronics / Re: TLC5940 - 1st works, 2nd not :/ on: February 14, 2013, 03:59:28 am
Oh snap.

So you why don't you have the SCLK connected between the chips? Each chip will need that signal.

Not clear on the purpose of the GSCLK but it seems that should be connected as well.
1228  Using Arduino / Motors, Mechanics, and Power / Re: Big easy stepper motor not changing direction. on: February 14, 2013, 03:07:12 am
Im sure its alle wired up corectly but its not changing direction when I run the program-

Does that mean that you're reverse the counting in the program or what?
one direction: 00, 01, 11, 10,...
other direction: 00, 10, 11, 01,...
BigEasyDriver has a step/dir two wire interface.

OP, what program are you using to drive it?
1229  Using Arduino / Sensors / Re: Ds18b20 long wire problem on: February 14, 2013, 02:46:25 am
Maxim provides an appnote discussing this:

If you want better answers you should provide more detail as to your topology and how long your cables are.
1230  Using Arduino / Sensors / Re: Is it possible to use the Sensors for this on: February 14, 2013, 02:41:35 am
Look for IR reflectance sensors used for "line following" robots. sells a few and provides theory/schematics/instructions.
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