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46  Using Arduino / Motors, Mechanics, and Power / Re: electronically controlled reed valve ? on: March 03, 2014, 05:34:06 pm
How about a rotary gate shutter driven round by a servo motor.  Something like the device used on the old style cinema projectors. See here for a cartoon of one  http://en.wikipedia.org/wiki/Rotary_disc_shutter
47  Using Arduino / Motors, Mechanics, and Power / Re: ideas for mini garage door opener on: March 02, 2014, 05:42:50 pm
Might be better with a winch rather than a wench, though a wench would probably be more fun
48  Using Arduino / Motors, Mechanics, and Power / Re: ideas for mini garage door opener on: March 02, 2014, 04:23:14 pm
A continuous rotating RC servo motor driving a spool drum should fit the bill.  You can either drive it for a fixed period of time (a known number of revs)  to control the movement range or fit some small micro switches at top and bottom to manage the servo controller.
49  Using Arduino / General Electronics / Re: LM317 heat on: February 28, 2014, 06:04:04 pm
Relay contacts have to be "self cleaning" and they use the energy of the spark at the time of opening to perform the cleaning.  Contacts (generally silver plated) which carry extremely little current will eventually oxidise and fail to provide a good electrical circuit unless either gold plated or hermetically sealed.  Platinum used to be used as high integrity contact points for MIL-spec relays.
50  Using Arduino / General Electronics / Re: LM317 heat on: February 28, 2014, 11:55:13 am
Why not save yourself the 317 and simply put a 270ohm resistor in series with the relay feed from the switching transistor.
51  Using Arduino / Motors, Mechanics, and Power / Re: board protection from car electrics is this gonna work ?? on: February 27, 2014, 09:52:10 am
You're missing the diode used to get turn-on volts to the circuit side of the FET

Your arduino on-board regulator circuit won't like you trying to run it from 24 volts (even for a short duration) so you might want to look at providing a 12 volt regulated supply dedicated to arduino power feed only (to minimise heat loading)
52  Using Arduino / Motors, Mechanics, and Power / Re: Will TIG noise be a problem? on: February 25, 2014, 05:35:42 pm
Can't offer and answer to the question but have you considered the TIG aspect of the problem.
How do you plan to connect the TIG welding ground lead to the lazy susie plinth-plate.  If you connect to the static bearing housing their balls will literally burn up.  You will need some sort of sliding brush contact that electrically connects directly to the table shaft or the table plinth-plate.   Also bear in mind that the weld current will probably be in the range of 20 to 200 amps so the ground lead/contact system will need to be substantial.
53  Using Arduino / General Electronics / Re: Question about resistor tolerance on: February 25, 2014, 05:25:17 pm

So there is no need to use a precise resistor value to set the LED current: you can use a lower value if the light output is satisfactory, or a slightly higher value provided the absolute maximum value quoted on the datasheet is not exceeded. 

"Higher and Lower" might be confusing to a beginner.  The "lower value" refers to current (achieved by using a higher value resistor) and "higher value" again refers to current (achieved by using a lower value resistor)
54  Using Arduino / General Electronics / Re: Question about resistor tolerance on: February 25, 2014, 01:51:32 pm
Use a 150ohm.  Slightly lower current will flow through the LED but I doubt you'll notice.
How did you establish your 125ohm value  -  based on maximum LED current or what
55  Using Arduino / General Electronics / Re: replacing pot with resistor on: February 22, 2014, 04:40:46 pm
You can of course use a potentiometer as a variable resistor, proper name rheostat, by using one fixed terminal and the wiper terminal as the two system lines  It's also good practice to connect the remaining fixed terminal to the wiper so that, in the event of the wiper lifting from the track, the system will "see" the the potentiometer full resistance value rather than an open circuit.
56  Using Arduino / General Electronics / Re: measuring ON time and off Time of PWM pulse on: February 22, 2014, 08:00:20 am
As MarkT says, use a multimeter, but make sure it's an analogue one (with a moving pointer).   The mechanical inertia of the movement will even out the pulses and give a rough indication of duty cycle.
57  Using Arduino / Motors, Mechanics, and Power / Re: Putting three lead acid batteries in parallel on: February 21, 2014, 01:44:21 pm
But not how it's been shown.  B2 is the wrong way round for that technique. 
58  Using Arduino / General Electronics / Re: Component packaging. on: February 21, 2014, 01:40:01 pm
a few seconds in the microwave should sort out your concerns

ONLY JOKING  --  DO NOT DO THAT  !!!!!   smiley-twist smiley-twist smiley-twist

I really don't understand your concern.  The components, once removed from a packet (sealed or otherwise), are exposed to the humidity of your environment, irrespective of what that may be.    Unless the items are actually wet there should be no cause for concern.  The  component internals are hermetically sealed so external humidity only acts upon the leads.

I'm sure most reputable suppliers go to great lengths to ensure their products are not immersed prior to sale.
59  Using Arduino / Motors, Mechanics, and Power / Re: Putting three lead acid batteries in parallel on: February 20, 2014, 05:33:30 pm
There is no right answer; just wrong and wronger.  You pays your money and takes your pick.   smiley
60  Using Arduino / Motors, Mechanics, and Power / Re: Putting three lead acid batteries in parallel on: February 20, 2014, 01:44:49 pm
My grey cells were clearly in a spin when I made my comment about increased duration.  smiley-red smiley-red

What I was actually trying to convey was that system current would be reduced by a factor of three.

By placing batteries in parallel, the OP was endeavouring to increase battery capacity to 21AH at 12 volts, so total power available would be 252WH and he would be assuming that current load would be evenly distributed across all three batteries.
For example, say motor rating was 200W, then system current would be 200/12 = 16.67 amps.  Ignoring any loss of capacity due to discharge rate, the potential duration would be 1.26hours

However, if the motors were in series the battery system would be 36 volts at 7AH.  Again total power available would be 252WH.  However with the 200W motor, the load current would now be 5.56amps.  Duration would remain at 1.26 hours

There are benefits to be gained by having batteries in series (increased voltage)
a) the same discharge current flows through all three batteries so each gets discharged evenly
b) the same charge current flows through all three batteries so each gets an improved chance of being charged evenly
c) by reducing system current by a factor of 3, the I2R losses would be reduced by a factor of 9 so the system is electrically more efficient.

Apologies for any confusion caused.

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