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991  Using Arduino / General Electronics / Re: Substitute for a reed switch? on: March 26, 2011, 03:15:09 am
The obvious question -

Why don't you want to use a reed switch ?   They are simple, cheap and utterly reliable
992  Using Arduino / Motors, Mechanics, and Power / Re: Need help with simple problem on: March 23, 2011, 05:39:01 pm
Are your servos powered from that small pack of 4 AA cells.  If so I don't think it'll run 5 servos every 10 seconds for very long before it becomes depleted - certainly not "ad infinitum".  In fact if all 5 servos are commanded to move at the same they may pull the voltage too low to operate satisfactorily.
993  Using Arduino / Motors, Mechanics, and Power / Re: will this SSR work for Arduino? on: March 23, 2011, 05:31:22 pm
I know it's obvious but remember to use a digout, not a PWM.
jack
994  Using Arduino / General Electronics / Re: Battery pack to power a camera on: March 23, 2011, 11:28:22 am
Forget AAs.  If you are building an external pack then use a pair of D sized cells.  If you use decent ones you should get many hours of photography from them.  Using cells in parallel is no substitute for using larger cells.
995  Using Arduino / General Electronics / Re: Finding reed switches? on: March 22, 2011, 03:56:24 am
Bicycle speed/distance "computers"
Domestic water/shower booster pumps (flow sensing)
Central heating boiler water flow sensor
Miniature DIL relays
Wind direction indicators (the cheaper ones use 8 or 16 reeds)

996  Using Arduino / General Electronics / Re: Measuring current on: March 22, 2011, 03:48:48 am
Think low tech
Put a black bag over it
997  Using Arduino / Motors, Mechanics, and Power / Re: Stopping stepper if an obstacle is detected ? on: March 20, 2011, 11:26:46 am
Correct me if I'm wrong but isn't the current in a stepper motor independent of the load on the shaft.  After all, all you are doing is providing a rotating magnetic field which is being followed by a permanent magnet. The strength of the field and the magnet is what determines the output torque and all you are effectively doing is switching field coils on or off to produce a fixed field "rotational effect"  

Edit :  I suppose at high speed (pulse rate) there is some back emf induced into the coils by the rotor which will tend to reduce the coil current but at low rotation speeds or when simply jogging this effect must be minimal so coil resistance (or rather reactance) will determine current irrespective of whether the rotor is free to rotate or jammed.  There may however be some "signal" induced into the coil (perturbation on the pulse shape) as the rotor moves which might be "seen" by by an intelligent monitoring system.

jack
998  Using Arduino / General Electronics / Re: Measuring current on: March 20, 2011, 11:20:15 am
I think you might find a hall effect sensor meets your needs.  These can measure both AC and DC  current and give a DC voltage output which is proportional to the current.  In effect your arduino would be reading a simple DC analogue input as frequently (or infrequently) as you desire.

http://sensing.honeywell.com/index.cfm?Ntt=csla&x=9&y=11&Ntk=si_all_products&ci_id=154286&la_id=1
gives you a starting point.  Generally these require around 12 volts DC to excite them and give an output signal of around 50mV per amp.

jack
999  Using Arduino / General Electronics / Re: Overheating on: March 16, 2011, 03:31:11 am
Simply because what's left inside the casing after overheating isn't what was put in to do the job.  ie they're cooked.  Consider it a bit like baking a cake.  Once it's been in the oven it is no longer eggs, flour, water etc
1000  Using Arduino / General Electronics / Re: Forward Voltage Drop on: March 16, 2011, 03:25:29 am
Because the LED is effectively a forward biased diode who's current is limited only by its own internal resistance.  IF the CR2032 could supply sufficient current the LED would self destruct.  As to the suggestion that the battery internal resistance will limit the current, that is so but is far from good design practice.
1001  Using Arduino / General Electronics / Re: Forward Voltage Drop on: March 15, 2011, 05:28:07 pm
Your CR2032 won't last long without some form of current limiting device; the simplest of which is a resistor in series with the LED.  I'd suggest you consider a 33ohm for a start point. 
If your multimeter fuse is blown and you really want to measure current you can do a "get-you-by" temporary fix by placing a piece of cooking foil around the fuse.  This offers NO protection to your meter so you do at your own risk.  In the good old days we used the foil liner from cigarette packets when such disgraceful practice was required.
1002  Using Arduino / General Electronics / Re: Transistors? on: March 15, 2011, 05:21:40 pm
The valves that Mike was referring to are what our colonial cousins on the west side of the pond would call a faucet

jack

1003  Using Arduino / Motors, Mechanics, and Power / Re: Building a Winch. Stepper motor or regular DC motor. on: March 15, 2011, 01:26:20 pm
If the two motors are pulling in the same direction then you could use a single motor by feeding the rope from the winch drum over a pulley assembly at the terminal location then run the rope back to the location of the winch where it can be anchored. 
1004  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 15, 2011, 07:15:44 am
If you want a low pressure "solenoid valve" then go for a motorised central heating zone valve.  These operate from mains AC but more importantly are readily available and reasonably cheap.  In fact you should be able to find one at your local scrap dealer for pennies.

Alternatively have you considered simply turning off the pump
1005  Using Arduino / General Electronics / Re: Electric water/pipe valve? on: March 15, 2011, 05:57:19 am
More information required :

a) temperature of water
b) pressure across valve when closed
c) flow rate through valve when open
d) power supply used to operate valve (low voltage 6/12/24DC or mains 110/230AC)

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