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631  Using Arduino / Project Guidance / Re: Measuring the weight of a beehive on: July 09, 2012, 01:44:55 pm
Whatever method you use you could also produce a dummy beehive (to act as a reference weight) using the same type of sensor.  Then as the reference weight changes with the temperature, humidity, rain, wind, etc your dummy beehive's measured weight can be used to compensate your actual weight measurements.

632  Using Arduino / Project Guidance / Re: HV supply ideas on: July 09, 2012, 11:58:53 am
Change the word "brave" to what you really mean  ie  STUPID

No offence intended but take it if you must

You obviously don't know what you're doing or dealing with so please accept the advice already given.
633  Using Arduino / Project Guidance / Re: HV supply ideas on: July 08, 2012, 04:46:59 pm
Goole TESLA COIL and you'll find what you are looking for - but controlling from 0 to 50kV is pushing the frontiers of science.

634  Using Arduino / General Electronics / Re: New Female DC power adapter does not work (has screw block terminals) on: July 08, 2012, 11:40:42 am
Did you remove several millimetres of insulation from the wire ends before you fitted them into the screw connector block ??
635  Using Arduino / General Electronics / Re: Stripping electronic equipment on: July 06, 2012, 03:22:25 pm
50 years ago I used to do this and ended up with piles of junk that was never used.  Now, I wouldn't give it the time of day unless there was a particular component that I required.  Having said that, I still take things to pieces and collect components just in case they might be useful - and periodically I throw out the complete collection in acknowledgement of its uselessness.
636  Using Arduino / Project Guidance / Re: Wha tdo I need to control a car's heater fan blower motor? PWM? on: July 06, 2012, 07:51:57 am
300watt fan in a car - what type of space vehicle is that ?  Mains powered domestic units are only 10s of watts.  I suspect you may be looking at an electric heater.

The only way you are going to answer your noise concerns with a "scrap" motor is to suck it and see.

There's plenty of links available on this site about driving DC motors - feed the search animal
637  Using Arduino / Project Guidance / Re: Soldering wire issue (not "stick") on: July 06, 2012, 07:47:48 am
If it's copper it doesn't matter whether its solid or stranded.  The main advantage of stranded is that the wire is more flexible; the surface area being exposed to the solder is greater but that's irrelevant if the joint is properly made.  Solder doesn't "stick" it "alloys" into the parent metal forming an interface compound which is a mix of both. 
638  Using Arduino / Project Guidance / Re: Soldering wire issue (not "stick") on: July 05, 2012, 04:36:11 pm
sounds like your cable has aluminium cores.  That being the case it's going to be VERY difficult (ie virtually impossible) to get a soldered joint.
639  Using Arduino / General Electronics / Re: Transformer vs Capacitor voltage divider on: July 05, 2012, 12:59:47 pm
The circuit you show is not a voltage divider. It is using the capacitor as one might use a series resistor to drop line voltage.  Since the current through a capacitor is out of phase with the voltage across it (by 90 degrees in the ideal situation) the heat or wattage generated is zero. This technique is widely used in low current demand systems. 

Since there is no effective isolation from the mains voltage this concept should NEVER be considered where there is ANY possibility of personal contact with ANY of the device components.  Therefore is should NEVER be considered as a means of providing a "wallwart" type power supply.

The capacitor used should also be rated for the service duty - usually specified as having class X insulation.

The reactance (capacitive resistance) is frequency dependant and is specified as Xc = 1/[ 2.Pi.F.C] where F = frequency and C= capacitor value in farads. 
640  Using Arduino / General Electronics / Re: Relays or Transistors? on: July 04, 2012, 03:38:24 pm
I'm not sure there is a "cheaper" way that would be suitably reliable.  However you might want to consider the following :-

There maybe the possibility you could "strobe" each of the 6 numerals in turn for which you'll need 6 SSRs. (relays cannot be strobed at high speed) Each SSR permits power to the relevant numeral when it is to be considered "active"

Then you would need 7 SSRs to drive each segment of the numeral array (again relays would be unsuitable) All similar numeral segments can be driven by a single common source since it is the previously mentioned "strobe" SSR which determines which numeral is illuminated.

So, a total of 13 SSRs and a whole lot of software to perform the strobing.

Assuming each numeral is strobed in turn that means a maximum turn-on duty time of only 16.6% of a complete strobe cycle.  You will/may need a little space between each strobe to achieve the switching so perhaps a maximum of say 15% duty cycle.  At such a low duty cycle you may experience flicker.

Given a choice I'd go for the simpler but more expensive relay system.

Alternatively you might want to use a "flip-flag" concept as used on railway and airport notice boards, whereby bright white letter segments are made visible as required.  These could be strobed and latched as required using only 13 relays.  If you need them "bright" then make them reflective and shine fixed bright lights onto them.
641  Using Arduino / General Electronics / Re: Using a PCB transformer on: July 04, 2012, 01:47:43 pm
Cyclegadget

You missed the point I made  -  the user is UK based where ALL appliance leads (other than botched illegal ones) have a fuse built into the plug.  They can be a pain in the butt when it comes to size (they are large) but at least it gives a relatively fool-proof system (apart fro having too high a rated fuse for the cable in use).

If your mains sockets can pump 20 to 100 amps or so into an appliance lead, what protects your normal small domestic appliances that have mains leads suitable for carrying only a couple of amps.
642  Using Arduino / General Electronics / Re: Relays or Transistors? on: July 04, 2012, 01:40:57 pm
On balance (cost, safety, reliability etc) I'd suggest you go for 6 off 8-way relay boards.  You need 7 switches per numeral so the 8-way boards fit the bill and give you one spare relay should you need a decimal point.  These are available off-the-shelf from arduino system suppliers and suitably rated and designed for switching mains voltages
643  Using Arduino / General Electronics / Re: Relayshield Question on: July 04, 2012, 11:34:25 am
In answer to the basic question, relay data sheets for that type of relay suggests somewhere around 0.4 watts to drive the relay coil.  Considering that you have bought the 5 volt version, that implies each relay will require around 80mA to drive it. (0.4/5), times 8 for all relays being energised, equals 640mA at least.    That being the case, and presuming you want to use this board, I'd suggest you couple a 5 volt regulator (with heatsink - it will get hot since it will be required to dissipate around 5 watts) to say a 12 volt supply and feed the relay board power from this source.
644  Using Arduino / Motors, Mechanics, and Power / Re: Do DC motors "mind" being PWM'd.... on: July 04, 2012, 07:45:37 am
A DC motor shouldn't "mind" a PWM supply.  When you think about it, the rotor windings are switched in and out of circuit on a continuous basis by the commutator as the motor operates.  So switching the supply on and off via PWM is very much the same operation.

As others have said, using a rheostat to control speed is both wasteful of power and poor speed control.  Assuming a preset rheostat value, as the motor load increases, the current increases, so the voltage loss across the rheostat increases.  This leaves less voltage to the motor terminals so the motor tends to slow down. (Motor speed is proportional to voltage)

On the basis that PWM voltage is averaged out, then motor speed is effectively proportional to PWM duty, irrespective of shaft load
645  Using Arduino / General Electronics / Re: Using a PCB transformer on: July 04, 2012, 03:26:56 am
In my opinion a fuse on the primary is a waste of time and a failing to understand why the fuse is there.  The principle of a fuse is to protect  and the only device on the primary side that requires protection is the supply lead from the mains to the transformer.  Since you are UK based you are obviously using a 3-pin fused plug.  The fuse in the plug protects the supply line and in your case should be rated for 3 amps.

A fuse on the secondary protects the transformer secondary windings from a "downstream" fault and that is where the only fuse that is required should be located.
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