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31  Using Arduino / General Electronics / Re: how fast can the arduino switch a transistor? on: June 27, 2014, 06:19:32 am
Can you get a solenoid valve to open and close that fast ?
32  Using Arduino / Motors, Mechanics, and Power / Re: 3VAC on coil side of relay. What's going on? on: June 25, 2014, 03:58:38 am

You will get about 6V between the mains neutral and ground and you can use that voltage for free, it does not get metered. Although you will possibly get put in prison if the electricity company catch you doing it.

Come, come Mike you really shouldn't encourage this sort of behaviour.

If a neutral feeder fault (open circuit) occurs anywhere in the domestic distribution side between the substation and the home then the neutral line within the house could rise to line voltage.  Not a happy scene for anything using neutral-ground potential as a power supply.
33  Using Arduino / Motors, Mechanics, and Power / Re: Cheap power supply? on: June 22, 2014, 01:09:16 pm
On the basis that you have to plug your mains lead into a wall socket then why not buy a suitable wallwart which outputs 12volts (or whatever) and instal a suitable socket on your case for the wallwart DC lead to plug into.  That offers the advantage of solving your space problem and keeps the mains AC voltage away from your low voltage electronics.
34  Using Arduino / Motors, Mechanics, and Power / Re: Cheap power supply? on: June 22, 2014, 05:27:30 am
I'm not suggesting smps are junk, they are generally excellent at what they do; it's just that the one you have would appear to be.  If a device alters its output from the design DC voltage to a much higher AC one when you load it, then it is obviously of questionable use to power a microprocessor based system.  But at the end of the day, it's your choice.
35  Using Arduino / Motors, Mechanics, and Power / Re: Cheap power supply? on: June 22, 2014, 03:06:47 am
With a 400v rated capacitor onboard it is almost certain to be a switched mode power supply.  Your best bet is to cut your losses, throw the heap of junk away and buy a decent supply rated to do what you wish.
36  Using Arduino / General Electronics / Re: Measure High current on: June 21, 2014, 01:38:12 am
There are extreme dangers associated with what you intend since your measurement circuit is always attached electrically to the 1000v supply and the only advice I could give is AVOID doing so.  It matters little whether your supply is AC or DC, the potential is equally as dangerous.

Assuming one side of your 1000v supply is "grounded", the shunt should be on the grounded side of the supply to minimise the potential that your measurement system could rise to.  But if the supply polarity should be accidentally reversed, even momentarily then your measuring device voltage becomes lethal.   Similarly if the ground connection of your supply should become open circuit due to a wiring or operating fault, the measurement connection potential could rise to a lethal value.

If your 1000v supply is "floating' ie not connected to ground, (a common practice on DC systems) then both positive and negative terminals should run at about 500v with reference to ground, so again lethal.  If a ground fault develops the measuring side could be at either 0V or 1000v, it all depends on which pole develops the ground fault.

If you are already happy using hall sensors then stick with them.  There are no prizes for winning the Darwinian medal of natural selection.  ( The process whereby those who endeavour to kill themselves by doing idiotic things manage to do so before they get a chance to breed the next generation of like minded individuals)
37  Using Arduino / Motors, Mechanics, and Power / Re: Reading state of a 0-200VDC motor. on: June 19, 2014, 02:15:17 pm
If you can stick a piece of reflective tape onto a moving surface you could use an IR sensor unit to detect rotation.  No need for fancy encoder devices which are generally intended as position sensors.
38  Using Arduino / Motors, Mechanics, and Power / Re: Reading state of a 0-200VDC motor. on: June 19, 2014, 02:45:04 am
You only need
on/off information?
Thats right, i don't need to know how fast it's running, just is it running.

Do you mean  "it has voltage applied" or "it is drawing current" or "it is rotating"
I know it's being picky but they really are three different variables.
39  Using Arduino / General Electronics / Re: What LED colors have the same voltage and brightness? on: June 19, 2014, 02:39:30 am
To some extent "brightness" is also down to the perception of the viewer. 
40  Using Arduino / Motors, Mechanics, and Power / Re: How to power 16 channel relay on: June 18, 2014, 04:00:17 pm
The unit signal inputs drive directly from the arduino 5 volt signals (your linked web blurb says so).  Power for the relays and onboard components comes from your external 12 volt supply unit.
41  Using Arduino / General Electronics / Re: About BiPolar Power Supply on: June 18, 2014, 03:47:25 pm
Wow, a manic depressive power supply   smiley smiley

Sorry, it was too good to overlook.
42  Using Arduino / Motors, Mechanics, and Power / Re: Reading state of a 0-200VDC motor. on: June 17, 2014, 01:30:27 pm
Might I suggest a hall effect current transformer unit which monitors motor drive current.  These units are available with outputs of 5 volts DC at full range current.   This design also provides total isolation from the motor voltage.
43  Using Arduino / General Electronics / Re: making a potentiometer that has a low range of resistance?i on: June 16, 2014, 01:23:24 pm
Low resistance pots are normally called rheostats and are wire-wound (no use at RF).

Not so.

A rheostat is a variable resistor and generally needs only 2 terminals.  It provides no potential divider capability.  Certainly rheostats are generally of low resistance but that does not  mean low resistance potentiometers should be called rheostats.
Rheostats are generally linear devices but can be obtained with a nonlinear function.

A potentiometer (whatever its resistance value) has at least 3 terminals (some have a fourth fixed value terminal at mid scale 50%) and provide a potentiometric divider function.  Track resistance can be logarithmic, anti-logarithmic or linear.

Potentiometers can act as rheostats by using one end terminal and the slider terminal.  It is generally good practice to also connect the "unused" end resistance terminal to the slider.  This ensures there is always a resistance in circuit even if the slider contact goes open circuit.
44  Using Arduino / Motors, Mechanics, and Power / Re: Solenoid type on: June 13, 2014, 12:25:21 pm
Read my input  -  slug endeavours to reach a balanced position at the mid-point of the coil.
The position of the stop does affect the final pull value with it being zero at the point where the slug centre is at the coil centre.  In your illustration this will only occur if the slug is shorter than the coil
45  Using Arduino / General Electronics / Re: Help with math on circuit on: June 13, 2014, 12:21:13 pm
For a relay taking 30mA I'd drive it with a small transistor like a 2N2222. 

That 30mA is likely the holding current, the energizing (pull-down, activation( current could be much higher.

Best practice is simply to always use a driver (transistor, FET).  And, of course, that flyback diode!


If the relay was an AC device the pull in current would indeed be much higher than the holding current since Xl depends upon coil inductance which changes with armature position.  However as the relay is a DC device the coil current may be simply calculated from coil resistance.  If anything the inrush current will be less than the steady state value due to the coils self-inductance tending to inhibit current change.
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