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5791  Using Arduino / Project Guidance / Re: Lots of IO ? on: October 17, 2012, 09:55:59 am
For the seven 220 V/0.5 A outputs you don't even need relays.  Since the current is only going to be about 0.5 A, a MOSFET rated for 250 V would suffice...
MOSFETs don't work with AC.  (You could do it with a pair of complementary MOSFETs on each output, but would get "messy".)    Plus, he needs some "safety" isolation between the 220V and the Arduino.


Opto-triacs are one route for AC - find a nice mains-rated board with relays and/or opto-triacs to use.  And remember 0.5A inductive is completely different from 0.5A resistive as far as loads go.  6A or 10A rated relays are likely to both be up to the job and last a lifetime.
5792  Using Arduino / Project Guidance / Re: Standalone Stabilized Gimbal on: October 17, 2012, 09:51:29 am
I don't know about the Ardupilot software but its worth having a look at - there are various IMU frameworks out there I believe.

As for a small board - Pro Mini (can even go to 3V3 with the 8MHz version, reducing parts count if IMU is 3V3).  However motor driver is likely to want more volts anyway - stacking a standard motor shield on an Uno is simple at least.  There may be a simple IMU shield out there too.  For miniaturization have a look at, probably have some small motor controllers.
5793  Using Arduino / Sensors / Re: Sensing the impact of a projectile on: October 17, 2012, 05:53:24 am
Piezo sensor on base of target to detect impact?
5794  Using Arduino / Programming Questions / Re: Using Globals or Passing Parameters to a Function on: October 17, 2012, 05:27:16 am
Well global state is usually a mistake - as soon as you want more than one touchscreen you'll see why (!)

But you don't want to clutter up each call with such parameters.

So the answer is to provide a class for handling the menus, and the parameters then become instance-variables in the class. (Or to use C++'s  nomenclature "private member variables" I think)
5795  Using Arduino / Programming Questions / Re: Programming the timer/counter(s) on: October 17, 2012, 05:22:08 am
Or put another way:  yes you can update a TCNTn register on the fly, but it can be tricky to get this right (because for some counters its a 16 bit register and such updates take more than one instruction and the counter is still counting under your feet).

And of course it affects the current counting, its the count register!
5796  Using Arduino / General Electronics / Re: Help with drum machine schematic on: October 17, 2012, 05:15:19 am
You could try powering it with +/- 5V rails.  The Arduino will take more current from +4.5V than the splitter chip can provide I think.

Alternatively power Arduino separately, the 0.5V difference shouldn't matter because the circuits controlled have resistors that will limit the current, some have diodes as well which will lose 0.6V or so anyway.

It ought to be possible to redesign the circuit using rail-to-rail opamps to just run off 0..5V, but that's a lot more ambitious.
5797  Using Arduino / General Electronics / Re: Problem with IR receiver diode SEN-10266 on: October 17, 2012, 05:10:15 am
compact fluorescent lights in particular?
5798  Using Arduino / General Electronics / Re: MOSFET use for driving larger current devices on: October 17, 2012, 05:06:15 am
Basically yes - be sure it's a logic-level MOSFET (that can be switched with 5V logic - most require 10V).  The 5V fan might run a bit fast on 9V - so you are adding a resistor to drop the voltage a bit?  You would normally do that on the high side, and switch with a n-channel MOSFET or NPN transistor on the low side.

Is the fan a brushless motor BTW?
5799  Using Arduino / General Electronics / Re: Using transistors as switches.. problems on: October 16, 2012, 06:27:42 pm
That assumes the -15V side of the switch is supposed to go to 0V, whereas it might be that the 0V side will fall to -15V.

Also you would need an emitter resistor (which would protect the pin anyway) and would take signal up to +0.5V or so which might be an issue.
5800  Using Arduino / Programming Questions / Re: Checksums on: October 16, 2012, 06:23:04 pm
From the limited data this is probably trivial.
int checksum (char * str)
  byte sum = 0 ;
  char ch ;
  while ((ch = *str++) != 0)
    sum -= ch ;
  return sum ;
5801  Using Arduino / Programming Questions / Re: loss of precission on: October 16, 2012, 06:17:49 pm
It always helps to read the specification carefully - look for 'optional second parameter':
5802  Using Arduino / Sensors / Re: Strain Gauge to INA125 Troubles on: October 16, 2012, 06:15:02 pm
No!  The no-load voltage should be something that doesn't saturate the INA125, which if I recall the datasheet is 0.4V or more.  Not too much more or you'll lose useful range.  How about 0.5V as a compromise?

Having the amp saturated means it won't change at all until the input comes back into range.
5803  Using Arduino / Programming Questions / Re: loss of precission on: October 16, 2012, 06:08:55 pm
Please post the whole code - or at least something that compiles without error:
sketch_oct17a:6: error: ISO C++ forbids declaration of ‘convert’ with no type
5804  Using Arduino / Motors, Mechanics, and Power / Re: Stepper Motor Inconsistancies on: October 16, 2012, 05:52:19 pm
(Rotary) motors are rated in torque, not force.  You'll have to work out what torque you need given the geometry of the setup you have.
5805  Using Arduino / Motors, Mechanics, and Power / Re: Stepper Motor Inconsistancies on: October 16, 2012, 03:30:01 pm
The motor is rated to 3V 2A, but from what I've read on many forms/sites they should be run higher, 12 - 24V even.  Bad idea?

Hopeless idea.  The windings are 1.5 ohm and want 2A for full torque.  24V would mean 16A and a small explosion and fire.

Perhaps you are thinking about using a bipolar motor chopper drive, which provides constant current drive for a low-impedance motor from a high voltage supply?  In that case you'll need a driver that does this, such as the A4988, L6208 among many others.

This method allows much faster stepping since the whole voltage of the supply is available, if required, to overcome back-EMF.
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