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5761  Using Arduino / Programming Questions / Re: input/output question from Newbee on: October 17, 2012, 10:25:52 am
More information about the sensor and load would be helpful...
5762  Using Arduino / Programming Questions / Re: What's PROGMEM for? on: October 17, 2012, 10:23:48 am
The 328 microcontroller has 32k of flash memory, 1k of EEPROM and 2k of RAM.  For read-only data you have the option of putting it in the flash memory (which is effectively read-only except when uploading a program) to save space in RAM.  PROGMEM is the compiler directive to say "put this data in flash, not RAM".

Note that flash memory _can_ be written, but only a page at a time, and its slow.
5763  Using Arduino / Project Guidance / Re: Measuring solar panel voltage on: October 17, 2012, 10:16:55 am

A Solar Cell is a current source , and will produce 0.5 V per cell even with only a low light level.
So a Solar panel , even in a relatively low light environment will produce close to its full voltage.

Ever measured a solar cell?

Indoors 0.7m from lamp: 0.27V
indoors near window: 0.37V
Outdoors in shade of bush: 0.47V
Outdoors in weak sun (breaking through clouds): 0.515V

A PV cell is not a current source.  Its a current source in parallel with a forward biased semiconductor diode(*).  When you measure the open-circuit voltage you are measuring the diode voltage with the current all flowing through the diode rather than external circuit, so it obeys a logarithmic law against light-flux.

(*) approximately.
5764  Using Arduino / Project Guidance / Re: Is JFET same as a FET Op amp? on: October 17, 2012, 10:01:12 am
I am using it to amplify a circuit that reads a tiny voltage from a pH probe.
Tiny means many things - how tiny?
5765  Using Arduino / Project Guidance / Re: Any way for a servo or stepper to hold/lock position with power off? on: October 17, 2012, 09:59:52 am
Or, if you can find one, an electromagnetic clutch/brake that is engaged on power-off.
5766  Using Arduino / Project Guidance / Re: send commands by sms on: October 17, 2012, 09:57:17 am
5767  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.
5768  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.
5769  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?
5770  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)
5771  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!
5772  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.
5773  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?
5774  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?
5775  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.
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