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5866  Using Arduino / General Electronics / Re: 2 Wire temp readers? on: October 05, 2012, 08:29:17 am
Did you try measuring the resistance with a multimeter?   Some temperature probes are indeed thermistors, some are thermocouples, some are diodes and some are a whole chip.
5867  Using Arduino / General Electronics / Re: Transistor Question - Gate threshold voltage not providing max flow? on: October 05, 2012, 08:27:37 am
Depletion-mode power MOSFETs are as rare as hen's teeth - never seen a circuit using one, counts as highly exotic to me.
(Depletion-mode RF signal MOSFETs are another matter)

Show me a high-speed power switching circuit using a source-follower then?  Again must be very niche.
5868  Using Arduino / General Electronics / Re: Problem dimming filament displays vs. LED displays on: October 05, 2012, 08:10:36 am
The SPI hardware clocks upto system clock / 2, = 8MHz.  There is some code-overhead per byte of course but you can get to over 4Mb/s in practice.
5869  Using Arduino / General Electronics / Re: Powering Entire Arduino Mega with 3V3 on: October 05, 2012, 07:56:49 am
The Seeed Studios guys have a Mega-alike board with 5.0/3.3 switchable Vcc:
5870  Using Arduino / General Electronics / Re: Arduino Uno only putting out 1.5 volts from digital outputs instead of 5 volts on: October 05, 2012, 07:52:07 am
We are told there is a motor shield, the output pins are driving that.

We are also told the motor demo works.

My suspicion is something to do with the supply voltage or common grounding is awry - a schematic of the wiring might be useful, but I'd suggest checking that all the supply voltages are correct during operation and all grounds are common.
5871  Using Arduino / General Electronics / Re: Transistor Question - Gate threshold voltage not providing max flow? on: October 05, 2012, 07:48:00 am
The threshold voltage is the voltage at which the device turns off, not on. More specifically it is usually quoted at a few 100 _micro_amps.  Ignore Vthr completely for switching applications, the way it works is this:

If Vgs = 0V the device is off.

If Vgs > Vgs(on), then it is fully on, where Vgs(on) is the value quoted in the datasheet under the Rds(on) entry.

The datasheet tells you the on-resistance for a given Vgs - any voltage less than that is not guaranteed to turn it as fully on (or at all).

Logic-level MOSFETs will have something like "Rds(on) = ... (Vgs=4.5V)".  This means the on-resistance is guaranteed for logic level drive.
Non-logic level MOSFETs only have Rds(on) quoted for  Vgs=10V.

Sometimes values for Rds(on) are given for both 4.5V and 10V, this is a logic-level device basically.

Typical values for Vthr are much less than Vgs(on), about 1/4 of it in fact.  There is another voltage, the plateau voltage, at which most of the current switching happens - this is somewhere between Vthr and Vgs(on).  Datasheets have a graph of typical gate charge v. gate voltage - have a look at it and see the plateau.  If you provide a Vgs thats too low you may fall below the plateau voltage and the device will conduct only a small fraction of its rated current.

You only ever use common-source circuit configuration for switching in practice.
5872  Using Arduino / Programming Questions / Re: Conditional compilation fails on: October 05, 2012, 07:34:51 am
The way the pre-processing and compiling of sketches works is rather strange and fussy - I believe (but only based on a few issues I've had) that you should place all typedefs in a header file, not in the .ino - you don't say where those code snippets are, but I'd suggest moving them to a mytypes.h or similar header file in your sketch and #include that.
5873  Using Arduino / Programming Questions / Re: Frequency and Duty Cycle quesitons on: October 04, 2012, 06:51:00 pm
If for some reason you do want to program it yourself, you could start by reading the code for the Servo library and the datasheet for the ATmega328 (sections on timers).
5874  Using Arduino / General Electronics / Re: Problem dimming filament displays vs. LED displays on: October 04, 2012, 06:45:27 pm
Or you could directly PWM the outputs themselves

That would require tremendous amount of data being sent over the spi. I would say that's practically no-workable.

In that case (hc164 for example), the OP's original solution is better. Then it runs into the cross-conduction problem.

With hardware SPI at full speed (8MHz) its certainly fast enough to work, but I wasn't being that serious!
5875  Using Arduino / Audio / Re: Sound Triangulation with 3 Microphones on: October 04, 2012, 06:38:38 pm
With no information on your circuitry there's no way to judge where the analog noise might be coming from.

(check the attachment to the original post, for the wiring)

Well that (apparently) tells me only that you are using some sort of microphone module, not a microphone directly - is there information on that unit?

Secondly you seem to be running logic signals well away from the ground connection - all logic signals (being super-fast) ought ideally to run close to a ground line to keep stray inductance under control and to provide a return-path for the transients (otherwise you force that return path to be any near-by wire) - bundle the power supply and signal wires to the Xbee together for instance.  And keep them fairly short.
5876  Using Arduino / General Electronics / Re: Rotary Switch--5 Position? on: October 04, 2012, 06:27:32 pm
You used to be able to get rotary switches with 12 detents and configurable end-stops.  The one-pole version could do 2 to 11 way with the stop in place, or 12 way with no end stop.  2-pole 6-way and 3-pole 4-way variants were available, probably 4-pole 3-way too.
5877  Using Arduino / General Electronics / Re: Protecting PCBs against tarnishing - on the cheap? on: October 04, 2012, 06:24:13 pm
On the contrary a lacquer coating will protect against dirt and grime building up (which in humid conditions will conduct).

In normal conditions its not critical in the short term - avoiding fingerprints will prevent the most obvious tarnishing.

BTW tinning the board is not the best solution.  The reason is tin-whiskers.  This is one reason solder-resist is routinely used I believe.
5878  Using Arduino / General Electronics / Re: 2v output on arduino on: October 04, 2012, 06:12:00 pm
The built-in pull-ups are spec'd as between 20k and 50k, the relay is alleged to be 320 ohms, there's no way that makes a potential divider of 40%!

If the load on the pin is really 320 ohms then the chip is fried since it would produce about 4.5V into that load.

A good measurement to make would be the current into the relay winding when directly connected to 5V supply.  If it reads about 15mA then it is 320 ohms and the output pin is blown (assuming no other load on the pin). 
5879  Using Arduino / Programming Questions / Re: Unwanted shut down of outputs. on: October 04, 2012, 06:05:34 pm
The code does debouncing with a delay of 10ms, but then uses the button state to set the LEDs directly, so they will only be on with the button is pressed (and upto 10ms afterwards due to the debounce delay).

You want the button being active to toggle the state, something like
  if (val != buttonState)
    buttonState = val ;
    if (!val)  // button was pressed
      ledState = !ledState ; // toggle
    digitalWrite(LED1, ledState);
    digitalWrite(LED2, ledState);
    digitalWrite(LED3, ledState);
    digitalWrite(LED4, ledState);
    digitalWrite(LED5, ledState);

Using an array of pin numbers will make the code less voluminous!
5880  Using Arduino / Sensors / Re: Suggestions for accelerometers, gyroscopes, and GPS receivers? on: October 04, 2012, 05:53:01 pm
Well there are modules which combine I2C accel's and gyro's on eBay that are cheap and seem fine (I've an LSM330 one like this:  They may be 3.3V or 5.0V but not a big problem with I2C if you don't mix voltages on the I2C bus.

There are also 9DOF modules (accel/gyro/magnetometer) which might be worth considering (GPS can only give direction once moving).

GPS receivers - probably any modern module will be OK for outdoor use - look for cheap and the voltage you'd prefer (and whether you want separate antenna or integral).
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