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31  Using Arduino / Sensors / Re: ALPS EC11 rotary encoders... detents? on: August 17, 2014, 03:05:24 pm
For the Alps encoders I have used, the datasheet shows that the detent position is exactly aligned with one of the transitions. This is the exact opposite of what I want- the detent position needs to be stable. The Bourns encoders have the detent position midway between two transitions, which is far more sensible. So i never use Alps encoders, I always use Bourns.
32  Using Arduino / Programming Questions / Re: calling pinMode in the constructor on: August 17, 2014, 02:59:04 pm
and in particular it should not be trying to initialize the LCD in the constructor, because the power may not yet have stabilised and the LCD may not be ready.

There is a 50ms delay hanging out in there and a comment that goes with it that claims that it is for just that reason. 

50ms is an arbitrary value. If the begin() call is removed from the constructor, then the user can choose how much delay (if any) to use before calling begin().
33  Using Arduino / Programming Questions / Re: calling pinMode in the constructor on: August 17, 2014, 11:21:31 am
The LCD library is badly written. It should not be calling pinMode in the constructor, and in particular it should not be trying to initialize the LCD in the constructor, because the power may not yet have stabilised and the LCD may not be ready. I use a modified version of the LCD library in which the constructor does not call the begin method (and I have made a few other changes too).
34  Using Arduino / General Electronics / Re: How to get an output voltage of 9V from arduino uno?name some ic's for it. on: August 17, 2014, 11:17:18 am
You haven't said why you need 9V or what the application is, so we don't know how much current you need at 9V and it's hard to answer your question. But you are probably better off powering the Arduino with 9V to begin with, and then using a few extra components to get the Arduino to switch the 9V to whatever needs it.
35  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 05:47:30 am
so a beagle bone with 1GHz processor and having  32-bit timers won't help?what's the reason for that?

I may have been wrong. I see now that the processor used on the beaglebone has an ECAP unit. It's not completely clear to me what the maximum clock frequency of the ECAP unit is, but it may be high enough for your purposes. So if the beaglebone board brings out the ECAP pins from the chip to somewhere you can get at them, you may be in luck.
36  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 05:20:09 am
Having a beaglebone won't help, the issue is that you need a 200MHz+ counter with an input capture facility. FPGA is probably the best solution, but I can't help you with that.
37  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 05:01:36 am
PS - if what you are trying to do is to measure time of flight, then there are chips available to do this with resolution of a few 10s of picoseconds, such as the TDC-GP22 and MAX35101.
38  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 15, 2014, 04:53:11 am
The Duet master clock period is a little under 12ns, however the fastest clock that can be used for the timer/counters is half the master clock frequency.

To obtain a resolution of 5ns you will need to clock the counter at 200MHz or greater. I am not aware of any CMOS or TTL devices that can count this fast. So I think your only option may be to use emitter-coupled logic (ECL). I have only used ECL once, and that was many years ago. Looking at some datasheets, I think you could build a solution using about four 10E016 8-bit synchronous counters, some 10EL01 gates to link them together, some 10E131 D-flipflops to condition the input signal, 10E175 latches to latch the count, and some ECL to CMOS or TTL converters.

You might wish to google "Time to digital converter" for other possible solutions.
39  Using Arduino / Project Guidance / Re: Time Stamping on a NanoSecond Scale on: August 14, 2014, 02:14:23 pm
With what resolution and accuracy do you need to record the time stamps? Do you need to record the time of just the leading edge of the pulse, or just the trailing edge, or both edges?

If you only need to time stamp the leading edge, and resolution of 62.5ns is good enough, then you can use some simple electronics to extend the length of the pulse to (say) 1us, and then the input capture facility of timer 1 in an Arduino Uno or similar could be used to generate the time stamps.

Using an Arduino Due, I think you could get a resolution of about 24ns using a similar technique. To get a higher resolution than that, you would need to use an external high speed counter and latch.
40  Using Arduino / Project Guidance / Re: Standalone atmega328p-pu on: August 14, 2014, 06:55:37 am
I have seen a similar problem reported and least twice before on this forum, and in both cases the reason for it not working with the caps was that the caps were not really 22pF, they were something much larger like 22nF.
41  Using Arduino / General Electronics / Re: MC34063 buck with large variable input? help on: August 13, 2014, 02:47:20 pm
If you design for the highest input voltage, then the design should be OK at lower voltages too. If you design for a lower input voltage, then you may choose an inductor with a value that is a little too low at higher voltages.
42  Using Arduino / General Electronics / Re: Ir led low range on: August 13, 2014, 11:53:58 am
IR LEDs from remotes have quite a wide beam angle and work at quite a low power, so the range won't be very good. To increase range, you could use IR LEDs with a narrower beam angle and/or higher power output.

See http://uk.farnell.com/infrared-emitters for a selection of IR LEDs. The higher the value in the Radiant Intensity column, the more range you will get - but you also need to consider the value in the Viewing Angle column to see how accurately you need to point the IR emitter at the aircraft to get that range.

Bear in mind that the radiant intensity you need increases as the square of the range. IR control is typically used only for very short range models. It can also be swamped by sunlight, so it works best indoors.
43  Using Arduino / General Electronics / Re: Arduino Due: Minimum reading of "20" on analog inputs on some PCBs on: August 12, 2014, 04:54:11 pm
I have personal experience of this, because the SAM3X chip is also used in the Duet controller board for the Ormerod 3D printer, which I contribute towards firmware for. The SAM3X chip unfortunately has horrendous ADC gain and offset error tolerances. These errors can be up to about 64LSB in 12-bit mode according to the datasheet, far worse than the atmega series processors used on other Arduinos.

To calibrate the ADC you need to have 2 known voltages available. One should be close to but slightly above ground, the other should be close to but slightly below the analog reference. You can provide these voltages using a 3-resistor voltage divider. It's no use calibrating at ground and at Vref, because the linear range of some of these chips doesn't quite extend that far.
44  Using Arduino / Programming Questions / Re: Need Arduino to be Faster. on: August 07, 2014, 05:42:47 pm
You are reading all the sensors in sequence, one at a time. It would be quicker to read them all in parallel. To do this, you will have to understand how the CapacitiveSense library works, then modify it to read all 11 sensors in the same loop, with just one timeout for all of them.
45  Using Arduino / Sensors / Re: Interrupt problem with hall effect sensor on: July 10, 2014, 04:29:58 pm
When using a LM393 or other comparator to convert an analog input signal to a digital one, you almost always need to add hysteresis (positive feedback) to get clean digital transitions on the output. Digital Hall sensors don't need to be used with a comparator, and they have hysteresis built-in.
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