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31  Using Arduino / Programming Questions / Re: Comparing whole arrays? on: July 23, 2014, 06:07:47 pm
Yes.  They will always be 4 cells.  A user is entering a 4-digit code and this code checks to see (after he enters in 4 digits on a keypad), if he entered in the correct code.

If the array lengths are known and equal, one call to memcmp() will do the job. If you are storing the passwords as null-terminated ascii strings (which would be a reasonable approach IMO) then you could also compare then using strcmp(). If the keypad is only used to enter decimal digits then you also have the option of converting the four digit keypad input sequence to a single integer number which you could then compare directly with ==.
32  Using Arduino / Programming Questions / Re: const int / int on: July 23, 2014, 12:25:01 pm
@KeithRB: AWOL's example is not really using a pointer. A true data item has an lvalue (an address where it lives in memory) and an rvalue (what is contained at that address). Simple assignment statements:

int a = 10;
int b;

b = a;

are rvalue to rvalue exchanges. The same is true in a function call:

That's not quite my understanding. An rvalue is something that can only be the right hand side of an assignment - it is a transient value. For example, (x+1) is an rvalue. An lvalue is something that can be the left hand side of an assignment - it refers to a variable or memory location. I know it's become much more complicated than that but I think the fundamental concepts of lvalue and rvalue are still the same.
33  Using Arduino / Project Guidance / Re: Video encoding decoding on: July 23, 2014, 12:04:41 pm
Since it's unlikely that the LCD would accept a format that exactly matches what the camera module produces, you should expect to do some format conversion between the two. How many bits per second will the camera be generating?
34  Using Arduino / Project Guidance / Re: Average two PWM signals on: July 23, 2014, 12:02:48 pm
   I THINK I want to process the signals which drive the ESC's

Since the Arducopter is generating the signals, it seems to me that the best approach would be to modify the Arducopter sketch to generate the output you want directly.

If you decide to go ahead with an external device instead, I suspect a servo mixer would do the job far better and far cheaper than an Arduino based solution, although an Arduino solution is definitely possible.

Finally, if you take the Arduino approach you would be dealing with a pair of servo control signals, not plain old pwm.
35  Using Arduino / Project Guidance / Re: Need storage advice for tools on: July 22, 2014, 11:23:46 am
I suggest you keep batteries separate from tools and wires etc.
36  Using Arduino / Project Guidance / Re: What is the problem with high frequencies in ADC conversion in Arduino Uno on: July 22, 2014, 09:48:17 am
With the prescaler factor 2, the ADC clock frequency is 8MHz and the sampling rate is 615 KHz. According to Nyquist criteria, the sampling rate should be greater than twice the input frequency. so with the 615 KHz sampling rate, 310 KHz was the maximum input frequency to b processed. But why we are not achiveing  this maximum input frequency signal to be processed. and why the arduino is not allowing to do the conversion(in time credentials), please provide me the proper reason and document.

I never got anywhere near 615 KHz conversion frequency. Even supposing you magically achieved it, and ignoring the fact that the results would be essentially noise, what is your Arduino going to do with each sample in the couple of dozen processor clock cycles it has available?  Bear in mind that just invoking an interrupt handler will probably take more than that. You can sensibly achieve a conversion frequency of a few tens of KHz, but even at that data rate you're going to have to be very careful how you process each sample in order to keep up with the data stream.
37  Using Arduino / Project Guidance / Re: How rugged is Arduino? on: July 21, 2014, 08:15:35 pm
This will be setup outside in a plastic box.

What range of temperature and humidity?
38  Using Arduino / Project Guidance / Re: Which Arduino for nRF24L01+ (3.3V issue) on: July 21, 2014, 07:59:00 pm
And what about the nRF24L01+ version with Transmit Power amplifier and Receive Preamplifier?  I guess that range is better but is it worth it ?(

I haven't used them, but comments from others confirms the range is massively increased and would certainly do everything you need. However, the power requirements and physical size are obviously both increased too which will make it harder to package.
39  Using Arduino / Project Guidance / Re: True "continuous rotation servo" on: July 21, 2014, 03:30:48 pm
You can add an external rotary encoder to almost any DC motor and/or gearbox. Some of them are designed to make this easy. For example I have a small DC motor with an integral epicyclic gearbox which has a stub shaft at the back to attach a rotary encoder. Using a conventional quadrature encoder and with a microcontroller providing positional feedback, this would produce something functionally equivalent to the NXT motor you mention.
40  Using Arduino / Project Guidance / Re: What's the best way to power arduino for long term remote use on: July 21, 2014, 03:15:40 pm
do you know if I can just cut the ends of a USB cable to make that cable?

Definitely not. If you need to pass data over a USB cable then one end needs to be connected into a USB host port and the other end needs to be connected into a USB slave port. You can't simple break out the wires from the USB cable and connect them to non-USB serial devices. If you want to connect a TTL async serial port to a USB port then you will need an adapter between then that presents a USB port on one side and a TTL async serial port on the other side. They're commonly available an inexpensive, the only thing to watch out for is that the TTL voltage of the adapter must match the TTL voltage level of the device it will connect to i.e. 3.3V or 5V for your Arduino.
41  Using Arduino / Project Guidance / Re: Server Watchdog - Reset PC/server if crashed on: July 21, 2014, 01:15:28 pm
I agree. But what about the simple idea of just passing the voltage through RAW pin instead of VCC pin? because there is a voltage regulator, regulating the voltage down to 3.3V?

I don't know what the specs say about the acceptable voltage range on the raw input. I wouldn't be surprised if it will run from 5V on the raw input, since 5V->3.3V conversion seems quite common on other Arduinos, but I wouldn't take that for granted unless you have seen it confirmed somewhere. Were you proposing to supply the 3.7V supply directly to Vcc or via the raw input? I don't know what the drop-out voltage is for the 3.3V voltage regulator, but I wouldn't be confident it'll run as low as 3.7V unless you've seen that confirmed. Is it safe to apply 3.7V to the Vcc pin of an 3.3V mini? It probably is, but again not something I'd want to assume.
42  Using Arduino / Project Guidance / Re: Dual axis tracker design on: July 21, 2014, 12:29:35 pm
every motor step it wil record the voltages in to the eprom mem , after the sweep it wil go to the strongest position found in memory ,  soem friend uses this for his solar pannel

Why save them in EEPROM? Surely it's the target position which needs to be persisted, not the instantaneous scan results. For a solar tracker where the answer is inherently changing, I don't see any reason to persist the answer either - after any reset you'd need to rescan anyway to find the new optimum. The scanning approach would also be inferior to using a pair of LDRs to tell you which direction to move towards the optimum, since that avoids needing to continuously hunt to find the optimum as it moves through the day.
43  Using Arduino / Project Guidance / Re: cmath library error uploading to arduino on: July 21, 2014, 12:25:46 pm
the issue was resolved after having the correct board and port selected. smiley

That always helps. smiley Glad you have resolved the issue.
44  Using Arduino / Project Guidance / Re: Server Watchdog - Reset PC/server if crashed on: July 21, 2014, 12:24:30 pm
You don't want to alter the logic voltage of your microprocessor while it's running, do you? I think that would lead to unpredictable behaviour.
45  Using Arduino / Project Guidance / Re: Interfacing with rope leak detector cable? on: July 21, 2014, 12:23:08 pm
I have no idea how they work, but my guess would be that it detects a conduction path between two electrodes when porous insulation between them becomes damp. You'd need to work out what sort of interface there was between the sensing cable and the control unit. If the sensor cable just plugs in directly I'd expect to find a change in resistance or capacitance of the cable when it was damp. If the cable includes any electronic components, you'd need to reverse engineer the output from that.
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