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1876  Using Arduino / Motors, Mechanics, and Power / Re: Servers,Server Rack, Temperature on: October 27, 2012, 10:07:27 pm
Thanks for the information sir. This helps me a lot.
In our school the server rack are close  but not all. Do you have any idea about the temperature range?

Not sure whether you mean close or closed, but I'd be very surprised that even if there is a solid glass front door on the cabinet, the back will be open or nearly so. Often the cooling air is brought in from below with a false-floor arrangement. Proper racks will be designed to facilitate proper airflow even when they are right next to each other. There may be specs on aisle space.

I do not know any temperature ranges, I will again have to direct you to the equipment manufacturer. There may be some standard, or if not a formal standard, then a typical industry rule of thumb. I've spent a fair amount of time in data centers, usually knew the environmental guys but did not get into that part myself. It can get pretty involved, measuring, adjusting temperatures and airflows. I wouldn't be surprised if the racks have specifications regarding airflow (CFM) and maximum heat (BTUs) that can be exhausted. Equipment specs should also include BTUs.
1877  Using Arduino / Motors, Mechanics, and Power / Re: Servers,Server Rack, Temperature on: October 27, 2012, 09:41:32 pm
I would consult the specifications for the particular server(s) being used. But I doubt they will differentiate between "server room temperature" and "server rack temperature". Most racks are very open, the idea being that the air available to the racked equipment is essentially the same as the room air.

Equipment manufacturers will usually just specify a single ambient temperature, which is assumed to be the temperature of the air being drawn into the equipment.

Not sure what you are trying to accomplish, but most modern equipment made in the last decade or two has built-in temperature sensors which are read by various management software that can automatically raise an alert if something is running hot.
1878  Using Arduino / Microcontrollers / Re: ATTiny85 run at 1Mhz When I Program "delay(1000)" does not give 1 second? on: October 27, 2012, 06:08:18 pm
Thanks both Fuses must have been wrong Fungus was right all along
Bootloaded 8Mhz to chip then loaded program and delay is now right .

Good deal!

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I just wondered Jack is there any power usage difference between running at 8 and 1 Mhz ?

Yes, generally, the slower the clock, the lower the power consumption. See Figs 22-2 through 22-4 in the datasheet. If my well-calibrated eyeball serves, at 3V, 0.6mA at 1MHz vs. 2.8mA at 8MHz.
1879  Using Arduino / Networking, Protocols, and Devices / Re: Wireless sensor network on: October 27, 2012, 05:15:49 pm
This can be done reasonably well with XBee ZBs (S2) in API mode. After a module completes a transmission request, it sends a TX Status frame which indicates success or failure of the transmission.

I think the XBee 802.15.4 (S1) modules operate very similarly, but I've only used this with S2.

Not sure why it's important to you, but for short payloads, I typically see 25-30ms if just a single hop is involved.
1880  Using Arduino / Project Guidance / Re: Multiple XBee modules on: October 27, 2012, 04:35:56 pm
PaulS is correct, using separate PAN IDs effectively creates different networks that will not interfere with each other. There is no cause for concern whatsoever.

But, if it were me, and assuming the controlling is all done from one point, I'd consider five XBee ZBs, one being the controller and the other four connected to the controlled devices. Could save $50 or so that way.
1881  Using Arduino / Project Guidance / Re: Water level probes with minimal componant count? on: October 27, 2012, 04:28:56 pm
What is the input impedance of an analog pin? High, yes? Tens or hundreds of megohms? Given that, how big an issue is electrolysis?

I have a project that is similar to the rain or leak detector in that the probes are always dry unless there is a problem. I sample the probes once per second (which is a fair amount of overkill), but only turn the sense voltage on for a few milliseconds. Plus the probes are stainless steel. So I didn't worry about electrolysis at all.
1882  Using Arduino / Microcontrollers / Re: ATTiny85 run at 1Mhz When I Program "delay(1000)" does not give 1 second? on: October 27, 2012, 04:11:21 pm
Like a lot of AVR MCUs, the ATtiny85 comes from the factory set so that the system clock is provided by the 8MHz internal RC oscillator, and the prescaler is set to divide by 8, so the actual system clock frequency is 1MHz.

When a sketch is compiled, the compiler needs to be told what speed the hardware is set to, in order to provide accurate delays, etc. This is done via the f_cpu parameter in the boards.txt file.

To change the clock speed, the MCU fuse bytes need to be re-programmed. See the datasheet for details.

The appropriate fuse byte values to match f_cpu are also specified in boards.txt (low_fuses, high_fuses, extended_fuses).

By issuing a "burn bootloader" command, the fuse values for the selected board are burned to the MCU. Note in this case "burn bootloader" is a bit of a misnomer since there is no bootloader for a tiny85. (The "burn bootloader" command on an m328 would burn the bootloader as well as the fuse bytes.)

As long as the fuses burned in the MCU match the f_cpu for the selected boards.txt entry, delay(1000) should give a one-second delay with either a 1MHz or 8MHz system clock, so something is amiss here. Your symptoms could be explained if the fuses were set to provide an 8MHz clock, but a 1MHz board was selected in the IDE. Simply changing the board in the IDE does not alter the system clock frequency setting in the hardware. "Burn bootloader" will do that.
1883  Using Arduino / Networking, Protocols, and Devices / Re: Xbee on: October 27, 2012, 10:25:59 am
Jack,
here is the product,
https://www.sparkfun.com/products/9087

ok,this is a special product by Digi, and they do not make this anymore.

Actually that is an S3B part, and while that particular part number (XBP09-XCSIT-009) doesn't appear to be current (I don't find it on Digi's web sire), I think these are equivalent.

You say you're trying to use API mode, that could be an issue, according to the product manual, this series does AT mode only. There is a binary command mode, but it appears limited to reading and writing module parameters, not sending or receiving the actual live data. Not sure what doc you may be following to do the API interface, but whatever it is, I think that it is inappropriate for this particular XBee series.

I don't recall seeing any discussion on this forum related to S3 modules and I haven't worked with them at all, but as always, GIYF.
1884  Using Arduino / Programming Questions / Re: How to set time on DS1307 using Time library? on: October 27, 2012, 10:03:51 am
BTW I found this great and super simple code online that sets time just fine without any library:

While libraries are great because they simplify the mainline code, it's very much worthwhile to understand some of what's under the covers, in this case, using I2C to interface to the RTC chip directly. So if there is a problem, or a feature of the chip that the library doesn't implement, you can do it yourself. In the case of the DS1307RTC library, for example, it doesn't implement any methods to interface to the DS1307's static RAM.

Also note the layers of libraries here. DS1307RTC depends on both the Time library and the Wire library. The code from bildr only requires the Wire library. It could be taken one step further, and the ATmega328's registers could be manipulated directly to do the I2C communication, and then the Wire library could be eliminated.

Glad you got it working!

1885  Using Arduino / Networking, Protocols, and Devices / Re: Xbee on: October 26, 2012, 04:13:07 pm
well,i didnt make it up...we are a team of 2,and i wrote the code on my team-mates arduino, not mine, and tested it there,so i knew what happened,and i coudnt reply yesterday because i did not have the zigbees with me.,and coudnt call my team mate up at 5 in the morning. smiley-razz

Well, that's complicated! smiley-grin

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ok,so here is the deal now.
I made a mistake in the above posts,we do not have a xbee series 2, we have one called the xbee pro xsc ufl..now according to the internet , they have stopped manufacturing it .But we did configure them as a master and slave, now comes the problem, in x-ctu, no function set is actually working for it,it always fails,basically we are trying to use the API mode ,can you please explain me how to do it,i am really clue - less about it.

What is the part number on the bottom of the XBees? ufl would be the antenna connector. I don't recognize "xsc". XBee Pro can be either S1 (802.15.4) or S2 (ZB). So the first step here is to be certain of the hardware we are dealing with.
1886  Using Arduino / Storage / Re: EEPROM & magnetic field on: October 25, 2012, 09:00:17 pm
Nope, the chip is silicon, non-magnetic.
1887  Using Arduino / Programming Questions / Re: How to set time on DS1307 using Time library? on: October 25, 2012, 11:00:54 am
Hmmmm, that's odd, I wouldn't think you'd have to use their RTC kit either. I have several of their RTCs and they work fine with the Time.h and DS1307RTC.h libraries. I think I may have tried Ada's library in the past, and I don't remember any problems, but for whatever reason I just stick with Time.h and DS1307RTC.h. Time.h has a lot of functionality which I like. DS1307RTC.h also will work with a DS3231 (Chronodot).
1888  Using Arduino / Programming Questions / Re: How to set time on DS1307 using Time library? on: October 24, 2012, 09:41:18 pm
There is a second library that comes with the Time library, called DS1307RTC. Once the system time is set, all that is needed is a call to RTC.set():

Code:
#include <Time.h>
#include <DS1307RTC.h>
#include <Wire.h>
...
setTime(hr,min,sec,day,month,yr);
RTC.set(now());
1889  Using Arduino / Installation & Troubleshooting / Re: Blinking L LED on Uno. Can't get examples to work. on: October 24, 2012, 07:15:52 pm
Ummm, actually that sounds like all is working as designed.

the L LED blinks a fast a few times

That's the bootloader starting after the MCU is reset (three fast blinks)

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and then the TX and RX LEDs blink fast.

That's the sketch being uploaded.

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Then the L starts blinking again.

That's what the Blink sketch does. Blink turns the LED on for one second, then off for one second, ad infinitum.
1890  Using Arduino / Networking, Protocols, and Devices / Re: Xbee on: October 24, 2012, 07:06:47 pm
and i'd copy paste if i had the code written before.smiley-grin

I'm confused. How could the code have not been written? Were you making the symptoms up, the buffer business and all?
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