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1  Using Arduino / Project Guidance / Cheap wireless communication modules? (not necessarily Wi-Fi) on: February 23, 2014, 01:36:43 am
I'm trying to build a simple burglar alarm system. My design calls for a few wireless modules that will send a signal to a central Arduino when the sensors are tripped. I don't know what the best option for wireless communication is, in this scenario.

There will be about 5 of these modules, so they should be relatively cheap. Also, I imagine they would have to be able to communicate with the arduino simultaneously. Would RF modules be a good option?

I've read that Bluetooth modules can communicate simultaneously, but they are quite expensive.

As for Wi-Fi, I think it might be overkill and I have an vague hunch that it's probably not the best solution.  smiley-roll-blue
2  Using Arduino / Motors, Mechanics, and Power / Re: Understanding relay wiring (of a relay salvaged from a UPS) on: February 15, 2014, 05:22:25 am
why not?
By the way, I checked with a multi-meter. This is , indeed, how it is wired up.  smiley-slim
3  Using Arduino / Motors, Mechanics, and Power / Re: Understanding relay wiring (of a relay salvaged from a UPS) on: February 15, 2014, 12:38:01 am
oh.. Thanks Chagrin. That's a pretty good explanation.
4  Using Arduino / Motors, Mechanics, and Power / Re: Understanding relay wiring (of a relay salvaged from a UPS) on: February 14, 2014, 01:20:33 pm
I thought the wiring was "pointless" too.. I must have made some mistake in my interpretation in the connections. I'll check and post back. unfortunately, I can't find the data sheet for this relay. The only markings on it's outside say "LB1 DPNO" "Rayex Elec"
5  Using Arduino / Motors, Mechanics, and Power / Understanding relay wiring (of a relay salvaged from a UPS) on: February 14, 2014, 12:48:55 pm
Hello everyone.. it's been a long time since I last posted on these forums. smiley

Recently, I opened up an old UPS and found a mechanical relay inside. However, I can't understand how its terminal are connected.
The relay looks somewhat like this: http://www.seekic.com/uploadfile/member_product/18675/201112215424386.jpg
(I can't find an image or the datasheet for the exact model that I have)

On the circuit board on which this relay is mounted,  each one of the two terminals of the coil is connected to a terminal of the main power line. I have attached a diagram of the relay. Blue indicates the boundary of the package of the component and red shows the connections made on the circuit board. I think the +ve input is connected to T1, the negative input to T2 and the load accross T5 and T6. However, it seems that this layout does not isolate the coil circuit and the main power circuit. If so, what is the reason for wiring a relay like this?

6  Using Arduino / Project Guidance / Approaches to measuring power consumption on: July 09, 2013, 10:34:54 pm
I'm trying to build an arduino based power meter for a home.

Based on the research I've done, (mostly googling  smiley-wink ) I've seen that many designs use inductive current sensors. These are basically loops of wire that are placed around the wire carrying the current.

I would like to know if there are any other approaches to measuring current and which one is the best.
Having a low cost is a priority.
7  Using Arduino / Programming Questions / Re: Function to make arduino sample a sensor every 20 min on: March 23, 2012, 02:47:51 am
I only need to write the values to the EEPROM memory.
8  Using Arduino / Programming Questions / Function to make arduino sample a sensor every 20 min on: March 22, 2012, 04:38:57 am
What's the best way to make the arduino read an analog input pin every 20 minutes ? should I just use the delay() function?
9  Using Arduino / General Electronics / Re: What does the 1M resistor do in this circuit? (knock sensor) on: January 03, 2012, 03:04:15 am
If you have any diodes then put the 10K in series with the piezo, then to the arduino input. Then put a diode from input (cathode) to 5V (anode) and another from the input (anode) to ground (cathode).

GrumpyMike.. could you please post a schematic of that?
10  Using Arduino / General Electronics / Re: What does the 1M resistor do in this circuit? (knock sensor) on: December 30, 2011, 01:25:51 pm
Thanks for the quick reply...
but I still can't understand why a resistor has to be put in.. wouldn't that mean that the 'capacitor' would discharge? It seems that it would be desirable for all the charge to be sent in to the arduino (instead of passing to the other side of the "capacitor" through the resistor..)
11  Using Arduino / General Electronics / Re: What does the 1M resistor do in this circuit? (knock sensor) on: December 30, 2011, 01:03:47 pm
If you have any diodes then put the 10K in series with the piezo, then to the arduino input. Then put a diode from input (cathode) to 5V (anode) and another from the input (anode) to ground (cathode).
How does that work?
A series resistor might not add much protection, a piezo element is a close to ideal current/charge source in parallel with a capacitor. 
There aren't any caps in the circuit.. (do you mean parallel in the electrical sense?)
12  Using Arduino / General Electronics / What does the 1M resistor do in this circuit? (knock sensor) on: December 30, 2011, 10:12:47 am
Hi..
what does the 1M resistor do here? http://www.arduino.cc/en/Tutorial/KnockSensor

I don't have any 1M resistors at the moment.. would using a 10k resistor damage the arduino?
13  Using Arduino / Programming Questions / Re: Why doesn't this code work (stepper motor)? on: December 29, 2011, 12:24:50 pm
Yes..I modified the code to work with the two pin configuration..
14  Using Arduino / Programming Questions / Re: Why doesn't this code work (stepper motor)? on: December 27, 2011, 10:05:02 am
...well, i got the correct values.
for example,when i entered <24> I got 48 as the output..
15  Using Arduino / Programming Questions / Re: Why doesn't this code work (stepper motor)? on: December 27, 2011, 12:15:40 am
Sorry I wansn't able to reply sooner..

You're right.. I don't know why I put a "continue" statement in there.. maybe it was left over from some debugging.

As for the contents of the variables,
the inputs I gave were something like '<9>' or '<20>'. To check that "output" was an int, I tried multiplying it by 2 and printing the result out to serial. There weren't any errors, so I assume that means output is, in fact, and int.

If the extracted char array is really only 3 characters long, why are you using a String object?
I didn't really put much thought into selecting the type of varialbe..
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