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1  Using Arduino / General Electronics / Re: High Voltage Regulation on: April 19, 2014, 07:05:42 pm
See the post : (Triac/Optocoupler Dimmer)
2  Using Arduino / General Electronics / Re: Not getting square wave output from SQW pin of DS1307 on: April 18, 2014, 02:32:24 am
On page 9 of the Maxim datasheet it shows the register which has the square wave enable bit that needs to be set.
3  Using Arduino / General Electronics / Re: Increasing RFID Read Range on: April 18, 2014, 02:27:38 am
Although I can't remember the make, I have seen RFID tags being read  off cattle at a range of 500mm to 1 metre. You might want to look at the websites of agricultural suppliers to see if any meet your range requirements and then see if you can find out whats in them.
4  Using Arduino / General Electronics / Re: Need a battery source on: April 18, 2014, 02:19:11 am
I have purchased about 20 of these cells from the likes of Ebay and Deal Extreme with mixed results. Thought that I was saving money. Reading various forums I discovered that there is no single Trustfire/Ultrafire supplier but the market is flooded with various Chinese backyarders who are shrinking the plastic *fire shells onto anything from recycled laptop batteries (the battery packs of many notebooks are filled with 18650 cells) to empty steel cans to micro batteries inside a 18650 casing. You just don't know who 'manufactured' your cells. You may order the same part number again next week but get cells from a different 'manufacturer'. Even within batches. See the links below:

They can be dangerous and are not value for money. I have since switched to Panasonic  and although they are labelled at 3100mah rather than 4000 or even 5000mah you see on *fires, you will actually get the 3100mah and a long life. And with less chance of explosion. They cost about $10 but are worth it. My supplier also offers nipple, flat top or tabbed cells at the same cost with the option of no protection circuit knocking a dollar off the price. The availability of such service also helps sort out the shonky suppliers.

5  Using Arduino / Programming Questions / Re: SPI.transfer, one byte or many? on: April 16, 2014, 04:08:11 am
Does this mean that SPI.transfer will only transfer one byte of an integer and not the whole integer (2 bytes) if it is passed as a parameter (as in the example on the Arduino website)?
6  Using Arduino / Programming Questions / SPI.transfer, one byte or many? on: April 16, 2014, 01:20:14 am
I'm having trouble with an SPI device so thought that I would go back to basics and check the reference.
However the Arduino website states "Transfers one byte over the SPI bus, both sending and receiving. " ( Then on it gives the following example:

void digitalPotWrite(int address, int value) {

The single SPI.transfer command is transferring two bytes (an integer). If I had a device that needed several parameters could I pass an array to the SPI.transfer and it would cycle through the elements?   
7  Using Arduino / Programming Questions / Re: Parsing through the individual digits of a double on: March 17, 2014, 04:49:52 am
  Which has given people who are doing stuff with gps no end of trouble, since apparently many of the calculations used really NEED the extra precision of "double."

I have just received one of these: (which I haven't connected up yet).
It does the NMEA parsing and geodetic (Haversine and crosstrack error) calculations to 64 bit precision, offloading the heavy lifting from the arduino.
8  Using Arduino / Programming Questions / Re: Parsing through the individual digits of a double on: March 16, 2014, 07:14:12 pm
Which GPS library are you using?
You state "The data is retrived via    int latitude =  GPS.latitude;  in the format: 4042.6142"
The type int cannot store a number with decimal places (i.e. the "4042.6142") without truncating it. You would need to use double however I would try to use a character array instead and look to use the strtok function to parse the string.
Try to stay away from the string class as past posts have shown problems with memory usage and bugs. If we can look up ythe output type(s) of the GPS library that you are using it will be easier to help.
9  Using Arduino / General Electronics / How to charge Supercapacitor? on: March 16, 2014, 07:00:38 pm
I want to use a supercapacitor to provide backup power to a DS3234 RTC.
I am stuck as how to charge the capacitor and then not have it discharge through the charge circuit when the power goes off.
The obvious solution would be a diode but even these have reverse leakage and the cap would only hold up for a few days.
Has anyone out there used a supercap with a RTC sucessfully? (I thought that this would be relatively common).
I found a couple of complex circuits using a couple of ICs and several passives but I was hoping to keep it  simple and small. 
10  Using Arduino / Networking, Protocols, and Devices / Re: SPI - change SS from pin 10 to pin 3 on: March 14, 2014, 11:01:03 pm
This thread goes into a fair bit of detail about changing SS from the default pin 10 for the ethernet library:
11  Using Arduino / General Electronics / Re: How to determine resistor value for current shunt? on: February 05, 2014, 07:17:07 pm
Thanks guys.
I think the current transformer is the way to go.
12  Using Arduino / General Electronics / How to determine resistor value for current shunt? on: February 05, 2014, 06:36:45 pm
I want to monitor the current going through each of three phases to a 415AC, 2 amp three phase motor.

This is to detect supply line loss of phase/brownout or a broken or shorted winding  in the motor.
I envisaged inserting a 0.1 ohm (or less) wirewound resistor into each phase of the supply to the motor and feeding the voltage across the resistor into a rectifier and buffer before reading it on the Arduino.

My question is, how do I determine the appropriate wattage rating for the resistor.  I thought that it must be different from working it out for a DC circuit.

13  Using Arduino / General Electronics / Re: Stainless steel soldering on: February 05, 2014, 06:21:12 pm
I get these ones from from Hobby King:

and while the tabs look like they are made from stainless, they are not. I have found that they solder but need a  bit of flux paste (in addition to the flux in the solder) and a fair bit of heat to make it flow. I assume that your batteries come from the same manufacturer as mine.

Be careful with the heat though as you can damage the battery. It may be worth clamping the leads close to the battery body with heamostats when you solder them to stop the heat running up into lithium and maybe starting a thermal runaway.
14  Using Arduino / Project Guidance / Re: RF communication between multiple devices on: January 21, 2014, 04:51:36 pm
With the Ebay units you can also use Mikes Virtual Wire library:
15  Using Arduino / Project Guidance / Re: RF communication between multiple devices on: January 21, 2014, 05:19:51 am
You could use these radios: or the more expensive breakout board

and the excellent library:

This library allows everything from unaddressed, unreliable messages to multi hop delivery with automatic route discovery and rediscovery (meshing).

I think Mike also has a library for the lower powered and less demanding RFM23.
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