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1  Using Arduino / General Electronics / Re: Question about voltage regulator to use on: October 01, 2013, 05:49:01 am
Rather than a LM7805, I would suggest that you consider a LDO regulator such as the LM2931.  In a car application, this will give you some immunity to the variability in the car's DC voltage.  The LM2931 is available in a SOT-263 package, or if you are not drawing too much current, a SOIC-8 package.
2  Using Arduino / Sensors / Re: (fixed) Using EEPROM in DS18B20 on: July 29, 2013, 05:34:00 am
Great find!
3  Using Arduino / Sensors / Re: Using EEPROM in DS18B20 on: July 28, 2013, 07:45:03 am
Post your entire code and let's see where that takes us.

Maybe someone will be able to spot the problem.
4  Using Arduino / Sensors / Re: Using EEPROM in DS18B20 on: July 28, 2013, 07:20:28 am
Make sure you are actually updating the scratchpad before copying it to EEPROM.  Write you TH, TL bytes (plus the config register - it is needed!) to the scratchpad.  Then read it back to confirm.  If it matches, go ahead and copy the SP to the EEPROM.

5  Using Arduino / Sensors / Re: Using EEPROM in DS18B20 on: July 28, 2013, 06:45:26 am
From the datasheet: "Data can also be reloaded from EEPROM to the scratchpad at any time using the Recall E2 [B8h] command."

Once you reload the scratchpad, then you can read the contents.

The same applies in reverse.  To write to EEPROM, load what you want into the scratchpad, then use the Copy Scratchpad [48h] to save the contents of the scratchpad into the EEPROM.

6  Using Arduino / Sensors / Re: Problem with more than 4 one wire temp probes on: June 05, 2013, 06:13:50 am
You might just be getting signal reflections.  Insert a 220 ohm resistor in series to each of your 2 red wires at the point where they connect to the Arduino.  That, theoretically, should eliminate the reflections.

A note on parastic powering: if you are not supplying 5V to the DS18B20, connect the VDD pin of them to Ground (yes, ground).  This is recommended practice from Dallas/Maxim - "VDD must be grounded for operation in parasite power mode."
7  Using Arduino / General Electronics / Re: How to connect a 1wire EEPROM with a pull-down resistor? on: June 04, 2013, 05:45:14 am
Not sure where you "heard" that 12 volt was required.  There is nothing in the data sheet about that.  Some older variants of 1-Wire EEPROM's needed the 12V to write to the memory, but the DS2433 does not.
8  Using Arduino / Sensors / Re: Where to get sensors for weather station? on: April 19, 2013, 05:34:11 am
If you want to go the 1-Wire route, try Hobby Boards (

9  Using Arduino / Sensors / Re: DS1302 Time set on: April 09, 2013, 05:08:56 am
Follow the code down and this line sets the time: 
  DS1302_clock_burst_write( (uint8_t *) &rtc);
10  Using Arduino / Displays / Re: Arduino HD44780 via I2C (PCF8574) on: April 09, 2013, 04:49:41 am
If your wiring is correct, it is possible that you might have the contrast set too high.  Back down the variable resistor until you see characters.

11  Using Arduino / General Electronics / Re: altitude detector on: April 05, 2013, 05:58:56 am
You might also want to look at the BMP085.  I've been using one very successfully to read altitude.  There's a tutorial located here:

12  Using Arduino / General Electronics / Re: Basic Transistor Question? on: March 24, 2013, 07:11:30 am
Not to over complicate things, but let's not forget to add a snubber diode across the fan to prevent back EMF from damaging the transistor.

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