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1  Using Arduino / Sensors / Re: BMP085 voltage on: August 23, 2011, 04:33:18 am
I had the same problem, with my main project's sensor suite... The bulk of the sensors were running on 5v and the BMP085 would only do 3.3v.

I ended up buying one of these ( to sort the problem out. I still need to get it connected and soldered into place, but the thread I started in the Communication part of this forum seems to suggest that it will do the job.

2  Using Arduino / Networking, Protocols, and Devices / Re: Two sensors on I2C bus, different voltages - How? on: August 17, 2011, 10:01:25 am
Thanks guys! It looks like that DSScircuits LLC is the thing that I need (or the Sparkfun one), I just hope that I can get one from someone in the UK.

Really appreciate your help, and I will let you know how it turns out!


No sign of that one in the UK, looks like the Sparkfun one from Cool Components will be getting purchased. Let's hope it is simple enough for me to work with!
3  Using Arduino / Networking, Protocols, and Devices / Re: Two sensors on I2C bus, different voltages - How? on: August 15, 2011, 02:35:20 pm
You guys are going to hate me for saying this, but your are talking a different language... Is there any chance someone could post a circuit diagram of how to do this that I could use to try and get this straight in my head?

The talking of pulling the bus to 3.3v and then powering the DS1307 with 5v sounds what I need, but I could do with pointers. Idiot pointers.
4  Using Arduino / Networking, Protocols, and Devices / Two sensors on I2C bus, different voltages - How? on: August 15, 2011, 11:19:45 am
I'm constructing a weather logger/display system for my office so that we can check to see if the A?C is working. It's using an Arduino Nano as the base, and has a number of components hanging off it (temperature, humidity, pressure, etc), as well as a microSD breakout board and a DS1307 RTC.

I've had all of the individual parts of the circuit working in isolation and mostly together, and the last attempt had everything bar the BMP085 pressure sensor breakout board connected; I'd previously had that working on its own on my Uno board. The code compiles and looks ok, but I have run into a problem with the DS1307 and the BMP085 in that, whilst they both run on the I2C bus (not a problem), they use different supply voltages.

How can I get round this problem and connect both devices to the I2C bus? I am guessing that I can't connect +3.3 to the BMP085 and +5 to the DS1307..

The closest link to the DS1307 breakout that I can find is here: I have asked for a more complete datasheet from the seller. The main datasheet for the Dallas IC is here:

The BMP085 breakout I bought was this one (sorry for the eBay link) and the datasheet is here:

I've tried to find documentation on doing this, but no joy so far, so I figured that the forum would be a good place to ask. If anyone can help, I'd appreciate it.

5  Using Arduino / Sensors / Re: Internal/external sensor project - Power recommendations on: January 29, 2011, 01:23:36 pm
Give me a chance... I'm at home and most of the kit is at work. I'm also a beer into my weekend, so it might take a while. smiley-cool
6  Using Arduino / Sensors / Re: Internal/external sensor project - Power recommendations on: January 29, 2011, 01:05:34 pm
*grin* Thanks Lefty!

I'm building that list as we speak, so you might have to wait a few minutes.

List so far:

DHT11 Temp/Humidity sensor on breakout board
DS18B20 Temperature sensor
DS1307 RTC on a breakout board
Arduino W5100 ethernet shield
PIR sensor - Dammit, will have to see what it is.
7  Using Arduino / Sensors / Re: Presence detection. on: January 29, 2011, 12:52:52 pm
Second vote for RIFD.

You could get one of the short range reader kits and hook it up into the car, then find the corresponding RFID token (the sort that look like fuses) and put it on your keychain. Failing that, if you have soe sort of RFID in your wallet already, you might be able to use that instead. The range might be too short for the HiD type readers/cards though.

I've often thought of using something similar as a sort of central locking for my house...
8  Using Arduino / Sensors / Internal/external sensor project - Power recommendations on: January 29, 2011, 12:41:59 pm
So, I'm starting on my first proper project with my Arduino, nothing fancy, just a bundle of sensors that will measure temperature and humidity inside and outside the house, log them all and put them on the internet (plus notify me of when the postman comes!), and I'm having problems with the power source for it. I only have a single power socket to work with, and it is likely that the power from the board itself will not be enough to power everything.

I've been advised to use a standalone 5v power supply for the sensor packages (An old Nokia charger will do 5v/890mA, handy), but the board itself, especially with the ethernet shield and SD card will chew up a 9v PP3 in short order, so I was thinking of giving it a 12v supply from another one of the many bits of kit I have around the house. Ideally though, I'd like to use a single power supply to do both the board and the sensor package, and remembered that USB delivers both 12v and 5v through the cable on different pins.

So, would it be possible to get a charger that has a USB end on it and use it to deliver both voltages, or is that not going to happen and leave me being forced to use two sources? Alternatively can the board itself supply enough power for a DFT11 temp/humidity sensor, a PIR sensor, a Maxin temperature sensor and the Wiznet ethernet shield with SD card socket on it without cooking? Will I still have enough spare juice to power an LCD as well (16x2 or a 128x64 if I can find a decent one), or is this a something that I will have to forgoe?

Any advice welcome... I'm new to all this and the last lot of practical electronics I did was about 20 years ago at school and resulted in a low grade for the exam.
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