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1  Topics / Device Hacking / Re: Power problems connecting external device to Arduino UNO R3 on: April 09, 2013, 03:03:40 pm
And the Bluetooth Module? Can I have multiple wires from the 5V pin?  I don't think the 3.3 V pin is enough to power the Bluetooth module.

thanks,
andrew
2  Topics / Device Hacking / Re: Power problems connecting external device to Arduino UNO R3 on: April 09, 2013, 12:01:39 am
Generally you only connect the Ground between two systems with different voltage requirements.

John, actually I'm ok using two power supplies. Are you saying that connecting the ground and the vin from the 6V device to the UNO while powering the UNO with an additional 9V somehow prevents an over-voltage flow to the device?

3  Topics / Device Hacking / Re: Power problems connecting external device to Arduino UNO R3 on: April 08, 2013, 11:49:46 pm
Hello John,

Thanks for your response. I'm already using the +5V pin to power a Bluetooth module. But your 6V regulator idea makes a lot of sense to me. I'm new to electronics and didn't even know there was such a thing. Is there a specific component that comes to mind that you could recommend? I see an Adjustable voltage regulator at Sparkfun but nothing specifically for 6V.

Thanks again,
andrew
4  Topics / Device Hacking / Power problems connecting external device to Arduino UNO R3 on: April 07, 2013, 10:20:31 pm
Hello,

I hacked an off-the-shelf blood pressure monitor device that runs on 6V (4 AAA batteries) and connected it to an Arduino UNO R3 to have a program control the device. It is working but I'm having power problems. I have the positive and negative lines from the device connected to the UNO's Vin and GND. I need an Arduino program to ground another wire from the device to control it. However, the 6V from the device is not enough to power the UNO in a stable way, so I started connecting a 9V battery to the UNO's power jack or USB. Doing this works, but I noticed that the 9v power supply is flowing back to the the device from the Arduino. I don't want to fry the external device, but the UNO seems to need more than the 6V the device supplies. If I don't connect the UNO Vin and GND to the device the UNO/device interaction doesn't work. Is there an obvious way to connect the two components with two power supplies so that one won't burn out the other?

Thanks,
andrew
5  Using Arduino / LEDs and Multiplexing / Arduino ADK Port Register issue on: January 31, 2013, 06:09:59 pm
Hello,
I have an Arduino ADK board. I'm trying to use a built-in variable to monitor the digital input pins. For example, on my Arduino UNO
PORTD maps to Arduino digital pins 0 to 7
PIND - The Port D Input Pins Register - read only

With the UNO I can use the PIND variable successfully to monitor activity on the pins 0-7. However, this is not working with the ADK board. Although the "PIND" variable is defined I don't know what it maps to and I cannot find the info. For the UNO, there is this web page:
http://www.arduino.cc/en/Reference/PortManipulation

However, the page doesn't include the ADK's ATmega2560. How can I find the correct variable to use (if there even is one)?
Thanks,
andrew
6  Using Arduino / LEDs and Multiplexing / Re: How to use PORTD,PORTB in Arduino ADK Mega on: January 30, 2013, 04:28:48 pm
Hello John,

Have you found a solution? I have a similar situation: For an Arduino UNO project I'm using the PIND variable. In the UNO PORTD maps to Arduino digital pins 0 to 7. PIND is a variable for the Port D Input Pins Register - read only. I need the same information for the Mega ADK board - what is the equivalent variable for the digital input pin register 0 - 7?

thanks,

andrew
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