Using 3.3v converter #1066 with Due and Logger Shield #1141

Adafruit Ethernet, Motor, Proto, Wave, Datalogger, GPS Shields - etc!

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
leem
 
Posts: 9
Joined: Sat Dec 21, 2013 12:31 pm

Using 3.3v converter #1066 with Due and Logger Shield #1141

Post by leem »

The question is: How to power my mapper with a 3.3 volt downconverter and a little bit of the 10.2 volt battery pack. The mapper uses an Arduino Due and an Adafruit Logger and both parts seem to need a little bit of 5 volt power.

I am building an atmospheric carbon dioxide mapper. The main unit is an Arduino Due because it has many serial ports. I am reading a CO2 meter with one serial port and then reading an Ultimate GPS with another serial port, and then reading a BP180 barometer by the first SDA/SCL port and then reading the RealTime clock on the Logger using the Due's second SDA/SCL port. Then a long line of data is writtten out to the Adafruit Logger Shield using the SPI serial peripheral interface.

After the first one day test I was getting only 7 hours out of four rechargable AA size cells.

I did not measure the current flow in the battery leads and I suppose I should do that now.

It has been enough of a hassle getting the DUE to dependably parse each item of data I really don't want to risk the dependability of the data making the GPS device sleep. This mapper needs to run and run whether I am carrying it by hand in a forest or greenhouse, riding the bus, driving in a car, sailing to the Farralons or riding in a small plane or helicopter.

To get longer run time I changed to an eight cell battery pack and the Adafruit efficient switching downconverter device.

I doubled the battery pack to eight rechargable AA cells that put out about 10.8 volts and have a rating of something over 1200 maH. Then I put the Adafruit #1066 mini DC/DC 3.3 volt downconverter on the Logger shield prototyping area.

From the battery pack I have about 10.8 volts DC. So far, the 3.3 volt downconverter is powering the Ultimate GPS and the BP180 barometer just fine. The Arduino Due and the Logger need a little bit of 5 volt power and 3.3 volts. I have not figured out where to supply the 5 volts. I want to get the most work out of the downconverter because it is a switching power supply.

Regarding the the Arduino Logger, I see the DS1307 clock needs 5 volts and thanks to an earlier Forum post, I see two 2.2k pull up resistors attached between the 5 volts and the SDA and SDC lines. I am somewhat puzzled about how the Arduino Due power works. Vin appears to be where you apply big Wall Wart DC voltages. The Due I think has two on board pass type voltage regulators. Why doesn't a trickle of current applied to Vin give the trickle of +5 needed by the Logger?

I tried this power plan. I jumpered +5, +3.3 and GND between the Due and the Logger. Further, the two cards are connected by the five SPI wires and the SDA/SCL wires. The whole setup works when connected and powered by the micro USB cable. Then I tried a 1500 ohm resistor and the 10.2 volt battery voltage to supply current to the Arduino DUE Vin terminal. The Logger did not light up as when powered by USB. I tried a 680 ohm resistor. The Logger had dim LEDs and it wrote the same line of data several times. I felt sorry for it. I stopped that test right away. So the miserly trickle of current into Vin does not make the Logger happy.

Sorry to trouble you with this. I can switch breakout boards if necessary but I do need the battery backed RTC and I do need the SD Card writing capability. Cordially yours, Lee

User avatar
adafruit_support_mike
 
Posts: 67454
Joined: Thu Feb 11, 2010 2:51 pm

Re: Using 3.3v converter #1066 with Due and Logger Shield #1

Post by adafruit_support_mike »

You'll get better results using one of these: https://www.adafruit.com/products/1566

It's a 10,000mAh LiPo power brick with 5v output. Even if it isn't as efficent as a buck converter, it stores about three times as much energy as the power supply you're using now.

It would be very difficult to geet a Due to work from an external 3.3v supply. The ATmega16u2 chip that handles USB communication needs 5v, and there are some signal connections between that and the microprocessor. Broadly speaking, the Due is a 5v board that provides support for a 3.3v chip. If you try to bypass the 5v parts of the board, you end up fighting with them.

Locked
Please be positive and constructive with your questions and comments.

Return to “Arduino Shields from Adafruit”