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Recomendation for a newbie on electronics


#1

Hi,

To start, I’m a programmer and IT manager for over 14 years, know several programming language including C# and .Net, that is the main reason i choose fez panda II for my entrance to the electronic work and to used in a little proyect.From the old days of coaxial network I know how to handle a solder but that is all i know of electronic :slight_smile:

well, to the point, I’m just a couple of days to start buying the parts, including the panda II, that i need…but i’m loss on several points. let see…in general the project will be to control an aquarium, will have two parts, one main box where the ph controller, relays etc etc… and most of the software logic will be. the other part is a remote box, where the fez touch will be in so the user can be at any place on the house and control everything, it will only have the software logic to accept the info from the main box via wireless and display it on the screen, also accepting user commands and sending it to the main box.

For what i read for the comunication of the two boxes/units i will need two xbee for wireless, but my first question comes from power not comunication.

How can i power the remote unit? with a battery? what kind and how much batteries do i need to power the remote unit with fez touch? how can i recharge the battery when i plug the remote to the wall?

thanks…


#2

There are two options on the batteries from my point:
*Normal AA / 9v batteries
*Lipo battery

AA Battery:
PRO:
*Cheap
*Can get it everywhere
*Easy to charge

CON:
*Endurance

LIPO Battery:
PRO:
*Endurance

CON:
*You need a charger + balancer
*More expensive
*Risk of fire (only with damaged lipo cells - not common)

To be honest, the lipo may seem to be not as good as AA batteries. But what I find fantastic is that they have a high endurance.

Of course, this can be achieved with AA too, but those endurance (eneloop for example) AA batteries also cost more.

From the other point of view: why would you want to control your aquarium from anywhere in your house?
*PH/KH/etc. can be read on the control box
*Feeding is probably done by hand, but can be automated with timer
*Light is controlled by timers

What would the wireless device do?


#3

For portable applications I use a rechargeable 9V battery, which I bought on Amazon with a charger.

I was also able to buy a small plastic box, a little bigger that the 9V battery, which included a power plug which was compatible with a FEZ and a switch. The box costs about $5.

The battery has a 1800 milliamp hour rating. The Panda II draws about 100 milliamps, without the touch. So, the basic Panda II would run for about 18 hours on a fully charged battery. You would have to subtract the power needed for the touch to get the exact duration.

**** Ooops. I think I got the battery on EBay from China. 1800 sounds much too high of a capacity. I think it might have been more like 200+ ma/hours.


#4

I’m a big fan of Lipo batteries, as they provide the most power “density” for their size. The trade off is cost, both in the battery itself, and the charging hardware.

There are reasonably priced inline chargers available that run off USB power. Alternatively, you can save on money/complexity and just run your remote via USB power, keeping it plugged in most of the time, and getting something like Adafruit’s MintyBoost http://www.adafruit.com/products/14 when you need battery power. The nice part about this latter option is the Minty will power any USB gadget, and is a easy, fun kit to make.

As you can see there are a dizzying amount of options. It generally boils down to balancing cost with design requirements.


#5

robert :

first the control box would be in the least visible place (to hide the cables and power/relay box) but i want the screen/touch be accesible at any time, to see status and change something.

the remote box will only house the panda, the touch, the xbee and the basic logic to recieve info from the control box and display it

I will check the 3 options (AA, lipo, mintyboost)…how much power do the touch need?


#6

Instead of XBee and twice the hardware why not just build in a web interface that you could control through wi-fi with your phone/computer?


#7

ianlee 74:

I’ve the web control on the plans but that is when i’m outside of the house.

I can have just one box with the screen touch and everything…but the project will have a power bar with relays to control pumps and other equipment so they need to be as close as possible to the equipment but not visible, so i want to separate the control box from the user input/info display aka remote box

I’m studing the power options…i’m looking for the power req of the touch…


#8

what is a balancer and why do i need one with a lipo?


#9

Lipos can have one or more cells. A one cell is ~3.7V, a two cell, ~7.4, etc. You do not need a balancer for one cell lipos. If you have a 2 cell or greater, they need to be “balanced” when charged, so the cells end up with the same power (voltage and current) in each cell. This allows them to discharge evenly, as well, and extends overall battery life to some extent.


#10

You can also get a charger+ boost converter in one from Sparkfun for about $20, I used it for my proof-of-concpet. Was pretty happy w 3+ hrs of life on a fairly power hungry device. Using their second smallest single cell lipo


#11

Also a great Li-Ion & LiPoly tutorial :slight_smile: :
http://www.ladyada.net/learn/lipoly/

LiPo batteries can be dangerous if mishandled, so better know a little bit about it :-[


#12

Skewworks :

you mean this one ?

I’m looking at it right now.

nicolas3 :

thanks for the tutorial


#13

That’s the one. I believe this is the battery I used http://www.sparkfun.com/products/8483


#14

thanks Skewworks, i’m going for lipo using that charger and that bat…


#15

Skewworks :

with that charger how do i connect it to the panda II to suply it with power and how do i connect it so it can use the power plug from the panda to charge and not the mini usb.

Also how can i check how much charge the battery have?, with software? hardware?


#16

@ skewworks please chime in…

You’ll need to get a 2.1mm barrel jack http://www.sparkfun.com/products/10287 and 2 pin JST http://www.sparkfun.com/products/8670

For an onboard voltage check, you can build a simple voltage divider (2 resistors - google it for specifics) and measure it with the panda in code, or you can get something like this: http://www.adafruit.com/products/460

A word of caution: a single cell lipo, stepped up to 5V may not adequately power the Touch. I have not used that specific stepup/charger combo from SF, but have attempted to power the Touch by stepping up a lipo to 5V with a similar combination of components. Plugged into USB, the Touch would run and the lipo would charge. There was not enough power to run the Touch on battery alone. The Panda did have enough power, however, and I could collect data from a sensor or two. I just could not display it while on battery. It’s always a good idea to leave “a little extra” power (both voltage and current) for headroom when doing the math.


#17

Sorry, long day at work.

You can charge over USB (there’s a connector on the board)
There’s PTH connections so you can solder jumpers from the LiPo board to your main board.
A simple voltage divider will help you know how much power is available.

In reply to Architect’s warning it will power it more than fine. My board was a Cobra w/ 4.3 touch screen, 6 buttons, Joystick, MP3 decoder, speaker and connected USB device. All fine. :slight_smile:


#18

Just spotted this http://www.liquidware.com/shop/show/MBP/Lithium+Backpack would this be compatible?


#19

Sure… it just provides power, so you could use it to run anything that likes 5V or 3.3V.


#20

HughB :

thanks, that backpack is great, more expensive but i will give it a look.