I used it back in the Pyxis One days. It’s ok, not spectacular and unless they’ve fixed it the status pin is worthless.
what happen to the status pin? that is the main reason to consider it against the Power Cell - LiPo Charger/Booster board
It was just a straight out line when I got it (granted that was a couple years ago), no voltage divider so it made it absolutely worthless for telling the “status” of the pack. Liquidware’s a good company though so they’ve likely fixed it, though there focus is more on Android these days.
for the Power Cell - LiPo Charger/Booster with the 2000mah lipo, how do i build a divider to meassure battery, i mean what vaule do i need the resistors to be?
It doesn’t matter as long as they are different. The formula is
Vout = Z2 / (Z1 + Z2) * Vin
where
Z1 = resistor #1
Z2 = resistor #2
Vin = input voltage
Vout = output voltage
The resistors for a divider can be the same, which splits the output exactly in half. Lipos shouldn’t go below 2.1v (I think, so check that) or they get damaged. Also they don’t go over 4.2, or shouldn’t, so using a divider with two of the same resistors gets you a measurement range of ~1.1-2.1v, which the analog pins on the panda can handle just fine. To measure higher voltages, just adjust the resistor values to bring Vout down to 0-3.3v - the range of the analog pins.
thanks
also found this
http://people.clarkson.edu/~jsvoboda/eta/designLab/VoltageDividerDesign.html…
nice calculator
i’m new to this but i think lipo that have under/over voltage protection will be cut off, right?.. from the datasheet for the lip 2000mah :
Nominal Capacity 2000 mAh 0.2C5A discharge
Nominal Voltage 3.7V Average Voltage at 0.2C5A discharge
Charge Current Standard0.2 C5AMax1C5A Working temperature040
Charge cut-off Voltage 4.20±0.03V
Standard Discharge Current 0.2C5A Working temperature-2060
Max Discharge Current 2.0C5A Working temperature060
Discharge cut-off Voltage 2.75 V
Cell Voltage 3.7-3.9 V When leave factory
Impedance 300 m AC 1KHz after 50% charge
Weight Approx: 37g
Storage
temperature
1month -2045
3month 030
6month 20±5
Storage humidity 65±20% RH
Best 20±5 for long-time storage
That’s the way I understand it. However, depending on your application you may not want to depend on that. It wouldn’t be good to have a copter just cut off in mid flight 
ianlee74 :
i'm with you...but i'm not doing a copter :)
let me see if i got it…
I make a voltage divider with 2 1k resistor and connect that to a pin on the board, from where i will read a value from (2.75/2) 1.375V to (4.2/2) 2.1V
now, for actual meassuring/control i need to take action like shutdown the remote box before the battery full drain, at 1.375v. At full charge (2.1) i dont need to do anything because the battery have protection.
what I missed?
what should be the code to read the value from the divider?
another general electronics question :
I’m buying the most used tools, aside from the panda, solder and multimeter…what electronics components will i need to buy that are comonly used in a proyect? an example could be resistors, what more?
My starter toolbox would have these:
- Breadboard, power supply, jumpers etc. - so you can build stuff
- 1/4W Resistors, 220R, 470R, 1K and 10K - so you can control voltage and current - learn Ohms Law before anything else
- LEDs - so you can see stuff happening in front of your eyes
- Tactile Switches or DIP switches - so you can control things with your hands
- ULN2803 Darlington Driver array (8 transistors in a chip) - because you will want to turn a motor at some point
- 12V relays - use with ULN2803 - because relays are simple to control and has endless possibilities
- Fez Panda II - because life would be dull without silicon brains
- Multimeter - because it will probably not work first time
I’ve been watching this thread because I have the same need for my current project and spent a little time researching solutions to this problem. I was having a problem understanding how a voltage divider helps solve this problem. What I’ve found in other discussions is that especially for LiPo batteries measuring voltage isn’t real useful because the discharge curve is very flat until the very end of the discharge (not linear). So, you might get 3.3V until the last minute or so of life and then it will drop off quickly. It seems that the best solution others are using is to basically build a static table of voltages or use run time to estimate the battery life remaining. To do this you discharge and measure through the life of the discharge in the lab to determine what your voltages over time and max runtime will be for your battery. Unfortunately, this also means that you have to re-do these measurements if you change battery sizes. If any of our electronics geniouses on the forum could ring in, I’m interested in hearing your thoughts.
Regarding the parts to start with… Unless you have an unlimited budget, I suggest you use my method. First, go to eBay and spend a few bucks grabbing some assortment bags of resistors & capacitors. Next, pick a project. Order 10x or more of all the basic [cheaper] parts required for that project. Build it. Do the same for every project after that. Eventually, you’ll have a fairly nice stock and you won’t spend a lot of money at once doing it.
I’ve heard similar advise from someone before and I am using it too. Different multiplier though. ;D
Yea, actually my multiplier is far from static and depends on the cost of the item, the ability to get it in bulk, and my available funds at the moment. Usually, my process is to check eBay for large bulk packs at low cost. If nothing there then I’ll resort to adafruit.com or sparkfun.com (in that order). Another place to get bulk and spend lots of $$$ is
Goldmine has prices like second hand but is first hand.
Like Pollin in Germany.
I like to have a roll of Gaussian Surface in my toolbox.
A Balck Hole would be handy too.
Black holes tend to be too heavy, and not practical for portable devices. Side effects on users are also an issue.
I’ll just use for all the junk in the shop.