simple power shield for wifi robot

is it possible to use 2 nokia BP-4L (3.7v 1500mAh) battery's to power a arduino. i want to put 2 of them in series and desolder the headers of a protoshield and my arduino and switch them so the batterypack is under the arduino.

question 1 how to charge them (use internal 3.3v or use a variable voltage regulator) ansered: BP-4L are lipo's so need a max1555 or equal.

question 2 is it possible to indicate the power to the script (not just a led that turns on or off) but realtime in % and a blinkM that changes for visual indication

its for my wifibot that is using a 12v battery (WRT54G, arduino+ethernetshield and 2 fans) and a 7.2v battery pack for driving since my robot is NOT YET capable of docking its self but i'm getting there

idea came to me when I found my dead nokia E90 again

Everyone warns against trying to charge LiPo batteries unless you are using a special circuit to keep from overheating/overcharging.

Well mainly to avoid them catching on fire or blowing up. Thankfully soon there may be a better battery without quite the same risks:


MAX1555 !! oooh thats small :P not sure if gonna take that route but its a good option! thanks man.

the extra battery is just because i want the arduino to be the last device to die on me. and just to have a good power source for it not a shared one.

does anny body know a place to order self-etc pcb's because i'm gonna try that to. already have a layout already made with fritzing.

with a h-bridge chip,rst button (offcourse) ,extra button , RS233 , 2x 7805's, servo-header and nunchuck/blinkM/i2c header

the rs233 is for talking to the Router if i may ever change my mind about the communication. currently using the ethernetshield.

just to let you know you dont need the rs232 chip to comunicate with the wrt54g just hook it strait to the arduino. the wrt54g uses 3.3v rx and tx lines so no need to add something thats not needed. and yes it has been tested this is how i have mine setup

Richard Crowley yes that is a great idea I didn't think of that but how do I monitor the battery ?

ABC-King Mmm really... gonna try that out in a few moments :P now that i think about it its straight forward I got the idea from the wifi bot from JB he uses a Serial arduino...

did'nt know that is was 3.3v serial on the arduino Well i'll have some space :P back on my pcb

what is the best way to charge a 12v 1,6Ah battery? i use a 13,2v 2A adaptor from my WRT54G

not quite sure about charging the bat cause you did not say what type it is . NI-MH - NI-CD , LI-PO , LI-ION and without that no one can answer that but why do you need 13V? the wrt54 will fuction just fine with as low as 7V if i remember it correctly. im currently using 1 7.2V 1200mah ni-cd and i get anywhere between 1 to 2 hours of run time on just the router(and the batt is about 4 years old). and if you drop the signal strength and cpu speed it will last a lil while longer and since its for a robot you dont have to worry about having it running at full power all you need it to do is send and recive a few bits here and there.

the battery is charging but i wanted to know if it can be faster and maybe a way to see if its full. i have to bring out my fluke everytime...

and if can charge more them one from one poers source say a PC-PSU or the 12v 2A wall adaptor i'm using now

its a sealed 12v lead acid battery I have about 20 of them (small ones LBH=10cm/4cm/5cm). and 6 big one of 7Ah but they are to big and heasvy for the robot.

I'm really gonna try the voltage divider and then save it's output to the eeprom when it lower then the last output. then see whats the lowest that it can run on and script from there.

fisrt time i'm using the eeprom :P could be fun :P

Wish i had payed more attention at my electronics class :P did get my diploma doh :)

I just found a part shop in my city (den haag) and gonna pay them a visit tomorrow :P see what I can get there. maybe some advise for selecting a chip for the charger. I hope they have self-etch pcb's (or what ever they call ém). would love to make a custum power shield :P

I always used online shops but the suck :P I really hate waiting ^^

// ----------------------------------------

this would be ok ? or do i have to use bigger resistors

  //          1k     1k     1k
  // 12v ---\/\/\/--\/\/\/--\/\/\/---0v
  //                     |
  // 12/3 = 4 = max         |-> analog 0
   float 12v_line = analogRead(0)*3; //
  if (12v_line >= 10) {
    Serial.println("Bat. LOW");
  } else if (12v_line >= 7) {
    Serial.println("Bat. VERY LOW");
    Serial.println("Change BAT");
    blink_led(100); // headlights blink rapidly

code above doesn’t work :stuck_out_tongue:
this is better :smiley:

  //          1.5k     1.5k     1.5k
  // 12v ---\/\/\/--\/\/\/--\/\/\/---0v
  //                      |
  // 12/3 = 4                 |-> analog 1
  // 5v = 1024
  // 4v = 819
  float voltage_line = analogRead(1);
  voltage_line = map(voltage_line, 0, 819, 0, 12);
  Serial.println("v");               // output voltage level
  if (voltage_line <= 8) {             // if 12v line = under 8 volts give  error
    Serial.println("low batery!");
    blink_led();                     // headlights blink rapidly
    low_power = true;
  } else {
    low_power = false;        

Did you get your voltage monitor working?

and you said you found a part shop in your city, there are actually 2: Radio Twente and Stuut en Bruin Radio Twente has a nice shop where all parts are laid out, but imho is not that helpfull, Stuut en Bruin has more modern parts like microcontrollers (yes thats modern when compared to Radio Twente's product range) and are really helpfull. But Radio Twente has alot more old-school / vintage parts.

They are like any other brick and mortar store alot more expensive than online stores

I exualy did get it to work and I'm very happy with it because now I know when to stop driving. and the charger does still work but I would love to see the progress.

and i will check out the "radio twente" store someday i haven't had time to go to "stuut en bruin" because I'm helping a friend moving out.