Shop OBEX P1 Docs P2 Docs Learn Events
7.4V LiPo power source for BS2? — Parallax Forums

7.4V LiPo power source for BS2?

wperkowperko Posts: 66
edited 2013-11-16 07:32 in BASIC Stamp
Hi,

What is the best way to connect a 7.4V LiPo battery to a BS2 chip?


Is it safe to directly connect to the Vin pin 24 on the BS2 chip?

OR

Do I have to regulate it with a seperate 5V regulator like on the BOE and HomeWork boards?


If I'm using a 7.4V LiPo and a 5V regulator do I connect the output of the regulator to the Vdd pin 21 AND the 7.4V to the Vin pin 24?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2013-11-09 08:12
    Sure, connect the 7.4V LiPo battery between Vin and Vss. The BS2 has a built-in 5V regulator there and the output of that regulator is connected to Vdd so you can use a small amount of current from there for sensors or other 5V circuitry. Note that the built-in regulator can only provide about 40mA. If you need more than that, you will need an external 5V regulator.

    If you're using a 7.4V LiPo battery and an external 5V regulator, you can either connect the output of the regulator to Vdd or you can connect the LiPo battery to Vin. By using the built-in regulator, you get a little more isolation between the Stamp's circuitry and the circuitry powered by the external 5V regulator ... useful if you're powering servo motors or other noisy circuitry off the external 5V regulated supply.
  • wperkowperko Posts: 66
    edited 2013-11-15 15:02
    Hi,

    thanks ... looking this up online I found all sorts of B.S. about batteries killing BS2 chips ... but it didn't make a lot of sense. This makes my BallBot1 robot and FloppyBots FaceBoard cheaper for end users.

    http://www.brainless.org/Robots.html
  • Mike GreenMike Green Posts: 23,101
    edited 2013-11-15 15:34
    The BS2 module commonly is run off a 9V battery ... not the best choice for battery capacity, but it works. The main issue is that excess voltage has to be dissipated as heat and the voltage regulator on the module has a minimal heatsink. As long as you're just running the BS2 itself without a lot of LEDs or other loads on it and its I/O pins, it works fine at 9V. 7.4V from a LiPo battery is even better since there's less heat to be dissipated. The Board of Education runs the BS2 module off Vin and everything else off the separate 5V regulator ... works great with a 9V battery (other than battery life) and it'll work fine using your 7.4V LiPo battery. The standard AC "wall wart" that Parallax supplies produces 7-7.5V ... roughly the same as your LiPo battery.
  • wperkowperko Posts: 66
    edited 2013-11-16 06:26
    Hi,

    So, is running the BS2 from the 5V regulator on Vdd pin a better solution?
  • Mike GreenMike Green Posts: 23,101
    edited 2013-11-16 07:32
    "better solution" ... maybe ... it depends.

    It depends on what you have connected to the Stamp's I/O pins and how much current is drawn. The regulator is limited to supply about 50mA at most with about 10mA used internally in the Stamp circuitry. The regulator may be limited further by operating temperature if too much power has to be dissipated. Any I/O pin loads to ground (where the I/O pin supplies a high signal) contribute to the current drawn by the Stamp. All you need are a couple of LEDs to exceed the 40mA limit. There are also limits on I/O pin current individually, in groups of 8 (0-7 and 8-15), and total for all I/O pins.

    If you're running the BS2 off 7V or higher, you have to keep in mind the current drawn and the heat issue particularly. The higher the voltage (and I/O pin current), the more likely you'll need to run the BS2 from an external regulator supplying 5V.
Sign In or Register to comment.