9V vs USB power in a classroom setting at K2

I just got done with the 1st littleBits based “Makers” class at my kids Elementary. We will have 7 more weeks teaching ~20 kids from KG to 2nd grade.

We kept running into battery issues, hence this question. Even though we tried each battery out the night before, several gave out during the class and we ran out of replacements!

What power sources do other educators use:
9V or USB power?

For 9V, do you use:
• NIMH Rechargeables (8.4v 200mAh)
–> is 200maH good enough for an hour long class?
• Or Li—Ion (7.2V 600mAh)
–> Will 7.2V LiIons work? I can’t find anywhere online that discusses if 7.2V Li–ions work with LittleBits.

For USB, has anyone solved the issue I notice with the circuit not staying in place because it’s so light compared to the pull from the USB cable ?
Does having USB also limit kids ability to show off their work to their fellow classmates, and versatility of certain projects (e.g. wearables), and should this be a factor in sticking to batteries?

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Hi @baselsalam :slight_smile:

Can you tell us more about how your workshops are organized?

If given the opportunity to use any and all Bits, kids in this age group do like to randomly connect Bits in no particular order. This can mean motors are running constantly, which is a big drain on batteries. If that is happening, I suggest you limit the Bits available to each child or group until they demonstrate mastery of pink Bits. Explain how color order is important. If you hear a buzzer or a motor running continuously for no apparent reason, say “Show me how you control that green Bit with a pink input Bit.”

There are times, however, when free play and investigation is important. For these times, a USB Bit is a PERFECT solution. As far as a USB Bit being weighed down due to the weight of a cord, I simply use a little masking tape to anchor it to the table. When it comes time to test a more portable version, simply swap out the USB power for the p1 with a 9v battery.

I hope that helps. I’ll let someone more knowledgeable about batteries comment on the types you have listed. :smile:

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Thanks for your reply!!

I can tell you do have real world experience with kids this young!!
Yeah after the first 20 mins we realized the kids were wildly just snapping things together. The snap itself seems addictive to them lol.

So for the last half hour of our class we made them put everything back, gave them a focused task (light controlled by a switch), and then they were able to complete the task and actually answer questions about what function the switch is doing.

So for each of the next few classes we are planning to do the same, introduce just 1/2 new pink bits, and one new green bit, and ask a focused question (e.g. make a door bell, and choose the appropriate input bits so it’s not too loud, and it turns off after u let go off ur finger).

Securing the USB down: ahhh masking tape. I was wondering about that (strong enough etc). Since it works for you I’ll try that! I’ve also ordered some “flat” USB cables which should be easier to secure down and also eliminate the “twist” with regular circular USB cables that makes the circuit not stay flat.

In addition, as you’ve suggested, we will also keep some 9V around for the more mobile projects like cars/wearables etc, or when they come to the front of the class to show off their work :slight_smile:

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Hi @baselsalam
Another idea is to use battery packs for cellphones, like these : http://www.bestbuy.com/site/cell-phone-batteries/external-battery-packs/pcmcat326000050010.c?id=pcmcat326000050010
These can be charged and can afterwards be used with the USB power bit.
They have a bigger capacity then normal 9V batteries. I often use one of them with my projects.
Rechargeable 9V batteries don’t last that long compared to these packs.
Greetings

Oh nice. So these small 2000mAH battery packs seem light enough to use in a mobile project!
Plus at $4 a pop they’re the price of a rechargeable 9V!

I use littleBits in conjunction with other electronics and mechanical systems in college project and laboratory environments. My favorite power supply is a , micro USB connector with a 1 meter long cable to a wall wart capable of a 2 amp current draw. On the littleBits side, it’s the USB power bit, often with a wire bit that has been cut in half, and male breadboard pins soldered to the +5V and GND lines. A shoe keeps the power and wire bits firmly attached…

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I ran into an interesting issue with these battery packs: they turn off after a few seconds if not much load is drawn.

To figure out the min load required, I pulled out my DROK USB meter, and started measuring bits.
Seems like the min required is >60mA, which is satisfied by USB power(10mA) + Bargraph (40mA) + LED (10mA).

Then I proceeded to measure the power draw of all the different types of Bits I have :slight_smile:

Final output :

Since each RGB LED draws 30mA max (recorded in the table above), I’ll prob just put two RGBs together (shielded by black paper), and hand these out as needed w a battery pack to students when they need portability or their USB cable isn’t working (happened with 3 students last class)