Arduino Pro Mini + accelerometer + leds questions

Hello everyone, I am currently trying to put a project together , that uses:

  • an arduino pro mini 3V3
  • a 3 axis MMA7260 accelerometer
  • an NCP1400 5V step up board
  • Two 4094 shift registers
  • Two sets of 8 green leds connected to the siftregisters via 500ohm resistors
  • it all need to run on 4 AA 1,5 batteries max

This needs to be integrated into a juggling tool (diabolo), and have at LEAST 15 to 30 minutes of runtime.

Now the thing is , i have never worked on "portable" projects like this before, and i am somewhat worried about the power requirements: I have not yet recieved the arduino min, accelerometer, and step up board, but : - have experimented with a set of 8 leds connected to the shiftregister , on a standard arduino's 3V3 port that can normally only source 50 ma and i didn't run into any problems even with more leds -From the datasheet, it seems the accelerometer only needs 500uA -if i understand correctly the arduino pro mini uses around 25mA -The max current from the step up is 100mA

Am i missing anything or should it be ok ? One alternative approach i could use is to seperate the general power supply from the led power supply, using a sparre 3,3V step up, but in that case each step up would only have 2 AA batteries avalaible.

Any advice would really be welcome! Thanks in advance!

What’s the 5V step up for?

It looks to me that everything could likely run on just two AAs, @ 3V. Have tehe 3V go directly to Vin on the promini, and not Raw.

With 500 ohm resistors, the LEDs will only be seeing 6mA max, so 1500mAH batteries would last a while.
(kinda awkward editing this after the fact, am not seeing the prior posts as I mod this for some reason).

ok, so you’ve got:
25 mA ?an arduino pro mini 3V3
0.5mA ?a 3 axis MMA7260 accelerometer → Low Voltage Operation: 2.2 V - 3.6 V
not needed? ?an NCP1400 5V step up board
<1mA ?Two 4094 shift registers → these will work as low as 2V also I believe
<96mA ?Two sets of 8 green leds connected to the siftregisters via 500ohm resistors (3V/500R=6mA * 16 96mA max, and actually less as the R will see more like 1.5V and not 3V).

Total: <125mA, should be more than 10 hours on 2 AAs at 3V.

Hello crossroads !

Thanks for the quick reply! Actually you are completely right, the step up is quite useless , i had forgotten about the fact that most modern batteries are well above 1500 maH! Thanks ! Talk about forgetting the obvious :)

One thing i don't quite understand though, why connect the supply to vin instead of raw ? i thought raw was for the input of an unregulated power supply ?

Why go thro the regulator & waste power when you can drive VCC on the Promini (not Vin, different board uses that). Batteries are about the most stable thing you can get outside of a regulated DC supply. Put a scope on one - not gonna see any ripple on that outout!

Look at this schematic for my remote control - you can'get much simpler for powering it.

I don't have the max1811 plugged in yet, need to order some panel mount 2.1mm connectors. But the rest, 3.3VPromini/8MHz, works great on 3AAs or a 1000mAH 3.7V LI ION battery.

I have it programmed to wake via interrupt on a keypress , send out the one button pressed, and then go right back to sleep (powerdown mode).

So replace my keypad & antenna with your accelerometer & shift registers/LEDs and have at it!