As I have been using my new 3Pi, I have been wondering how much power is being consumed by the blue power LEDs. I have looked over the wiring schematic and there does not appear to be a way to turn them off. Is there any easy work around?
The blue LEDs are probably drawing a total of around 5 mA from your batteries, which is a fairly insignificant amount on a robot with motors that draw orders of magnitude more current than this. The only way to turn them off is to desolder the LEDs or their current-limiting resistors, or you could cut the traces that power them, but the LEDs should essentially have a negligible impact on your 3pi’s battery life, so I really think this kind of modification is not worth the effort.
Hi Ben -
Thanks for the reply. I was curious over the power draw of the unit under minimal operation. I was working with the 3Pi writing small programs that utilized the LCD, the on-board red and green LEDs and buttons A, B and C. After about a two hours the voltage of a new set of Duracell alkaline batteries had decreased from 6.1 V to just a bit over 5 V. I looked up the voltage-current characteristics of the AAA batteries, and a voltage drop of ~0.25 V per cell in two hours of service corresponds to a continuous current draw of approximately 0.1 Amps. This seems a little high for what I was doing, and I thought that the bright blue LEDs might be responsible if they had a higher current rating. Could some of the current drain be related to the step-up regulator?
Not a big deal (I have ordered a two sets of rechargeable batteries), just curious…
p.s. I am also putting together a site that provides access to all the simple “test” programs I have been writing. I mean for it to be a tutorial site for novice users. The link is here:
The combined idle current draw for the 3pi is indeed around 100 mA, of which the blue LED contribution is around 5%. I just measured the current draw of a 3pi running the intro screen of the demo program and got 81 mA when VBAT was 5 V (144 mA with the reflectance sensor emitters on) and 72 mA when VBAT was 6 V. The electronics are powered from a linear regulator fed by the boost regulator, which makes the current drawn from the batteries proportionally higher by:
9.25V / (battery voltage * regulator efficiency)
This is probably generally close to a factor of two, and it is acting on the combined current draw of the MCU, regulators, motor driver, and LCD.
Thank you for sharing your test programs; it looks like it could make a good resource for new 3pi users. Please keep us updated on your progress!
Hi Ben -
Thanks for the information. I guess the rechargeable batteries are definitely a necessity. Maybe I will think about adding a jack where I could use a 6 Vdc power supply when I am just testing programs.
I’ll keep you up to date on the progress of the tutorials.