My meped just resets

[PacMan]

I just finished my meped after a few hours of great fun. Put some new alkaline batteries in to start testing. Unfortunatly it will not move, Instead the nano resets as soon as I try to move it. I can hold it in the air and it will do a few steps but will ultimatly reset.

Any pointers anyone?

/Pontus

[spierce]

Hi PacMan,

What you're seeing is a condition know as a "brown out". The Arduino is starting up and it begins to move the servos to their center (90 degree) position and this causes a spike in power usage. This can cause the battery voltage to dip just below the minimum threshold needed by the Arduino to function properly so it resets itself. This can typically be fixed by installing a new or fully charged set of batteries.

The odd thing is, as you mentioned, you put a fresh set of Alkaline batteries in the mePed and you're still seeing this issue. Alkaline batteries put out 1.5v each which would give you 6v total to the Arduino and servos. We have two 1N5817 Schottky Diodes on the board that drop the 6v down by about .9v, giving us 5.1v to the Arduino. The servos are not regulated by the diodes so they get the full 6v. When using rechargeable batteries, the voltage of each cell is typically 1.2v, giving us 4.8v before the diodes, dropping down to 3.9v after the diodes, going into the Arduino. Again, the servos get full battery pack voltage of 4.8v.

I personally have been using Duracell NiMH rechargeable batteries that operate at 1.2v and contain 2500 mAh capacity. These typically run the mePed for about 20-30 minutes on a charge when showing the mePed at Maker Faires. There are a lot of Alkaline batteries out there that only have a capacity of about 1200 mAh and I have a hunch that since their capacity is so low, it could cause the Arduino to brown out much sooner.

I know this might be inconvenient but one thing you can try, if you're comfortable with soldering, is to remove one of the diodes from the circuit board and solder in a piece of wire in its place. This will give your Arduino .45v more than what it's currently receiving, which might prevent the brown outs from happening.

I apologize for the troubles you are having. Please let me know if you are able to remove one of the diodes and solder in a jumper wire and if this solved the issue.

Thanks,
Scott Pierce

[spierce]

Following up on my previous post about removing one of the diodes and replacing it with a jumper wire, I was able to recreate the brown out situation using a fresh set of alkaline batteries. After that, I set up one mePed with stock hardware where the PCB has both diodes on it. I set up a second mePed where I removed one diode and replaced it with a jumper wire. Please see the attached image for reference.

After setting up both mePeds, I put a new set of alkaline batteries in the stock (2 diodes) mePed and it ran fine for about 15 seconds before it started to repeatedly reset due to a brown out situation. I turned off the stock mePed, removed the alkaline batteries from it and placed them in the modified (1 diode & jumper wire) mePed and turned it on. Using the same batteries, the modified mePed had no issues with brown outs even after multiple minutes of walking around.

Unfortunately this issues didn't arise in our testing phase because we had always used high capacity NiMH rechargeable batteries which can supply more current and thus experience less of a voltage drop when in high current usage. I would suggest using batteries that have 2500 mAh capacity or higher. If you would still like to use alkaline batteries and are comfortable de-soldering the diode and replacing it with a jumper wire, that is another viable option.

[Grasshogger]

Scott,

Given that this is going to be an ongoing issue have you considered making board changes for your production runs, or front page notation on the need for higher capacity batteries? Most people are going to want to be able to use first grab, off the shelf, batteries otherwise.

Shawn

[spierce]

Hi Grasshogger,

We will definitely be making a revision to the PCB and we're currently reworking the existing boards in stock by removing one of the diodes and replacing it with a jumper wire to fix the brown out issue.

Thanks for the feedback!
Scott

[markroedel]

I don't trust myself to modify the board on my own...is it safe to assume at this point that a replacement circuit board ordered from the online shop would have this "fix" already applied?

[spierce]

Hi Markrodedel,

Yes, all boards purchased after after October of 2016 have the updated, single diode layout. Please contact us directly at sales@spierce.com and we'll be happy to assist you with your PCB and get you up and running!

Thanks,

Scott Pierce
SpierceTech