Archive for the ‘Electronics’ Category

Roomba battery

Thursday, February 24th, 2011

Several years ago I got a good deal on a used Romba Discovery. A good cleaning and an AC adapter from the parts bin later it worked fine. The battery didn’t have much life in it after a few months of use so I bought another on eBay and all was well.

Fast forward a couple of years and the little robot had fallen into disuse but still sat patiently on its charger. Upon trying to start to use it again the battery gave out. After a charge it would give anywhere from 1 to 30 seconds of run time before flashing red and crying pitifully that it needed a charge. Some internet searching and forum reading led to a battery conditioning technique that is recommended by the manufacturer. I also took this opportunity to finally build a serial interface for the Roomba (more bits from the parts bin = $0 cost). Thanks to a few lines of Perl to parse the serial output and gnuplot I have pretty graphs of the battery charging cycle (that is currently 52 hours into the recommended 72 hours).

Click on the graphs to embiggen.

Here is voltage and current for the first 52 hours. You can see that the most interesting stuff happens in the first 17 hours.

 

Here is voltage/current and voltage/temperature for the first 17 hours. Something radical appears to happen around the 3 1/2 hour mark.

 

Hmmm, not sure what that means. Did the battery do something (possibly vent) due to heat? 40C isn’t all that warm but who knows.

After the 72 hours is up I will run the Roomba and see what kind of behavior I get.

 

Update

The battery did not respond to the reconditioning. One new battery from eBay later and the Roomba is back to normal.

CNC first cut

Wednesday, December 1st, 2010

I finally made some sawdust tonight.

http://www.youtube.com/watch?v=h4-6bVEZ7_U

It’s alive!

Monday, November 1st, 2010

My HobbyCNC Pro kit arrived the other day and several evenings later I had the steppers moving. My son (age 3) and I enjoyed watching the steppers move on the workbench as EMC thought it cut out the standard test image. I also made more progress on the CNC machine build. In spite of several layout errors I have the X and Y axis pretty much assembled. The X axis is mostly dialed in but there is a bit of slack in the end bearing. These bearings may end up getting replaced if I can not eliminate enough play. Sadly I broke a tap while fabricating my stepper coupler so I did not achieve CNC movement as hoped this weekend.


AVR DDS Function Generator

Thursday, October 21st, 2010

I ran across this link via Hack a Day for an AVR based function generator. My workbench has needed a function generator for a long time and this looks like it would fit the bill nicely. Now to find the time to actually build the ting…