Wednesday, February 20, 2013

Battery Charging - Part 6

My float charger that is based on ideas I stole from the Harbor City 42292 device has gone through another iteration.  I decided to actually have a circuit board made that would hold the components and allow me to mount the board properly.  Using Eagle, I drew up a board which included the charger parts and everything necessary to support the XBee.  It was fun and came back looking like this:

It was so cool getting my first printed circuit board design back in the mail, so I rushed right in and assembled it.  Naturally, there were a lot of problems.  I hooked the voltage divider for the analog measurement to the wrong pin on the XBee and had trouble telling it was transmitting because I didn't include  troubleshooting lights to look at.  I got Eagle back up and changed the design, and ordered another board.

On this one I also increased the size of some of the traces and moved the voltage regulators around so I could use the heatsink I kept from the original charger.  So, I populated the board and hooked it to the lid of the box.  The entire device looks like this:

I happened to catch the leds on in the picture, but they are disconnected in a running device because they draw unnecessary power when it is actually in use.  It works real nice, and keeps the battery voltage at a constant 13.4 volts.  I've had several hand wired ones in place for months now and they are doing the job.

I'm still not done though.  I discovered a way to sense current being put out by the device.  I can put a hall sensor over a trace on the board that carries current and it will change output relative to the current flowing through the trace.  I doubt that I can tell the exact amount of current passing through the trace, but I can certainly tell if it is actually charging the battery.  This idea will take some development though and I don't know what components will be necessary for the final result, so I'll just assemble the rest of them and put them to work. I hope to get back to the hall effect device idea in a couple of months and work out the details.  The previous post on these devices is here <link>

I learned a lot creating the board, and I think I can develop boards for other ideas I have.  Things like a timer that will catch the time broadcast on my XBee network to operate lights and other devices would be great. It gets to be a real pain tediously connecting wires on a protoboard, especially when you want several identical devices.  Having an XBee network and something like this means I can finally get rid of the X10 devices that are so unreliable.  It would be so cool to completely switch over to XBee throughout the house.


  1. That is so cool! Back in the day, (80's) it cost around $2000 for small boards like this. It was as cheap to do 1 as it was to do 20 because of set up charges. That was fine for my job, but far too expensive for my hobby.

    I take it you found somewhere reasonable to get boards done? I agree with you, doing this by hand is hard, especially with older eyes. I would love to get some PCBs for some of my ideas if it is affordable!

    I finally got my first XBee doings something useful. I have a ribbon of LEDs on tape attached to the bottom of my stairway banister. A Teensy controls the light level via PWM. Included are a motion detector and photo cell with an Xbee for communications.

    On the other end I have a Linux box and a Raspberry pi with XBees and code written in Perl. The Linux box is mostly for debugging my code.

    The lights are commanded to turn on or off based on time of day or because of motion detected.

    My next project, is a refrigerator temperature sensor. Every once in a while, someone bumps one of the controls and my vegetables freeze. Anyway, that is the excuse I am using to monitor it. I am still trying to decide the best way for notification in the event things are getting too cold, but it will most likely involve an XBee.


  2. I got the boards done at They're pretty reasonable (subjectively) for small orders, like one or two. I could have done it cheaper, but I didn't want to learn all about pcbs in order to get my feet wet.

    I love the idea of lights that sense when you're coming and turn on. Especially when they dim automatically as it gets darker so you don't go blind at night.

    I've been looking at my fridge for three years now. My objective is to sample the temperature (of course) and also track the compressor. I want to actually turn the compressor off during peak usage times when my electricity costs go way up, then kick it back on when the cost goes back to normal. You'll see that project on this site in a month or so because I finally figured out how to do most of it. The cool part is that an XBee can do the sensing and even control a relay to shut things down without a processor in the box. This could get to be fun.

    By the way, I had problems with stuff freezing up and it wasn't a misadjustment. Seems the darn air flow was bad and the bottom got super cold and the top just normal. I had to fix a fan switch to fix it. This most likely isn't your problem, but keep it in mind.