Constant current load board for plotting discharge curves

I hacked together a constant current load board for the LiPo batteries so I can record and plot discharge curves. The hand-drawn schematic is shown below. I used parts that I had lying around, including an LMC660AIN quad op-amp, an NDP706BEL logic-level input N-channel MOSFET, and a 10-turn 5-kOhm potentiometer. I ran to the local Radio Shack to pick up the 1-Ohm, 10-Watt power resistor. I was pleasantly surprised they actually had that sort of thing anymore! Read On →

Solar cells arrived (finally!!!)

I had placed an order for a few different solar cells from Futurlec back in February. I knew they could take a while, coming from Malaysia, so I didn’t really pay attention until about the end of March, when I realized I hadn’t even gotten any notification that they had shipped. When I emailed Futurlec to inquire about the order, the response was that one of the units was out of stock and they didn’t expect to receive them in the immediate future. Read On →

Rev. B Solar Charger Board Received and Assembled

Rev. B Solar Charger Board I received the Rev. B boards back from OSHPark a couple of weeks ago. I assembled one of them, this time using a stencil and squeegee just for the QFN IC and then a syringe to manually apply solder paste to the rest of the SMT components. I thought that might be the way to do it in order to get good results without needing a new stencil for the whole board. Read On →

Rev. B Solar Boards Ordered!

Solar LiPo Charger and 3.3V Nano-Power Buck Regulator Board, Rev. B Woohoo! I finally got my second set of boards ordered from OSHPark for the Solar LiPo Charger and 3.3V Nano-Power Buck Regulator design. I also ordered a few different capacities of 3.7V LiPo batteries from AdaFruit, as well as a few different solar cells from Futurlec. I can’t wait to try out my modifications. Here’s a quick list of the changes I made: Changed the footprints of the JST 2-pin connectors to allow the pins to fit in the holes Consolidated a couple of JST connectors to a simple 0.1″ header for the output connector Added a level translator to put the VBAT_OK signal on the VOUT rail (0-3.3V) instead of VBAT (0-4.2V) Added a resistor divider to output VBAT/2 (0-2.1V) on the output connector to allow easier monitoring of VBAT voltage by a microcontroller Added a large electrolytic capacitor on VOUT So hopefully in a few weeks I’ll be able to finish my characterization if all goes well.

bq25570 Board Debug

In my spare time (which is a rare commodity), I’m in the process of debugging the bq25570-based Solar Li-Poly Charger and 3.3V Buck board. You can see my messy workbench in the photo below. I’m working through the issues with the board and the limitations of the circuit. My current setup uses eight “garden light” solar cells for the power source and a 1S (3.7V nominal) Li-Poly battery rated at 145mAh for energy storage. Read On →

First PCBs Arrived!

Solar LiPo Charger and 3.3V Buck Regulator PCBs The proto PCBs arrived from OSHPark for my Solar LiPo Charger and 3.3V Buck Regulator board! This board is based on the newly released bq25570 IC from Texas Instruments. This powerful little chip combines an ultra low power energy harvester with a boost charger and a nano-powered buck converter. What is all of that good for? Well, powering an MSP430 microcontroller from a solar cell with a small Lithium Polymer battery for backup, of course! Read On →

Launched Mile High Robotics LLC

Well, I finally did it. I started a company and website to begin publishing a blog and producing a few things for the electronics and robotics hobbyist community. I’m planning to start small and see how it goes. I came up with a company name that I thought made sense, tried to make sure it wasn’t already taken, registered the domain name, and then submitted the relevant online forms to launch an LLC in the state of Colorado. Read On →

Foam and Fiberglass Composite Robot Shell

Click here to go to my robot shell project page. This is my first attempt at using fiberglass and foam to make a strong but lightweight shell for my new robot. I’m basing it on Robert Q. Riley’s excellent article One-Off Construction Using Fiberglass Over Urethane Foam.

Futurlec ATMEGA Board Edits

I bought an ATMEGA board from Futurlec to use as a controller in my new robot I’m building, since it has the wonderful Atmel ATmega128 microcontroller and several 10-pin expansion connectors and RS-232 transceivers already on the board. I was frustrated when I couldn’t get my brand new ATAVRISP mk II USB programmer to talk to the board (through a 6-pin to 10-pin adapter I made). I discovered that there was bus contention on the UART0 Receive Data signal because of the way the board is designed. Read On →

Gimp Basics

Click anywhere on this paragraph to go to the new tutorial on using the free Gimp program to do things like resizing images, adding drop-shadows, and making transparent backgrounds!