Thursday, June 20, 2013

Power Bank

I love free samples. Texas Instruments, Maxim IC, Microchip, and most other semiconductor manufacturers will send you quite a few parts for free, almost no questions asked as long as you are a student or engineer.

I discovered a new device by TI, the bq24195, that is able to efficiently charge a single cell Lithium ion or polymer battery, and also acts as a boost controller to boost the voltage to 5 volts in order to provide power to cell phones or tablets. It has lots of interesting features for controlling and monitoring the battery, and an I2C interface for control by a microcontroller.

I placed a sample order for a few of these devices as well as some TPS2511 USB port power switches from Texas Instruments, and am now building my own power bank/backup battery. It will be able to charge from any dc source between 5 and 20 volts, at up to 4.5 amps for quick charge times. The battery is a 1s2p Lithium polymer pack rated at 10,000 mAH, which should recharge my phone at least a couple times.

Many commercial backup batteries are severely over-rated as far as battery capacity goes, and some unscrupulous manufacturers even use recycled batteries. Good quality devices exist but can be expensive, plus I like the challenge of building my own to my own specifications. Currently I have the housing for the device made, and the circuit designed and laid out. The housing is made of walnut, and will feature two USB output ports, one micro USB charge port, and one dc input for higher voltage charging. The output ports use TI's TPS2511 device to allow my power bank to recharge almost any device. The microcontroller will be able to measure current exiting or entering the battery and will integrate over time to calculate the remaining capacity of the battery. Estimated charge state will be displayed on some LEDs on the outside of the case.

 The case is made from a solid piece of mahogany That I cut a pocket into. The top and bottom will probably be made of copperclad so I can build the display circuit directly onto the underside of the panel, allowing the display to shine through the PCB substrate. I've done this before, and it produces a good effect.

Sunday, June 2, 2013

Embedded systems.

My embedded systems course this quarter required us to come up with a development project containing an embedded system and work on it over the ten week quarter with a final presentation and demonstration at the end.  My group decided to break up into sub-groups and design several projects. My contributions were to help design and build a parking distance sensor that uses an ultrasonic rangefinder to determine how far away your car is, and alert you with an LED display when you have parked close enough. We also built a small system that uses the same sensors to detect objects around the sides and back of a car and alert the driver with an LED display on the dashboard. I was able to use my PCB making tools to develop professional looking prototypes of both systems for demo to the professor next week. The parking sensor project has an actual prototype, while the obstacle detection system has a nice clean board to demonstrate the sensors and the LED display to the class, since bringing a car to class isn't exactly feasible.

Radio, Completed.

After several hours of polishing and a complete set of new capacitors, The radio looks and works as well as it did when it was new! After installing the new capacitors it fired right up, and the AM receiver was working great, but I discovered a pentode tube with a burned out filament in one of the FM IF amplifier stages. After its replacement, FM radio works beautifully too. I found a replacement knob on the antique radio forums, and gave the gold emblems and trim a fresh coat of paint, and it is now finished! Very happy with how it has turned out, and its new polypropylene film capacitors should allow it to keep working well for many more years.