USB Coin/Button Cell Battery Charger

I have designed many small footprint PIC projects (such as, pocket watches and wristwatches) but I cannot make them really portable. To make them portable, I need small power sources. Of course, Coin Cell battery would be the smallest DC source that I can buy. The problem is that a Lithium button cell provides 3 V. which is not enough to drive my projects. I thought about using DC-DC step-up converter to boost 3 V. to 5 V. However, it's a little bit complex to add DC-DC converter to the projects. Moreover, my projects consume a lot of power as they consist of many LEDs, a button battery will not last for a day. So, I stopped my think at that point.

Just recently, I have found a rechargeable coin cell battery at Sparkfun.com. It provides 3.7 V. at 200mAh. I don't know that my projects will work at 3.7 V. or not. But, I want to give it a try. For portability, I want to charge the battery from my computer's USB port. So, I designed a USB coin cell battery + charger breakout board. Like many simple battery charger, I use MAX 1555 as the controller of the charger.

The schematic:


The single sided PCB (40mm x 30mm):

The LED goes off when the battery is fully charged (but the charger is still charging).
Please note that the schematic/PCB are just the design and I haven't made it yet. The parts are ordered and I will update when I complete the hardware.

Multisim Analog Devices Edition 10.0 Free Download

I have found a good and free circuit simulator,Multisim Analog Devices Edition 10.0. As you may know that Multisim is a famous electronics circuit simulation software (circuit simulator). It's based on Electronics Workbench from the same company. I have found the free version (not the cracked version) of Multisim by chance and you may not find it on the National Instruments website. It comes with a lot of measurement tools and it's very easy to use. I use it to simulate various analog circuits. The image below shows the screen shot of the simulation of DC-Boost Converter (12V to 150V step up).


Not only analog circuit, but it also simulates digital circuit as one may call it 'Mixed-Mode Simulator'.
Some features and limitations:

• Build simulated component evaluation circuits to quickly assess behavior of over 800 Analog Devices operational amplifiers, switches and voltage references
• Examine the unit under test in the intended circuit topology with up to 25 components
• Use built-in instruments and analyses including oscilloscopes and worst-case analysis
• Swap components easily to pinpoint best design options
• Link to the Analog Devices Design Center for more online evaluation tools
• Instantly access product pages and datasheets of each Analog Devices component
• Upgrade to a full edition of NI Multisim to complete designs and transfer to board layout with NI Ultiboard

Please follow the link for Free Download Multisim 183MB

Transistor array

I am looking for transistor arrays for my LED projects as I want to reduce number of components on board. After some searches, I have found that there are two candidates for current source and sink transistor arrays as the following:
UDN2981 : 8 channels high current source MAX 500mA

ULN2003 : 7 channels high current sink MAX 500mA


I will use these transistor arrays for driving large 7-segment display panel , bright led dot matrix panel and other LED projects.

Vintage Electronics Related Magazines

There is a big collection of vintage electronics related magnazines at http://www.swtpc.com/mholley/magazines.htm .
Woww.. there were projects about stopwatches that could measure millisecond in 1968 (40 years ago).
I'm talking about these 2 projects.
- Build Ultra-Fast Electronic Stopwatch
- Build the Sports Timer

Nixie project was there too.
- All-Purpose Nixie Readout

My first PCB design

Couple months ago, I tried my first PCB design with Cadsoft Eagle free version. The software is very easy to use and there are a lot of third party libraries available.
Below is my first design. It's the display board of my digital clock. The controller module is on another board. Anyway, the design may has to be changed in order to fit a plastic enclosure. Now, I am looking for a local PCB maker and a place to buy a plastic enclosure to realize my design.