In this project there are actually 3 chargers combined in a single PCB, each charger having an output voltage of 4.2V. You can cascade them to become charger fit for 2 or 3 cels Lipo pack. The transformer used is 3 x 8 VAC. As more and more devices are powered with LiPo batteries such a charger could come handy some day.
DIY LiPo Charger: [Link]
You all know that opto osolator boards are used to pass signal between circuits without connecting them electrically. They are great for eliminating noise problems, or to connect circuits that have different voltages.
The opto isolator is very easy to use. Since it just passes signals through it, you just hook it up between the two different devices you want to communicate. Additionally, you will need to properly hook it up to each devices power supply. The device is intended to isolate the circuits electrically, so each side needs to be powered independently.
T-Clock is a demo-application for Philips LPC2000 ARM7TDMI controller with a KS0108/KS0107-based graphics-LCD (128*64 pixels), DCF77 time-receiver and one wire bus (for DS18x20-Temp.-Sensor).
The time and date are received with a DCF77-receiver-module. The DCF77-signal is transmitted from a station near Frankfurt/Main, Germany and can be received all over Europe, North Africa and the Middle-East. Please visit www.ptb.de and ask google with “DCF77″ for more information. In times when the DCF77-signal is not available (i.e. thunder and lightning near transmitter) the RTC of the LPC-controller is used to drive the clock.
The clock also display the temperature measured trough a DS18x20 family sensor. he sensors provide the temperature in digital form on a One-Wire-Bus. The Maxim Web-Site has a lot of information on the One-Wire-Bus.
The whole project should cost you about 100 Euro’s, not cheap but a very good and interesting project for ARM microcontrollers.
T-Clock An ARM7 Controlled Blue LCD Clock: [Link]
This schematic is ment to digitally display the output of an electronic Swissflow SF800 flow sensor. This sensor puts out an open collector square wave signal (like a fan RPM monitoring signal) between 50Hz (=0.5 liter/minute) and 2000Hz (=20 liter/minute).
By dividing the measured frequency by 10 and putting the decimal point at the right place you get directly a display in liter/minute. I don’t use the first digit output (output D) from the 74C925 to obtain a display of 10 to 9990Hz or xx.x liter/minute.
3-Digit Frequency Meter: [Link]
I wanted to build an etching tank since i first saw one in an article on Make Blog. It was fun to make it and it will sure speed-up my PCB making process. The main thing that i wanted to achieve with my etching tank was to keep it thin so it holds up smaller amounts of etchant, it’s better this way because i need to store and work with smaller quantities. My finished tank holds 1,5 L of liquid when full.
In the article on Make the author made he’s from acrylic magazine holders. I chose to make mine from plexiglas. I got this 1500x1000x3 sheet for about $15 and now i got enough left to make cases for other projects. When working with plexiglas there are several methods of cutting it which include sawing it, cutting it with a hot wire or cutting it glass style. I used the method glass style which means you make repeated scratches on the same path using a sharp cutter.
Depending on the thickness of your plexiglas you have to make more or less deeper scratches. You’ve reached the desired scratch depth when you try to bend the plexiglas and it just snaps along the line. I would of shown you pictures from the making process but unfortunately i accidentally erased them 
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For gluing i used a PVC adhesive from Bison, it’s supposed to be used when gluing PVC pipes so i figured it should work on plexiglas too. The nice thing about it is that is leaves a nice transparent finish. After gluing i left it to harden for 24 hours.
Before assembling the etching tank make sure you’ve drilled holes for the heater and the hose.
On my DIY Etching Tank i also used a heater(an old aquarium heater that i used when i was into aquariums) to heat the etchant because heating it makes the process faster. Besides the heater i also added an aquarium pump that will agitate the liquid thus making the process even faster.
The parts used in the making are:
Total: $41 . So with a little over 40 $ you can make your own etching tank
Here are some pictures with the tank being tested with watter:
