Difficulty level: 4/10
Step 1: How It Works: Schematics and Simulation
Because my phone charger provides 6.75V on no load attached, I also built a voltage regulator section from a L7805 and 2 capacitors.
I have been also simulated the system in Proteus.
Here are the files for simulation, and the schematic in eagle:
Step 2: The Parts
For the main circuit: 2x pushbuttons, male and female pin headers, 2x 2pin screw terminals, 2x 10k resistors, 2x 10µF electrolytic capacitors, 1N4007 diode, bc546 NPN transistor, 5V relay (like SRD-5VDC-SL-C), 14 pin IC socket, 8 pin IC socket, SN74HC14N, ATTiny85, HC-06 bluetooth module, Copper clad laminate board (70x50mm or larger)
For the voltage regulator unit: 2x 10µF, LM7805
For the PSU: take apart an old phone charger, or buy a 5V adapter
For enclosure you need an approx. 20 cm x 10 cm box
You can buy these parts from this ebay collection, but if you have I recommend to buy this parts from your local electronics shop
For push buttons I recommend two big one to mount to your enclosure.
Step 3: Programming the MCU
Make sure you buy an ATTiny85, not ATTiny45 or others, because the ATTiny85 has got 8 kbytes of flash memory.
Step 4: Test Everything on the Breadboard
After you programmed the MCU, test the circuit on the breadboard to make sure everything works correctly.
You can use an LED instead of the relay, transistor, flyback diode and light bulb.
Step 5: PCB Etching
Download and open the PCB design attached to Step 1. In the layer settings only select Buttom, Pads, Vias and Dimension. Print to photo paper. I'm using thin A4 sheets. Cut out the printed design and put to the copper clad laminate sheet cut to size, cleaned and polished. Then use your iron to transfer the toner to the plate. To make sure to transfer all the toner you can scour the paper with something. This procedure takes about 5 minutes. After that throw the plate with the paper to cold water. If we did everything correctly the paper shoud come down intact without any toner on it. Throw the PCB into ferrit chloride and wait about 10 minutes to etch corretly. Then you can drill the holes on i t
Step 6: Soldering
Now solder the components to the pcb. Male pin headers to the place of the buttons, female to the place of the bluetooth module like on the picture. And don't forget the ic sockets.
Then solder cables to the buttons and female pin header as the picture shows.
Make the voltage regulator unit soldering the caps on the IC and covering with shrinking tubes following the schematic in Step 1. Be careful with the polarity of the capacitors.
Step 7: Putting It All Together
Drill holes for the buttons on the enclosure and put everything in it. Connect the input of the voltage regulater unit to the power supply and the output in the power terminals of the circuit. Connect the 2 switching wires to the other screw terminals. Then connect the 2 input wires of the PSU to the wall outlet. Be careful with connections because of high voltage and don't forget to use shrinking tubes as often as you can!!!!
For android app I recommand this: https://play.google.com/store/apps/details?id=com.giumig.apps.bluetoothserialmonitor
It's very easy to use, just connect to the bluetooth device in switch mode, set the on to 'n' character, and the off to 'f'.