First we will join the core elements of our altialarm:
- The arduino pro mini 3,3V 8Mhz board.
- The BMP280 pressure sensor
We will directly solder these two boards, back to back. This way we get a nice, clean and small result. Don't worry about connecting the power pins of the BMP280 to ports on the arduino. This will be solved during programming.
First position the boards correctly. You can use the header pins wich come with the arduino pro mini board to help you.
Now, put a string of fine solder through the holes. Solder the top of the first hole. Now cut the bottom part of the solder.
Repeat this initially for the second hole only.
Turn the board over and solder the other side of the first two holes.
Now you can remove the header pins and repeat the process for the other connections.
Next up is soldering the programming connector to the pro mini board. First solder the connector itself. Then you'll have to solder a bridge from A6 to pin 10. Yes, A6 is where one of the programming connector pins is already soldered. You can use the solder pad of A7 if you want. Its easier and it doesn't change a thing to the end result. Sounds complicated? Just look at the pictures below:
Now, the only thing we need are the wires for connecting our project to the receiver and motor. We will be using a resistor of about 100ohms to protect our circuits from over-current due to the fact that our board voltage is not the same as the receiver's voltage.
Cut the wires to lengths about the same as this:
We will first solder the resistors to the wires. The pictures below are self-explanatory. Be aware that the resistor for the receicer-side is differently positioned than the resistor on the motor-side. First put solder on the wire and resistor. After that, join the two. This way you do not need a third hand to put extra solder.
Now connect the two black and red wires to eachother. And put a shrinktube around the in-line resistor.
You are ready to make the most critical and difficult connection of them all. Solder the red wire to the bottom of the "RAW" connection and the black wire to the "GND" connection next to it. Be sure not to make any short-circuit between them!
It's time to connect the resistors to the pins 2 and 3 of the pro mini board. Take a look at the pictures to find the most compact position. Be aware that the final shrink-tube has to fix these resistors in place. Also, let some of the wires pass over the pressure sensor. This will keep sunlight away and make sure that the sensor-hole of the sensor will not get blokked with the final shrinking tube. Alternatively use some foam of ear-plugs on top of the sensor.
Put some shrink-tube over the last resistor so that there is no more posibility for a short-circuit.
Fixate the label with some hot glue
Now fit the final shrink-tube, protecting our whole circuit. Fit the programming jumper before shrinking it so that the necessary space is created to put the jumper. Don't forget to remove the jumper before it's first use!
I did not solder the arduino programing pins. If you need them to do the programming, please solder them as well. I just held the programming pins to the pads for one time programming these boards. My board was preprogrammed before I started soldering.