How to make car audio/stereo (mp3/bluetooth/radio) for $10

[audio (mp3, bluetooth, radio) module]
 

In this article I will show you how to connect this mp3 bluetooth audio module to a car.

How to make digital weather station with wireless outdoor sensors

Fig. Block diagram of a weather station

1. Sensors

I used 3 sensor modules which can be acquired via ebay or aliexpress. It seems they are cheap Chinese clones of well known sparkfun/adafruit modules. Also I made a simple sensor to monitor battery voltage. (Someone should keep a Li-ion battery above 3V level.) You can easily find arduino libraries for these modules. So modules can be used at once. But keep in mind a "chinese clone" sensor can use a different I2C address. So you may need to run an arduino script that called I2C scanner to identify these addresses and then change a device I2C address constant in a library header file to guarantee correct work the library with the module. 

I used the following devices