Data Loger

An arduino based low cost environmental data logger.

Components:

Arduino pro mini 3.3v  ~ 2€

SD card module ~ 1.25€

RTC Real Time Clock Module ~ 1.25€

18650 battery* ~ 2€

You can also find 18650 batteries from an old laptop.

Sensors

BME280 ~ 5.5€

or

HTU21 ~ 4.5€

Other sensors
AM2320 Digital Temperature Humidity ~ 3€
MQ-135 Air Quality Sensor ~ 2.5€
TEMT6000 Light Sensor ~ 2€

Schematics

Simple LED flasher

I made this simple LED flasher as a safety blinker for my bicycle.
This circuit it only consists of two transistors, two capacitors and four resistors. You can control the flash rate by changing the size of the resistors or the capacitors.

Street motorbike LED Turn Lights