The hardware of data logger is quite simple to build, because most elements are breakout boards and the most complicated part to build is the capacitive touch pad. Here a list of all required parts:
- Adafruit Trinket Pro 5V
You can also use an Arduino Nano, or Arduino Pro Mini or even use an Arduino Uno. If you like to use my software without changes, the only important part is the ATMega328P microcontroller, running at 16MHz.
- Adafruit PowerBoost 500
This is a combined power source and changer for lithium ion batteries. There are lots of alternatives to power your device, the simples one is by using alkaline batteries.
- ChronoDot Real Time Clock
The ChronoDot contains the Maxim DS3231SN chip. You can use any other breakout board which contains the same chip, or even use the chip directly.
- AM2302 (wired DHT22) Temperature/Humidity Sensor
I use this version of the DHT22 humidity and temperature sensor which comes in a small case. There are other versions of this sensors you can use.
- Adafruit Sharp Memory Display Breakout
This breakout board from Adafruit contains all required components to run the really cool memory display from Sharp. I use this display because it requires almost no power to run.
- Adafruit Standalone 5-Pad Capacitive Touch Sensor Breakout
This breakout board provides everything you need to create a nice and stable capacitive keypad. The chip on this board is very smart and only creates a signal for the pad with the “strongest” touch. If you use the AT42QT1070 chip directly, you could even connect it via I²C.
- Universal Qi Wireless Receiver Module
The stripboard connects all components. For this project it has to be minimum 9cm × 6cm, but the size depends on the components you use.
- 10 kΩ Resistor
This resistor is used as pull up resistor for the sensor.
- 2x Slide Switch on-on
I use the 600A-611-M2R from Taiway for the power switch and the SS12SDP2 from NKK for the charge connection.
- Case with Transparent Lid
I used the Fibox Piccolo PC C 65 T.
- Copper Tape
- Crimps and Crimp Socket
I use them to attach a connector to the sensor and to make connectors for the battery, Qi receiver and key pad.
- Various Pin Headers
The pin headers are used to connect the components to the stripboard. I soldered the components directory to the stripboard, if you plan to reuse the components in other projects, you should add female pin headers to the board.
- Various Wires
I use 0.50 mm²/ø0.20 mm wire in many colours to make the connection on the stripboard and a rainbow coloured flat cable to make connections to components with multiple wires.
Adafruit Trinket Pro 5V
I really love this tiny microcontroller board. It is cheap and has the same microcontroller from the Arduino Uno, the ATMega328P. There is a very flexible voltage regulator on this tiny board, so you can even use a 12V power source and almost all important pins of the microcontroller are available as pinouts. Thank you Adafruit!
If you plan to make a small device, you have some alternatives like the Arduino Nano or the SparkFun Arduino Pro Mini. If you have no size limits, the whole project also works perfectly with an Arduino Uno.
Adafruit PowerBoost 500
This is a nice lithium ion charger and power source. First it converts the low voltage (~1.8V) from the battery to 5.2V which is perfect to run the project. You can solder a USB port on the breakout board to use it as power source for other USB devices. I connect the Qi receiver to this component to allow wireless charging.
You can use any other kind of power source and connect it directly to the Trinket Pro, which will regulate the voltage and provide a stable 5V output for all other components.
ChronoDot Real Time Clock
The ATMega328P has no real time clock, so you need an external one to provide the software with the current date and time. The ChronoDot is a nice breakout board with the Maxim DS3231SN chip. This chip is a very precise real time clock, it is powered by a CR1632 battery to keep the correct date and time while the device is turned off. The drift is less than a minute per year, which is nice because you virtually never have to adjust the time once it is set.
There are many alternativ breakout boards featuring this chip. You can also use boards with the DS1307 chip which should work with my software too.
The AM2302 is a precise humidity and temperature sensor. It is a wired version of the DHT22 sensor in a white case. I use this sensor because of the high precision and simple use. It uses only one wire to transmit the data using short and long pulses. The only catch is it is a very slow sensor and you need precise timing to read the data from the sensor. You can use any other DHT22 variant with my software.
Adafruit Sharp Memory Display Breakout
This is an amazing display. It uses almost no power and stores the state for each pixel. So you only have to transmit the changed areas of the screen. While there is no change, you only have to toggle a flag which is called VCOM at least two times per second. The Adafruit breakout has a voltage regulator and all required capacitors which are required to use this display.
Adafruit Standalone 5-Pad Capacitive Touch Sensor Breakout
I could use the analog inputs of the ATMega328P as capacitive touch sensors, but if you ever tried, it is not easy to use them in a stable way. This breakout board using the AT42QT1070 chip to sense the touch input. The detection is very precise and works ever trough the 3mm transparent plastic lid of the case.
The software just requires a signal on the five pins of the microcontroller, so you have many alternatives to control the device.
Read how all this parts are used to build the hardware.