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power-bank-sensor-node

Tutorial how to build a USB-chargeable temperature / humidity / pressure sensor node in a power bank case which transmits the data via 433MHz to a receiver whose serial protocol is MySensor compatible.

Example

Here is an image of an earlier version of the sensor node:

Click here for a high-res picture

Prequesites

Here is a list of things to buy:

  1. Arduino Pro Mini 8MHz, 3.3V Ebay
  2. 433 MHz sender module Ebay
  3. BMP180 pressure sensor Ebay
  4. DHT22 humidity sensor Ebay
  5. USB cell phone charger Ebay
  6. 16340 rechargeable battery Dealextreme
  7. Optional: USB plugs & DS18B20 tempereature sensors Ebay

Schematic

Note: The programming pins of my Arduino seem to have a different order.

Howto

Step 1: Remove unecessary and power hungry parts of the Arduino

Here is the Arduino Pro Mini I used (left picture). First unsolder the reset button (right image, green circle on the left), the power indicator LED (circle in the middle) and the step-down converter on the right.

Step 2: Reduce the size of the Arduino

We have to shorten the Arduino so it fits together with the battery into the power bank case. So cut it with a saw between pin 11 and 12 so that pin 12 still remains usable as seen on the left picture. The result can be seen on the right.

Step 3: Remove the pins of the 433MHz sender

The sender comes with pins that are not needed.

Step 4: Add programming header

Add a female pin header to the Arduino to program it later. The free pin on the right is the second ground pin on the row.

Step 5: Create sender adapter

To connect the sender to the Arduino create an adapter as seen on the left picture. Solder it to GND, VCC and pin A3.

Step 6: Add some cables

Solder two (half blue) cables to the free Arduino GND pin right of the programming headers (green circle at the top). Also add cables to Arduino pin A4 (half green wire) and Arduino A5 (green wire) (green circle in the middle). Remove the plastic connectors of the sender adapter and cut away one section. Then add it on the to straight pins and push it down to the Arduino board as seen on the right picture (green circle)

Step 7: Add pull up resistor and connect sender

Solder a 4.7kOhm resistor to Arduino pin 4 and 7 as seen on the left picture (green circle). Then add the sender module on the top connected to the adapter as seen on the picture.

Step 8: Add pin header for the BMP180 sensor

The VCC of the BMP180 sensor will be connected to Arduino pin 5. Therefore a long pin header is soldered to Arduino pin 5 as seen on the picture below (green circle).

Step 9: Prepare BMP180 sensor

Put a piece of tape on the bottom side of the BMP180 sensor as seen on the right image.

Step 10: Add BMP180 sensor

Cut the green wires and one of the blue ones as seen on the picture. Then solder the BMP180 as seen to the pin header (Arduino pin 5), GND (half blue wire), A5 (green wire) and A4 (half green wire).

Step 11: Add DS18B20 connector

Solder a long (10cm) wire to Arduino pin 6 as seen on the left picture. On the back side of the Arduino connect pin 6 and pin 7 as seen on the right picture (I forgot it when taking the pictures, that's why it shows a later step).

Step 12: The USB power bank cellphone charger case

In general any case like this will work. I found there are small differences between the same looking cases on ebay. Especially when it comes to idle power consumption it might be interesting for this project. As a reference: A "good" case consumes about 0.025-0.050 mAh when idle without anything connected.

Step 13: Prepare power bank case

The battery holder has to be shortened to fit the 16340 battery. Unsolder it and shorten it as seen on the second picture. Then solder it again to the PCB of the charger (third picture). Check if the battery and the Arduino fits into the case. The result should look like on the most right picture.

Step 14: Prepare DHT22 sensor

Cut off the upper part of the DTH22 sensor if you like. You could use the loop to fix the case somewhere but the sensor will not fit nicely onto the power bank case. The result is shown on the right picture.

Step 15: Attach DHT22 sensor to power bank case

Pierce the pins of the DHT22 sensor through the case by heating them up with the soldering iron as seen on the left picture. Beware that there has to be enough space for the case cover. Finally, glue it to the case (right picture).

Step 16: Add power cables for the Arduino

Solder a blue cable to the positive pole on the charger PCB and a half blue cable to the negative pole of the charger PCB as seen on the left picture. Cover it with shrinking tube and attach pin headers to it as seen on the right picture.

Step 17: Connect DHT22 sensor

Solder a half brown cable to Arduino pin A0 (data) and a brown cable to Arduino pin 13 (VCC) as seen on the left picture. Then connect the DHT22 sensor with these cables and the half blue cable (GND) as seen on the right picture.

Step 18: Fit everything into the power bank case

Fit everything into the power bank case as seen on the left picture and connect the power connector as seen on the right picture.

Step 19: Connect DS18B20 data cable

Solder the long, orange cable to the lower USB data connected (the one close to the USB ground).

Step 20: Add seperator and attach antenna

Cut a piece of paper as seen on the left picture and place it between the battery holder and the Arduino. Solder a 17.5cm long wire to the antenna pin of the 433MHz sender as seen on the right picture.

Finish

Assemble everything, it should now look like on the pictures below.