Version: Pro Mini

Design:

​The Pro Mini is the smallest of the Arduino boards used in this project. It also has the potential to be the most power efficient. This makes it a great choice if you really need to stretch your batteries, or have a very strict space requirement. Due to its' size though, it can be a bit difficult to wire / work with as everything is so compact. The wiring and assembly is basically the same as the Nano version, using the same parts and wiring to the same pins. 

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You will need an additional piece to work with the Pro Mini though. The Pro Mini does not have any USB connections on the board itself (saves space and some power) so instead you will communicate with the board via a Serial communicator breakout board (FTDI board). This will act as a communication bridge between your computer and the Pro Mini. There is one linked in the Parts section below, but just make sure whatever one you get works with the Pro Mini you have (i.e. that you have a breakout board that will work with the correct voltage as the Pro Mini). 

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Last note on the Pro Mini: the layout / wiring presented here is for a 5v version of the Pro Mini. This is done just to keep it comparable to the other versions. But the nice thing about the Pro Mini is that it also comes in a 3.3v version, that has the exact same layout as the 5v (more on that at the bottom of this page). If power savings are the most important thing in your design, then the 3.3v Pro Mini is your best choice. Just make sure that all your components (RTC, SD reader and the Sensors you plan on using) can all operate at 3.3v, if you wish to power them via the Pro Mini itself. The parts listed below would work with the 3.3v version; and the connections and code used would also work too. ​

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Parts:

1. Pro Mini Board 5V (or any of the many clones available)

2. RTC (or any of the DS 3231 RTC breakout boards)

3. SD reader (or any other you'd like)

4. DC-DC converter / voltage regulator (or some other way to control incoming voltage)

5. Serial Breakout Communicator (there are tons of options out there) 

6. Micro SD card (FAT 16 or 32) and appropriate coin battery for RTC

7. Some 22 awg Wire

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After this you will need whatever sensors you wish to use, along with some wiring to connect a power source (battery, wall, solar, etc).

 

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Assembly:

​The wiring for this set up is the exact same as the Nano version. But you will need to solder in some header pins along the 'front' of the Pro Mini, so that you can slot in the Serial breakout board when you want to communicate with the Arduino. Specifically you will need to solder in headers along the pins; Blk / GND / VCC / RXI / TXO / GRN.  These 6 pins will interface with the serial communicator board. (Linked here are some additional documentation if needed)

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For the SD reader: Solder some length of wire to the following pins and connect to the Pro Mini as follows - 

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​3v (or VCC) pin of SD - to - VCC of Pro Mini*

Ground of SD - to - Ground of Pro Mini

CLK of SD - to - pin 13 of Pro Mini

DO (or MISO) of SD - to - pin 12 of Pro Mini

DI (or MOSI) of SD - to - pin 11 of Pro Mini

CS of SD - to - pin 10 of Pro Mini

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For the RTC Module: Solder some length of wire to the following pins and connect to the Pro Mini as follows -

 

​3v (or VCC) pin of RTC - to - VCC of Pro Mini*

Ground of RTC - to - Ground of Pro Mini

SCL of RTC - to - A5 of Pro Mini (or SCL pin)

SDA of RTC - to - A4 of Pro Mini (or SDA pin)

SQW of RTC - t0 - pin 2 of Pro Mini

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Once everything is connected, you should be good to go. Just make sure you add in the micro SD card, and appropriate coin battery for the RTC module. 

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*Again, like the Nano, the power pins of the SD and RTC modules will be sharing a source from the Pro Mini board. The VCC pin of the Pro Mini board will output whatever voltage is used internally for the Pro Mini (so either 5v or 3.3v depending on the board you are using). Just make sure that if you are using a SD or RTC that needs a specific voltage that you've matched that up correctly with the board. Also, like the Nano, you should tie the grounds and power pins of the SD and RTC together before connecting them to the Pro Mini. 

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Adding Sensors and Uploading Code:

To add sensors, simply follow the wiring diagrams / design provided by the manufacturer. Refer to the Sensors page of this site for further guidance in selecting sensors, and wiring them in to your DIY system. 

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For code, you can find some simple code for this system at the linked GitHub page. Under the "Version Pro Mini" folder you will find a "Blank" code that is a generic logger code that works with this setup. Make sure to add in the additional code needed to power and record your sensors, and modify the timing interval. If you are totally new to Arduino, I recommend reading / watching some of the many amazing online tutorials for getting started with connecting your Arduino and uploading code. Minimally, you'll need to download the Arduino IDE (code interface) and probably read through the "Getting Started" documentation. Also don't forget that the Pro Mini will need the additional serial breakout board to communicate with your computer. Make sure you download any drivers needed for communication. 

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​Arduino Pro Mini Data Logger Specs:

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Internal Operating Voltage:  5 V

Digital output pins power: 5 V and up to 40 mA

Base Operating power consumption - 5v version: 16 mA

Lower power sleep power consumption - 5v (average in my tests, with LED's removed): ~4 mA*

Dimensions of board: 2 cm W x 3.2 cm L x 1 cm T

With the components added and stacked on top of the board, overall height is ~ 5 cm T

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*This 4 mA draw is mostly coming from the DC-DC / External voltage regulator linked in the design. There are more power efficient voltage regulator boards out there; so using one of these would be a better / more power efficient system. For example, you will get a sleeping power draw of less than 1 mA if you supply the board with 5v directly via a power supply (thus by-passing the voltage regulators)

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A Note on Power:

​For all the system in this website, you will need to supply them with some sort of power. All the Arduino boards used here are 5v boards, which means that at a minimum they need a 5 v power source supplied. The Pro Mini is more particular than the other boards in that, it only operates at one interval voltage (5v or 3.3v). For optimal power efficiently (lowest current draw) I recommend suppling the 5v Pro Mini around  5-5.5v directly to the Arduino board via the VCC / Vin pins. By doing this, you limit the need for the Arduino to lower the voltage coming in, which is a more efficient way to power the board. Also, in my own experience, the Pro Mini Vraw pin / onboard voltage regulator (the input pin for voltage greater than 5v) struggles to lower incoming voltage. Usually I end up feeding 5v directly to the Vin of the Pro Mini to ensure everything gets the correct power. 

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If you wish to deploy these without any connection to land, I recommend using some rechargeable batteries that are 6 - 12 v. Run those batteries through the DC-DC converter / external voltage regulator and set the incoming voltage to the Arduino to 5 - 5.5v. DigiKey is a great resource for finding various battery types. If you are running off of solar or some sort of 'land' power, then I still recommend going through a converter to regulate the voltage, but you won't have to be as concerned with power efficiency. One note though: many of the more inexpensive DC-DC converters will end up consuming more power by itself then the rest of the logger uses while in sleep mode. If you really need to stretch your system life, I recommend looking for efficient power converters, or feeding the power source directly to the Arduino. Just be aware that directly feeding a higher voltage source (6v or more) to the Arduino will cause the Arduino to generate heat. This may cause the system to overheat, especially if using sensors that pull a lot of power. 

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If you want to learn more about conserving power with regards to Arduinos, there is a really good blog post that runs through all the different coding and physical things that can be done to lower the power consumption of the boards, as well as some documentation from Arduino themselves.  For the designs on this site, the Arduinos are being put to sleep in-between measurements, and all LED's are removed from any of the boards used (including breakout boards with the sensors). Also removed from the Pro Mini version is the onboard voltage regulator chip. This is not the most power efficient way to control voltage on the board. Since we are running our incoming power through a converter / regulator that is controlling the incoming voltage, we no longer need the on-board regulator. To remove, you can either de-solder the chip, or just use needle nose pliers to carefully break it off. Also as stated above, the external regulator used in this build isn't the most efficient one available. It just happens to be a relatively inexpensive one that is readily found on Amazon / other online markets.  

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5V vs 3.3 V Pro Mini:

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Base Operation power consumption - 3.3v version: 4.5 mA

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​For the Pro Mini, you can see that the 3.3 v version really is significantly more power efficient than anything else used in this site (base operating current draw is 4.5 mA vs 16 mA for the 5v version). If length of battery use is your main need, then the 3.3v Pro Mini is your best choice overall. The SD and RTC used in this build will also work with the 3.3v version, and they would be wired in the exact same way. The code used in this build would also work. If you really want to push the limits of power savings; this website / project goes through some of the modifications you can do to really stretch the power usage of these types of systems. Also using a efficient external voltage regulator to supply 3.3v directly to the board (and removing the onboard voltage regulator from the 3.3v Pro Mini) would get you to about as power efficient as you can get for any of these DIY systems. ​

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