Free assistance on data logger projects

Summer is finally coming to my backyard and my spring semester is coming to an end. Thinking ahead (skipping over all the final papers to grade), with the whole summer ahead of me, starting 5/15/17, I can provide some free assistance to those that are working on your data logger projects using my devices, such as the SDI-12 data logging shield and SDI-12 USB adapters.

My goal is to get you started so you can quickly work on your own after my help. I’ve used Teamviewer to remotely help people install software, test their adapters with their own sensors, and modified my Python data logging code in the past. As long as I have some time to spare, I am willing to keep providing help. I appreciate it if you could help me spread the word. I might ask you to provide a blurb such as what sensors you use and what type of project you are working on etc. as a form of exchange for my free help.

Temporary connections?

I bet once or twice in the past you wish that you could find a simple way to just hold a module with male headers like this Adafruit GPS module in the pin holes of a circuit board without soldering the pins so you can later take the module and put it elsewhere. Here I found a neat solution, wedging the module with some ESD foam. You get ESD foam pieces from buying ICs so they come for free and have some springy-ness. Then you put in between the module and the board and push in. The force from the foam will make the module form a wedge and there is enough strength to tlit the pins against the holes to make connection. Here are some photos:

The first photo shows the underside of my new phi-3 shield. The GPS module is supposed to be on the top side but unless I solder it to the shield, there is not enough space to make a wedge with the module while it is under the display. So I hang it below the shield board and stuck a piece of ESD foam between the module and the shield board. Here is a side view. You can’t see the foam, which is too dark but you do see the pins are all tilted and thus pushed hard enough to make electrical connection. I only recommend this on a temporary basis. Tomorrow the GPS module is going on another board, the SDI-12 + GPS USB adapter. I’ll solder this time.

SDi-12 + GPS USB adapter test

I was able to perform some tests on the new SDI-12 + GPS USB adapter. I don’t have the GPS module but do have an arduino shield that features the same GolbalTol GPS module so I used some jumper wires to connect the GPS to the adapter. I did tests last night and overnight. Things are looking good. Here are some results:


To get longitude and latitude, you will issue “zM!”. The return values are z(long)(lat)\r\n. The longitude and latitude are both in standard NMEA format of 100*(degree.minute). For instance, a longitude of -9412.3411 means -(94 degrees 12.3411 minutes).

To get day, month, and year, you will issue “zM1!”. The return value is again in standard NMEA format of +DDMMYY. For example, a date of +190317 means the 19th of March, 2017.

To get hour, minute, and second, you will issue “zM2!”. The return value is also in standard NMEA format of +hhmmss. For example, a time of +123507 means 12:35:07 in 24hr style so it is 12:35:07 PM for those that use 12hr style.

Sample commands (in red) and returns (in green):

Single-sensor measurement:


Concurrent measurement:


SDI-12 + GPS module

After some development, I am glad to show a prototype of an SDI-12 + GPS USB module. This module incorporates the following features:

  1. USB connection
  2. SDI-12 translator with 4 SDI-12 connections (on a single SDI-12 bus)
  3. Header for a GPS module
  4. External power connection for sensors that need more than 5V from USB
  5. External power/5V USB selection jumper
  6. You can also use other serial devices or sensors such as Maxbotix serial sonic ranger, with some modification to the firmware
  7. Both SDI-12 senors and GPS are addressed like SDI-12 sensors, for easy integration of GPS signal into your existing SDI-12 logging scripts

Here is a picture:

I ran out of GPS modules. New ones are on the way. Once I get them, I’ll solder one on an adapter and do a demo video.

Phi-panel circuit board update

Recent comments from customers interested in phi-panels have convinced me that going from the original buttons with black plungers to low-profile metal buttons was a bad idea. On my end, the low-profile buttons on the front side of the board required me to reflow both sides of the boards, something that takes a lot of time and extra effort.

So I have made a recent priority update to the phi-panels, both 20X4 and 16X2, to use the original buttons with black plungers again. I’ll be building these boards soon and post some photos.

From now on, all kits will have pre-built components on the back side. All you need to solder are:

  • Buttons
  • LEDs and their resistors
  • Connector for serial port
  • LCD
  • Buzzer

If you buy assembled version, as always, everything is assembled and ready to go.

Here is the back side of the kit board, with key components already reflow-soldered on:

Here is front side of the kit board, just a blank board:


Here is assembled unit, same as before:

Here is assembled unit’s back side:


There are many types of I2C character LCDs on the hobby electronics market. To design my new open source data loggers and Phi-3 Arduino shield, I decided to move away from the bare parallel HD44780 character LCDs and go with character LCDs and I2C backpacks (aka I2C LCDs). I found out a few popular designs and thought that I would summarize them for your convenience.

Most I2C LCDs are based on the following two ICs, all of which are I2C I/O (port) expanders:

  • PCF8574 or PCF8574A
  • MCP23008


Both ICs have 8 I/O pins. MCP23008 is more versatile but that is irrelevant to simple applications in LCDs.

Adafruit designed an I2C LCD backpack and Arduino LCD shields based on MCP23008. There are compatible devices sold on ebay. I can’t tell without seeing the sample code to decide whether an ebay seller is actually selling a compatible product. But if you do want to get one on ebay, make sure you find their library code and confirm that the library contains Adafruit’s names. Libraries you find from ebay sellers are likely out of date though. One good thing is that the compatible ones are very likely using the same pin assignments as Adafruit’s so it’s easy to get it to work once you get the library installed.

FM (Francisco Malpartida) designed an I2C LCD backpack based on PCF8574. There are lots of compatible devices sold on ebay and they don’t have the same pin assignments! This creates issues when you are making purchases thinking that they have certain pin assignments. The pin assignments refer to which PCF8574 pin is connected to which HD44780 display pin. Also the I2C addresses are all different. I don’t mean one might have an address of 0x3F and another might have 0x3E. What I mean is that one might have 0x3F and another one may be 0x20. There is no way to set one display that has address 0x20 to address 0x3F! PCF8574 has address space of 0x20 to 0x27. PCF8574A has address space of 0x38-0x3F. Most common addresses I’ve seen are 0x20, 0x27, and 0x3F, with the latter two sharing pin assignments that are different from the ones with 0x20 address. Most of these displays allow you to cut traces or solder pads to change addresses. Why would you if you don’t have multiple LCDs?


Adafruit has its own library Adafruit_LiquidCrystal. This library is decent. It can take different pin assignments as parameters. On the other hand, it is a different library than Arduino’s included LiquidCrystal library. So code you wrote for LiquidCrystal library may need some change when you switch to an Adafruit compatible I2C LCD.

FM wrote a library New LiquidCrystal. This library is pretty good. You can use a number of different LCDs including parallel HD44780 LCDs, I2C LCDs using PCF8574, LCDs using shift registers etc. A nice feature is that there is a base class LCD so regardless what actual type of LCD you are using, as long as it’s supported by this library, it works the same way on the software level as another supported LCD.

Since not all PCF8574/74A I2C lcds have the same pin assignment, or even back light polarity, using the correct definition will be crucial. I found the following three definitions. Each seems to work with the particular I2C address, although there is no relation between I2C address and how the pins are assigned (by circuit designer):

The first two work on backpacks that look like this:

Notice that only the address is different. Pin assignments and back light polarity are all the same.

LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Blue potentiometer with back light jumper.

LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Blue potentiometer with back light jumper.

The last definition works on backpacks that look like this:

Notice that pins are very different and back light polarity is negative.

LiquidCrystal_I2C lcd(0x20, 4, 5, 6, 0, 1, 2, 3, 7, NEGATIVE); // Tiny mental potentiometer no back light jumper.


In case you can’t determine the address or pin out, say none of the above definitions work, but you’re sure the IC is PCF8574/74A, you should first scan the I2C bus for the address, and then use your meter to map out the pin assignments, and then use your definition. The lcd constructor has the following parameters: lcd(add, En, Rw, Rs, d4, d5, d6, d7, Bl, Pol).

Here is the I2C scanner I use by Tod E. Kurt:


Open source data logger videos

Open source data logger videos:

Quick demo:

Features introduction 1,2,3

Assembling the logger


Phi-3 shield videos

Here is a video of me navigating through the alarm clock program’s menu:

Here is a video of me explaining the components of the shield:

Here is a video of me explaining the different kits you can buy:

OK one more assembling modules on the shield:

Phi-panel 20X4 kit available again

Sorry the Phi-panel 20X4 panel kit was unavailable for a while. I’ve made some updates to the board. Here is a picture of the board:

This is the back side:
2017-02-28-20-42-57Notice that the push buttons are all surface mount buttons. The have low profile and are a bit different from the old buttons with a thicker profile and black plunger.

Also most other components are surface-mounted.

The kit will have all surface-mounted components pre-assembled but the following parts still need your assembly:

LCD’s pins, 6-pin female header on back side, and the speaker. You also have to adjust the potentiometer to get proper contrast.

Open source data logger

I have been designing data logger for a number of years. This is my answer to lots of data logging needs. An Arduino Nano-based open source data logger:


The logger provides the following features (in green) including features of Arduino Nano (in black):

Microcontroller Atmel ATMEGA328P
Power 5 V via USB or 2X AA battery (internally)
Digital I/O 10 (4 PWM output, other Arduino pins used internally)
Analog Input 4 10-bit ADC (8 on ATMEGA328P, only 4 brought out)
DC Current per I/O Pin 40 mA max
Flash Memory 32 KB of which 2 KB used by bootloader
EEPROM 1 KB on ATMEGA328P, 32 KB on real-time clock breakout board
Clock Speed 16 MHz
MicroSD card 32 GB maximum
Real-time clock Temperature compensated (DS3231)
ADS1115 4-chn 16-bit differential ADC with up to 16X programmable gain
LCD 16 column by 2 row character LCD with back light on/off control
Input Rotary encoder with switch (when shaft is pressed)

Table. Specification of Arduino Nano and the rest of the modules.

Another photo:


As you can see, the logger incorporates a number of breakout boards instead of including these ICs on a single circuit board. More to come…

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