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:

I2C LCDs

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

Hardware:

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 Libraries you find from ebay sellers are likely out of date though.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?

Software:

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.

Detection:

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:

https://github.com/todbot/arduino-i2c-scanner/

 

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:
2017-02-28-20-42-47

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:

ospl-th-on

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
SRAM 2 KB
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:

red-version-assembled-lcd-removed

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…

Phi-shield revised and released

phi-3-shield-on-in-hand

It has been a while since I gave the phi-shield a major revision. I’ve been working on this for a while and now I am releasing the Phi-3 shield. This shield continues to support user interaction with LCDs and buttons. Here is a list of the features:

The following hardware are provided by the shield:

  • 20X4 LCD with back light on/off control
  • Six buttons (up/down/left/right/B/A)
  • Two LED indicators
  • Speaker
  • MicroSD card slot
  • Real-time clock (DS3231)
  • EEPROM (32KB 24LC256)
  • Connector for Adafruit Ultimate GPS module or Bluetooth module
  • Stacking headers for easy access to all pins.
  • Recessed board right edge for easy access to MEGA’s 18X2 pin headers on the right side.
  • Reset button

phi-3-shield-lcd-side-by-side

The following software functions are provided by various supporting libraries:

  • User-selectable menu (LCD + buttons)
  • Number and text entry (LCD + buttons)
  • Scrollable long text (LCD + buttons)
  • Date and time (DS3231 or GPS)
  • Location (GPS)
  • Data and configuration storage (MicroSD card and EEPROM)
  • Playing simple tones (speaker)
  • Indicators (LEDs)
  • Wireless connection (Bluetooth module)

phi-3-shield-lcd-removed-annotated

There are three tiers of Phi-3 shield kits: kit0, kit1, and kit2, none of which includes a GPS module. The kits are immediately available. Buttons with color caps as pictured will be included while supplies last.

Here is the Phi-3 shield’s own page. There are links on the page to make purchases. Or you can visit the BUY page to see what stores carry this shield.

Phi-3 shield

Video demonstrations will be available next week. Meanwhile, the support of Phi-2 shield will remain. If you need Phi-2 shields, I have them available.

phi-3-shield-bottom-rtc-lcd-wire-removed

Sensing temperature

Sensing temperature seems to be an easy enough task using Arduino etc. You take a thermistor that changes resistance with temperature, such as a 10K ohm thermistor, which has a nominal resistance of 10K ohm at 25DegC. You take a fixed-value resistor, say 10K ohm, and make a voltage divider with the thermistor. You use analog input to sense the voltage of the divider and calculate the resistance from the voltage, then temperature from resistance. You can call this fixed resistor a serial resistor since it is in series with the thermistor. The following diagram is a voltage divider. The R_known is the fixed-value resistor. The R_unknown is the thermistor. A 5V voltage is applied to the resistors and a “sense” pin is sensing the divider voltage.

voltage divider

Then why am I wasting time to reiterate this simple task? Consider, the fixed-value resistor is made of a carbon film. What does carbon do at different temperatures? It changes resistance! So the “fixed-value” resistor you have is no longer fixed in value, especially if you live in places with temperature extrema, like where I live. I can get below 30DegC and above 30DegC outdoors in winters and summers. When you consider temperature, you can easily span almost 60DegC temperature range from a 25DegC nominal room temperature, where the fixed resistance values are specified, to a -35DegC where your data logger is logging data. If your fixed-value resistor doesn’t come with a temperature coefficient, well, it should! You can assume maybe 200ppm/DegC. This means 200 parts per million change of resistance per degree C. With -35DegC at 60 DegC below nominal temperature, you are looking at:

200*60/1,000,000=0.012=1.2% resistance change

This change of resistance could result in several percent of temperature reading error. The exact relation requires some calculus maybe I can discuss if there is interest. So you can expect to have several DegC or more error.

Here is what I noticed by driving two cars:

They both exhibit this behavior: After I park the car outside for several hours in cold temperature, I start the car, the “outside temperature display” says it is something like 10 degF. After several minutes, the temperature starts to drop to lower values.

Car 1: there is a few DegF drop. Say it will say 10DegF at startup, then it will say 7DegF after a few minutes

Car 2: there is as much as 15 DegF drop. If is says 10DegF at startup, it may say -5DegF after a few minutes.

Car 2 is newer than Car 1 but both cars are newer cars.

So my thought, although not tested (that might require disassembling the car computer), is that, the newer car is using a lower-grade serial resistor with the temperature sensor (thermistor) than the older car. This serial resistor must be inside the cabin, on the car computer’s board. When it is cold, its value increases considerably to maybe a couple percent higher than the nominal value. This trend of increasing resistance with decreasing temperature is shared between carbon and semiconductor (thermistor). So the effect of thermistor increasing resistance with decreasing temperature is countered by the effect of carbon increasing resistance with decreasing temperature. Then once the engine warms up the cabin enough, the fixed resistor warms up and the temperature display changes.

So how do you counter this effect i.e. temperature coefficient of fixed resistor? You can buy better resistors with less temperature coefficient, such as 20ppm instead of 200ppm. You will drop that effect to 1/10, which will be able to provide you the right accuracy. But these resistors aren’t exactly cheap. For instance, the 10K resistor I used as serial resistor in one of my designs has 10ppm/DegC:

279-RN73CA-10K

This resistor is about a dollar each. It is not only low in temperature coefficient, but also high in precision, 0.1% (i.e. it is at most 0.1% off from 10K when measured at nominal temperature)

 

When I don’t need this precision, just need a ~10K pull-up resistor for reset pin, I use this one:

652-CRT0805FZ1002ELF

This resistor is only 20 cents but it’s not too bad. 1% precision and 50ppm/DegC. I suspect the car 2 has something like this or even a bit worse! A 5% precision 200ppm resistor is only 10 cents. What would I use if I needed to make lots of cars?!

Python code for multiple SDI-12 sensors

As you probably know, the SDI-12 sensor logger code in Python can only log one sensor at a time. It is not a hardware limitation. I wrote the logger code as an example of how to do logging with the SDI-12 adapters and Python. To make sure people don’t have the wrong ideas that you can ONLY get one sensor logged, I have been working on the logger code for the past couple of days and have increased the number of sensors from one to any number you need. The improvement is backward compatible with the configuration file for Raspberry Pi logging, in case you wonder. All that is changed to the user interface is the prompt:

Original prompt:

‘SDI-12 sensor address: (0-9, A-Z, a-z)’

New prompt:

‘Enter all SDI-12 sensor addresses, such as 1234:’

 

So if you have 4 sensors you want to log together, then just enter all their addresses in a string, such as 1234 and hit enter. All sensor inputs will be saved to log file and sent to sparkfun’s data server. The only limitation on the code now is the sparkfun data server stream. The server stream is set up to only take 6 values so the logger code will send the first 6 values from all sensors to the server. If you wish to lift this limitation, you should create your own stream and set up as many values per data point as you need, and modify the logger code (see the magic number 6?).

Below are some sample data logs:

2/3/2017  12:15:25 AM 1 1.11 26 z 5.09419 5.09381 0.24388 5.09419
2/3/2017  12:15:56 AM 1 1.11 26 z 5.09325 5.0925 0.24388 5.09306
2/3/2017  12:16:28 AM 1 1.11 26 z 5.09363 5.094 0.24375 5.09438
2/3/2017  12:17:02 AM 1 1.11 26 z 5.09194 5.09269 0.24375 5.09306

As you can see, the data are separated by sensor address. The address z is the analog-to-digital converter’s address for SDI-12 + Analog adapter. As you can see, my computer outputs 5.09V instead of the nominal 5V on its USB port.

Here is a link to the new logger code. Give it a try and let me know how you like it.

sdi_12_logger_v1_4_1.py

Phi-2 20X4 shield kits

This kit is nearly sold out. Due to Chinese New Year, all re-ordered boards and components are expecting long delays. If Inmojo.com and my paypal sales buttons indicate the kits are sold out, then the kits are indeed sold out. Please be patient and check back in a week or so. Sorry for the inconvenience.

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