Temporary connections?

March 22, 2017 Leave a comment

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.

Filed under Arduino, Soldering

SDi-12 + GPS USB adapter test

March 19, 2017 10 Comments

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:

Commands:

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:

zM!
z0012
z
zD0!
z-09456.1234+4578.9012
zM1!
z0011
z
zD0!
z+190317
zM2!
z0011
z
zD0!
z+065402

Concurrent measurement:

zC!
z00102
zD0!
z-09456.1234+4578.9012
zC1!
z00101
zD0!
z+190317
zC2!
z00101
zD0!
z+065713

Filed under data logging, Gadgets, SDI-12 Tagged with GPS, SDI-12

SDI-12 + GPS module

March 18, 2017 1 Comment

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

USB connection
SDI-12 translator with 4 SDI-12 connections (on a single SDI-12 bus)
Header for a GPS module
External power connection for sensors that need more than 5V from USB
External power/5V USB selection jumper
You can also use other serial devices or sensors such as Maxbotix serial sonic ranger, with some modification to the firmware
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.

Filed under Announcements, data logging, Gadgets, SDI-12 Tagged with data logger, SDI-12, SDI-12 adapter

Phi-panel circuit board update

March 17, 2017 Leave a comment

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:

Filed under Announcements, Arduino, Gadgets

I2C LCDs

March 16, 2017 1 Comment

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/