Only Keypads I2C Encoder Project

I built Keypad 40 to integrate on a much larger build I was developing for my own use. Keypad 40 in nothing more than a non-intelligent matrix sub-assembly that requires a supporting hardware and software encoder to function as a useful interface. I did prototype Keypad 40 matrix encoder designs into physical PCBs and tested each before finalizing the optimal design to integrate into my personal build. The designs can be found on my Google Site domain onlykeypads.info Keypad 40 worked so well I thought other Hobbyist could benefit from this find. I call it a find because I searched for a keypad to suit my needs and apparently the one or two that would work was over priced for my need. Keypad 40 and encoder designs work well for my use and bench testing proves flawless. Fell free to visit onlykeypads.info and contact me with any thoughts. There is also an alternate contact link on the site. Scrutinize and opinionated thoughts are welcome. I am just a hobbyist who enjoys designing elementary circuits to exercise the mind and learn from others.

The following build will incorporate the steps defining the Keypad 40 and one of the encoder designs Key Easy 4017 Chaser which is the fourth design of five encoder designs total.

As a note: The designs are meant for hobby purposes only and not intended for commercial or consumer products but rather serve as test concepts for future endeavors.

What makes this build unique is the EEPROM on the encoder sum-assembly that allows for custom key characters with a simple swap-out of flashed EEPROMS based on the ASCII table. No need to change the Arduino code for a different character set. The EEPROM can be flashed off-board either with another Arduino or EZP2019 programmer as explained in later steps. In the meantime checkout the EZP2019 on Ebay, you may find it very handy.

Download the ( Instructables Steps pdf ) index file and printout for reference

This build requires two circuit boards and one Arduino. The circuit boards are substituted with prototyping boards for this build. There is a keypad sub-assembly named Keypad 40 and an encoder sub-assembly named Key Easy 4017 Chaser. The Key Easy 4017 Chaser Encoder is the least populated of the five encoder designs. The schematics for both boards will be presented but Step 1 introduces Key Easy 4017 Chaser Encoder sub-assembly with Keypad 40 sub-assembly to follow. Etched boards to populate and where to acquire them will be available soon but the following steps for prototypes are developed for hobbyist to build on their own.

In addition, the following steps will supply the stl and Cura slicer g.code for the Frame so hobbyists with a 3D printer can manufacture their own. I will also supply the file for the paper Overlay. The Frame and Overlay files are for the prototype board footprint and not available to purchase while the manufactured boards will require a different footprint and will be available for purchase once completed.

Keypad 40 material list:

one - (Etched circuit board available soon) this build is based on 9cm x 15cm or larger prototyping board

forty-one - Tactile push buttons (LCSC # C557621)

one - 10k ohm 1/4 watt carbon resistor (can use 1/6 watt to save space)

one - 160 ohm 1/4 watt carbon resistor (can use 1/6 watt to save space)

one - 3mm red LED (keep red to ensure nominal 2vdc 18ma circuit compatibility)

one - 16 pin 2.54mm single row male pin header

Key Easy 4017 Chaser encoder material list:

one - (Etched circuit board available soon) this build is based on 5cm x 10cm or larger prototyping board

one - CD4017BE (DIP-16 Decade Counter)

one - PCF8574P (DIP-16 Expander IC)

five - 2N2222A NPN (Transistors or equivalent switching transistor)

one - AT24C02 (DIP-8 EEPROM)

two - 16 pin DIP IC PCB socket

one - 8 pin DIP IC PCB socket

five - 5k ohm 1/4 watt carbon resistor (can use 1/6 watt to save space)

eleven - 10k ohm 1/4 watt carbon resistor (can use 1/6 watt to save space)

one - 16 pin 2.54mm single row female pin header

one - 8 pin 2.54mm single row male pin header

Additional pre-manufactured items:

One - Arduino of choice

Eight - Dupont wires to connect encoder male pin header to Arduino

22AWG insulated solid patch wire or preference

Soldering tools of preference (Solder: 63/37 blend @ 0.8mm diameter or preference)

The first step is to review the schematic for the Key Easy 4017 Chaser Encoder to gain a visual of design concepts and how pieces fit together. The video will demonstrate the working model that bench tested for an extended time and proves up to this point to be armor plated. The Keypad 40 will be a valuable tool when designing hobby projects that require custom keypad interface. There are many months of design that went from an idea to proven prototypes to manufactured boards. The manufactured boards are undergoing the last revision and will be available once completed.

This Instructables is designed with the hobbyist in mind to take an idea to a working prototype.

The 4017 Chaser Video2.mp4 provides a quick introduction to Keypad 40 operation.

Time to get started!

The first step is to select a prototype board of choice. I chose the 5cm X 10cm board as shown.

Hint: Before populating the board take a fine emery cloth or sandpaper and shine copper traces for easier soldering.

Hint: Review the schematic and trace layout of the prototype board and think ahead where common connections are made, for instance 5vdc and GND to create a power rail or where common junctions between components are made.

A little forward thinking will make assembly easier and the overall finished board will have a professional appearance.

Begin placing components:

16 pin header: Solder the 16 pin female header to the board edge. This header connects the Keypad 40 sub-assembly when finished and to keep the 4017 Chaser components facing front on the finished board when attached to Keypad 40 bend the pins on the female header because the board is single-sided which prevents mounting and soldering of the header on the underside of the board. View the image of the complete assembly for visual reference.

IC sockets: Solder the 8 pin male header, (IC sockets (one 8 pin and two 16 pin)) Notice the component orientation. Mount IC sockets with the notch facing left. Note: IC location from left to right: [AT24C02] [PCF8574P] [CD4017BE]

Transistors: Solder five 2N2222A NPN transistors with the flats facing the 16 pin header. Refer to image for lead identification. Always double check before soldering but placement mistakes do happen. Comes with the territory!

Resistor placement: Due to limited board space 1/6 watt resistors work best. There are two values 10k and 5k so be watchful on placement. Five of the 10k connect from the transistor base to the 16 pin header. The five 5k tie from the PCF8574P pins 4, 5, 6, 7, 9 to +5vdc but notice the yellow patch wires to the transistor collector leads. (Refer to schematic and image)

Three of the 10k resistors connect pins 13,14,15 of the PCF8574P to +5vdc. These serve as (SDA, SCL, Interrupt) pull-up resistors for active low digital states. Basic theory: When a Keypad 40 key is pressed a HIGH +5vdc on the transistor base biases collector to emitter current that references the corresponding PCF8574P I/O port pin (P0 to P7) to GND (LOW) digital state. When the corresponding PCF8574P I/O port pin is driven low it sends an interrupt to the Arduino to read the PCF8574P via I2C bus. The transistors are basic Inverter or NOT gates.

Three of the 10k resistors connect pins 9,11,12 of the CD4017BE to GND. These serve as pull-down resistors for active high digital signals. There are numerous resources on the Internet explaining CD4017BE operation and usage so I will not go into detail as not to muddy the water with over information.

Supplied is a datasheet cut from Texas Instruments PCF8574 Remote 8-Bit I/O Expander for I2C Bus. This is supplied for general information with certain areas highlighted to aid in operational characteristics. Not intended to be technical but to illustrate how micro-controller code has to be considered in advance of interacting with integrated circuits and researching discrete components of choice.

Source: Texas Instruments datasheets

This step is to make the interconnections according to the schematic. This is quite lengthy and can test the patience of a hobbyist but once finished it will be worth the work. Best process is to look at a group of connections, for example points 1 thru 8 on H2 header to CD4017BE and treat them as a group and once done use a highlight pen to mark the schematic as finished. Then choose another group, pins 1 thru 4 on the AT24C02 and repeat the process. The Key Easy 4017 Chaser Encoder is the least populated and that is why it was chosen for this build.

When the Key Easy 4017 Chaser Encoder board is complete a simple biasing check can be performed.

This test will verify that no short circuits exist from the board power supply pins inward when connected to the Arduino.

Required testing equipment

5vdc supply will be required for this test. Type A USB cable with two Dupont wires soldered on the end works for a cheap supply. (Refer to image.) Cutting the female end off and stripping the outer sheath of the USB cable the (red +) and (black -)wires are usually the 5vdc. To test for polarity plug the USB cable into a UL approved 5vdc USB wall adapter and measure with a volt meter. Identify the polarity for future reference.

A simple LED test light will also be needed and one can be assembled using a 150 ohm resistor and a red or green LED rated 2vdc @ 15 to 20ma. (Refer to image).

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Key Easy 4017 Chaser test.

Note: DO NOT insert any ICs in the sockets at this time.

Plug the 5vdc DuPont wires of the power supply positive to (pin 7) and GND to (pin 8) on the eight pin male header.

The first test will check the IC dip socket power pins for proper polarity and 5vdc supply voltage.

With a multi-meter measure for 5vdc across (pin 8 vcc +) and (pin 4 vss -) on the AT24C02. Dip socket

With a multi-meter measure for 5vdc across (pin 16 vcc +) and (pin 8 vss -) on the CD4017BE. Dip socket

With a multi-meter measure for 5vdc across (pin 16 vcc +) and (pin 8 vss -) on PFC8574P. Dip socket

With a multi-meter measure for 5vdc across (pin 15 +) and (pin 16 -) on H2 (sixteen pin female header)

The second test will check the transistors for proper biasing.

This test requires the LED tester.

1- Plug the anode side of the LED tester to pin 15 (+5vdc) of the H2 header

2-Plug the cathode side of the LED tester to pin 4 on the PCF8574P DIP socket.

3-Plug Dupont wire into pin 9 of the 16 pin H2 header. Then touch the other end to +5vdc and the LED will light.

Reference the schematic: By placing +5vdc to pin 9 which is connected to the base of Q1 the transistor is biased ON which allows current flow from collector to emitter referencing the cathode of the LED tester to GND. This is nothing more than a switching transistor circuit.

Perform the following test for Q2, Q3, Q4, Q5

Q2 test (Pin 5 on PCF8574P and pin 10 on H2)

Q3 test (Pin 6 on PCF8574P and pin 11 on H2)

Q4 test (Pin 7 on PCF8574P and pin 12 on H2)

Q5 test (Pin 9 on PCF8574P and pin 13 on H2)

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View the (Transistor video) for a complete test example.

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/W29y3R1BSRA

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If all the tests prove positive then the Key Easy 4017 Chaser Encoder is ready for an bench test.

Integrate hardware to software

At this point a breather is warrant by placing the Key Easy 4017 Chaser through preliminary testing. In actuality this would be part of the design process as sub-assemblies are usually tested individually.

The sub-assembly is complete but the AT24C02 EEPROM programming requires Arduino code before proceeding.

The next step details programming the EEPROM by building a simple breadboard circuit. As mentioned in the Introduction the EZP2019 programmer is more efficient but not every hobbyist will have one so the basic Arduino circuit will be used.

Note: To keep thoughts aligned the instructions for using the EZP2019 will be presented at the end of this build.

Breadboard Circuit for EEPROM Programming

The material is listed below and a schematic image is provided. The build is self explanatory so no detailed assembly is presented but a short video shows the finished breadboard. The schematic uses an Arduino PRO Mini but any Arduino of choice should work fine.

Material:

One breadboard of choice

One Arduino of choice

Arduino USB cable and Arduino IDE software

One AT24C02 EEPROM

Two 10k resistors of choice

Dupont or patch wires of choice. 22awg wire should work on standard breadboards.

Basic Checks before powering the Arduino on:

1- Verify the AT24C02 pinout as related to IC notch

2- Verify AT24C02 SDA (Serial Data) pin 5 connected to Arduino A4

3- Verify AT24C02 SCL (Serial Clock) pin 6 connected to Arduino A5

4- Verify the two 10k pullup resistors for placement and are connected to +5vc

5- Verify +5 volt and GND power rail connections for polarity.

6- AT24C02 requires 5vdc to operate properly.

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View the (video) for Arduino AT24C02 EEPROM Breadboard Programmer

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/tGOj95p9NNE

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---------With Step 7 (Part 2) complete----------

Step 8 (Part 3) explains the downloading of Arduino code required to program the EEPROM

1st ----- In Windows build the file structure in your Documents folder

Before downloading the Arduino code a file structure is required for the program file to execute properly. For the hobbyist not familiar with Arduino file structure it can be confusing at first so an example is provided with a short video below.

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View the (video) for Arduino "File Structure"

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/ZS3yaRqq0pY

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2nd ----- Download Arduino files into your file folder as explained in the video

The Keypad 40 Arduino code files are available below for download: There are two files: Download both files.

keypad_burn_eeprom_write.ino and eeprom_write_func.ino ----- (Refer to video and images)

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3rd ----- Download Arduino IDE software from Internet

The Arduino IDE software is required to launch the files you just downloaded

I prefer the Arduino IDE launcher on a Windows computer but there is an online version for Chromebook.

For first time users I suggest the Windows version

Windows download link: https://www.arduino.cc/en/software

Chromebook: https://www.aboutchromebooks.com/news/how-to-code-an-arduino-with-a-chromebook/

The Chromebook link explains how to program an Arduino with a Chromebook using a Chrome extension.

The method chosen will require research and there are many YouTube and articles available for first time users.

Before programming the EEPROM an understanding of (Keypad 40) key character layout is required.

The following explains the (Key Easy 4017 Chaser) external EEPROM addressing. 

Using the ASCII table and the Keypad 40 address ID table the EEPROM can be programmed for various key characters. (Each Keypad 40 tactile button has a permanent EEPROM address number as shown)

These address numbers are fixed in the Arduino code and cannot be altered

The Keypad 40 address ID table shows the Key Character and programming parameters for the EEPROM basic character set. The user can modify each key with ASCII characters of choice but for now the characters shown are used.

In order to understand this method of addressing I supplied a video with a detailed description and also a written description below but suggest watching the video first before reading the description below.

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View the (video) for EEPROM addressing explanation.

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/qZS4z2LdqbE

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Reference: (Keypad 40 address ID) table

1-The "Keypad Key Character" represents the keypad eight columns by five row layout. Each key can be character customized as required.

5-On the manufactured (Keypad 40 sub-assembly) the "PCB switch ID" silk screen represents the unique EEPROM cell address of each individual key.

2-The "EEPROM Cell Address" is the unique EEPROM address of each individual key. This address is fixed in the Arduino program.

     DO NOT use any other Cell Address locations or the code will not function as intended.

3-The "ASCII code Key character DECIMAL value" represents the value in decimal for each character in the ASCII table.

    The user defined decimal value will be loaded into the EEPROM cell address to represent the individual key character as required when using an Arduino via the Serial Monitor to program the EEPROM.

Programming from the Serial Monitor will be explained in detail in the Step 9 video.

Note: There are many options available to program an EEPROM and any other will yield the same results being the EEPROM Cell Address is maintained.

Print copy available for:

The "pdf" file for (Keypad 40 address ID)

The "pdf" file for (ASCII Table)

Notice on the Serial Monitor example that for EEPROM location '10 ' the ASCII decimal '97' is entered for the Key Character 'a' lower case. If Keypad 40 requires other characters on the ASCII table the corresponding ASCII decimal value for the character is entered for the particular key being programmed. Example: decimal '61' for '=' can be entered.

As shown on the Key Matrix image each tactile key has an EEPROM cell address that is fixed in the Arduino code and with this address being fixed only the character decimal value requires entry to change the key character.

The following videos describe in detail the programming of the EEPROM before installing it on the Key Easy 4017 Chaser Encoder board.

First video is a review of previous videos tying it all together from breadboard to programming the EEPROM.

Second video breaks down the EEPROM write code line by line.

First Video:

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EEPROM programming explanation. (Breadboard to Serial Monitor programming)

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/hMt-9fP19TA

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Second Video:

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EEPROM write code on Arduino IDE. (Breaks down code line by line)

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/bYr4x-fWK9A

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Now that the EEPROM is programmed the ICs will be installed on the Key Easy 4017 Chaser board. Use the image as a guide on the order of install. The 8 pin male header will be connected to the Arduino of choice according to the image schematic. The test LED built earlier will be required along with a normally open push button with 22awg wires connected to the two terminals.

Before any testing can begin the Arduino IDE code will have to be downloaded. Basically the same procedure is followed from earlier with an additional folder in the Documents/Arduino Projects folder. The folder must be named (Keypad_4017_chaser_2.2) in order for the download to execute in the Arduino IDE. A flow chart image is provided as a guide on creating the folder and files to download. Also review the video for reference.

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View the (video) for downloading code on Arduino IDE.

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/8VmC7SUOfKI

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The three files for download are available below. The Keypad_4017_chaser_2.2A.ino is the main code and the other two: Keypad_PCF8574_Test.ino and keypad_eeprom_read.ino are function files.

This code will be executed in the finished (Keypad 40) build even though it is being used for the bench test.

It is specifically written for the (Keypad40) to communicate with the (Key Easy 4017 Chaser Encoder).

When the bench test is complete the Keypad 40 will be built in the following steps and connected to the Key Easy 4017 Chaser via the Arduino running this code. That will complete the assembly to communicate with other I2C devices such as another Arduino, LCD display, ETC.

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View the (video) for testing the Key Easy 4017 Chaser with a push button.

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/-134H09fE0U

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It is time to construct the Keypad 40 keypad. The material list is listed above but for convenience the same list is added in this step. There are some screen shots showing the prototype board used and the schematic layout of the components with inter connections. Also the general layout of keys, the PLA 3D frame and paper template provided later with download files to print. The last image shows the finished assembly to gain an idea on how it should look.

This build is time consuming but well worth it when operational. It was not without small issues when I built it. Check for cold solder joints and solder bridges. When complete scrub the solder areas with Simple Green or 90% alcohol to remove solder debris between tight joints. I had a couple of joints with debris to act as high resistance joints that caused erratic function. Comes with the territory and can be frustrating to solve but serves as troubleshooting experience.

View the video below of the completed build.

Keypad 40 material list:

one - (Etched circuit board available soon) this build is based on 9cm x 15cm or larger prototyping board

forty-one - Tactile push buttons (LCSC # C557621)

one - 10k ohm 1/4 watt carbon resistor (can use 1/6 watt to save space)

one - 160 ohm 1/4 watt carbon resistor (can use 1/6 watt to save space)

one - 3mm red LED (keep red to ensure nominal 2vdc 18ma circuit compatibility)

one - 16 pin 2.54mm single row male pin header

22AWG insulated solid patch wire or preference

Soldering tools of preference (Solder: 63/37 blend @ 0.8mm diameter or preference)

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View the (video) of the completed build.

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/gpB4amzxsKk

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3D Frame stl file developed in Tinkercad

Note: The frame is hollow on the underside.

Download stl file from Google Drive.

Paste in your URL for download:

https://drive.google.com/file/d/1GgZvSYrqrrPuE3KR84BeerB-thcZr255/view?usp=sharing

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3D Frame g.code file developed in CURA slicer. If your printer accepts CURA g.code you are all set, if not use the stl file to create another slicer file for your printer in proper g.code format.

Note: The frame is hollow on the underside so flip with the hollow side up if developing new g.code from stl file.

Download g.code file from Google Drive.

Paste in your URL for download:

https://drive.google.com/file/d/1GegboFxpGqFCFwM328c6fk-6mSLBBiiL/view?usp=sharing

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Blank Paper Template

Download for Paper Template from Google Drive. PNG file for use in Windows Paint for modification and printout.

Paste in your URL for download:

https://drive.google.com/file/d/1GX6434znfRTGgBsmj0068XjGhcpVfHmr/view?usp=sharing

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Standard Paper Template with Common Characters

Download for Paper Template from Google Drive. PNG file for use in Windows Paint for modification and printout.

Paste in your URL for download:

https://drive.google.com/file/d/1GXGVtZFgthRCfwnj8zOAFAoTtuvYxTvb/view?usp=sharing

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Use Elmer's School Glue to attach paper template to PLA frame. This allows easy removal for replacement templates.

Hint: Use Label printer with adhesive labels for printout.

The EZP2019 programming is based on the HEX value of the character. Remember the Arduino EEPROM programming used the Decimal value of the character from the ASCII table while the EZP2019 requires the HEX value of the character.

The set has a supplied CD with the driver software. Ebay has the EZP2019 from multiple suppliers and there are many YouTube videos on applications pertaining to programming Computer BIOS chips so I supplied a video for the basic needs of programming the AT24C02 EEPROM for simplicity.

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View the (video) of the EZP2019 programmer

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/h31r7csoTmo

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This gives some closure to the build by demonstrating an idea to prototyping to manufactured PCBs. The video below includes not only the manufactured board for Key Easy 4017 Chaser but an added design Key Easy Two Wire that is worth while watching.

I want to thank Instructables for allowing my presentation to others along with the necessary information to built your custom Key Easy 4017 Chaser Encoder and Key Pad 40 keypad.

There is further information on onlykeypads.info for interested hobbyists to explore.

Take time to view the video for greater insight on the builds.

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View the (video) on Key Easy 4017 Chaser and Key Easy Two Wire keypad encoders.

Copy the YouTube URL and paste into your URL address bar for viewing

https://youtu.be/SX19nVpwH_E

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End of Build, Thanks for taking interest. Bob K.