Serial 4 X 4 Keypad Schematic

Keypads are used in all types of devices, including cell phones, fax machines, microwaves, ovens, door locks, etc. Find this and other hardware projects on Hackster.io.

Figuring out the matrix wiring of the 4x4 keypad is dead simple with an ohm meter. Attach the meter leads to selected pairs of the conductors in the connection cable.

Then press the buttons one at a time to see which switch closes the connection between the selected conductors. If you write down the connection numbers as 1 to 8 and then make a table of the selected pairs in sequence and which switch closes each pair.

Some pairs will not cause any closures to be registered. When this happens you will know that the selected pair of connection wires are either both row wires in the switch matrix or column wires. I've search over the net but i can't see its pin configuration.

I assume I'm seeing an 8 wire tail. Just maybe 7. The keypad is likely to have the connections brought out as 4 rows and 4 columns. If there is a 9th wire it may be a shield. Use an Ohm meter set to say something like 100k (or 199.9k or whatever) range. This allows you to not miss very high resistance contacts. A 20k range MAY be OK but 200k is safer.

Make contact with conductive end of tail with meter probes. Try putting 2 probes on the same tail and ensure you can easily see the meter respond - most tails will be insulated until near the end and some may be oxidised on the conductive surfaces and need a CAREFUL rub with the meter probe tip to make contact. Tails may be made by depositing conductive ink so will usually not be super strong so use reasonable care when making contact. They are usually not super delicate - just be sensible. IF you have a connector for the keyboard, use it. I'll assume 8 conductors numbered 1 to 8 below.

Adjust as needed. Having an assistant is not essential but helps. Hold down one key and place one probe on contact 1 (1st wire) and go along all other wires 2-8 with probe to see if a contact can be found.

If not, place one probe on 2nd wire (contact 2) and go along 3-8. Then 3 + 4-8 4 + 5-8 5 + 6-8 6 + 7-8 7 + 8 If you do not get a contact closure on ANY of the above then you are not making proper contact (most likely) or the keyboard is dead (less likely). Record the result and try another key. After a few tries a pattern will appear. Probably 4 x row and 4 x column as above. An alternative method is to choose two contacts for meter probes and press keys in turn until a closure occurs eg contacts on 2 + 5 MAY respond to key 4.

(2nd row, 5-4 = 1 = 1st column) but may not. This method MUST work if done properly if the matrix has only switches. SOME keyboards have internal diodes but this is extremely unlikely for your keyboard.

For keyboards with diodes, meter polarity matters. Kayboards that look very like yours can be found at: Here - see below - same arrangement. Manufacturer: Parallax Product Code: Dev-4x4Key-01 for $ less.

Matrix Keypad Basic Connection The rows R0 to R3 are connected to Input lines of Microcontroller. The i/o pins where they are connected are made Input. This is done by setting the proper in AVR and TRIS Register in PIC. The column C0 to C3 are also connected to MCUs i/o line. These are kept at High Impedance State (AKA input), in high z state (z= impedance) state these pins are neither HIGH or LOW they are in TRISTATE. And in their PORT value we set them all as low, so as soon as we change their DDR bit to 1 they become output with value LOW.

One by One we make each Column LOW (from high Z state) and read state of R0 to R3. Column 1 Selected How to Do it All with AVRs Each i/o port in AVR has three related registers PORTx, DDRx and PINx.

For example port A has • PORTA Port Driver – when any bit is set to 1 it appears as HIGH i.e. But this is the case only if that bit is OUTPUT. If it is input, setting any bit to 1 enables the internal pullup on that bit. • DDRA DATA DIRECTION REGISTER – Make any pin on than port as IN or OUT. When bit is 1 it represents Output. When bit is 0 it represents Input. Input state is also called tristate or high Z state.

• PINA – Read it to get the level (HIGH or LOW) at the actual i/o pin. It is read when the pin is made input. So now you know • How to make any i/o line Input(high Z) or Output. • How to enable internal pullup register on input lines. • How to read value that is present on input lines. Please see the following tutorial for more clarification.

• Why we make other Columns High Impedance while one column is made LOW? Lets say we selected column number C0, so we make it LOW(i.e. GND or logic 0), in the same time we make all other columns high impedance (i.e.

If we don’t make other lines high impedance (tristate or Input) they are in output mode. And in output mode they must be either LOW(GND or logic 0) or HIGH (5v or logic 1). We can’t make other lines LOW as we can select only one line at a time and C0 is already low as per assumption. So the only other possible state is all other columns are HIGH. This is shown in figure below.

Red colour on column indicate high state while green is for low state. ATmega32 + LCD + Keypad Interface. We have built the above circuit on a, but it does not has inbuilt LCD Module connector so you need to solder it yourself at the free area (and also do the wiring). Compile the above program using AVR Studio (compiler is avr-gcc). And finally burn the program using any to the ATmega32. The fuse bits must be set as following to enable external crystal as clock source. • High Fuse = C9 (hex value) • Low fuse =FF (hex value) After burning the HEX file to MCU, finally you are ready to power up the setup.

When powered on, the LCD Screen Should show you the keycode of the key pressed on the keypad. This complete our test. Troubleshooting • NO Display on LCD • Make sure AVR Studio Project is set up for clock frequency of 16MHz (16000000Hz) • Adjust the Contrast Adj Pot.

• Press reset few times. • Power On/Off few times. • Connect the LCD only as shown on schematic above. • No response to key press.

• Check that keypad is connected on PORTA only. • If you want to attach keypad on different port, change the line 80 on source code (keypad.c) • #define KEYPAD A //KEYPAD IS ATTACHED ON PORTA • Compiler Errors • Many people these days has jumped to embedded programming without a solid concept of computer science and programming. They don’t know the basics of compiler and lack experience. To learn basic of compilers and their working PC/MAC/Linux( I mean a desktop or laptop) are great platform. But embedded system is not good for learning about compilers and programming basics.

It is for those who already have these skills and just want to apply it. • Make sure all files belonging to the LCD Library are 'added' to the 'Project'.

• avr-gcc is installed. (The Windows Binary Distribution is called ) • The AVR Studio project Type is AVR GCC. • • • General Tips for newbies • Use ready made and. • Try to follow the from the very beginning. (Remember the list spans four pages, page 1 is most recent addition thus most advance) Video For 4×3 Keypad Interfacing. User Videos By Brendin I really appreciate Brendin’s approach on getting his problem solved and successfully porting the demo to ATmega48.

What I recommend the users is to get your basics strong. You need full understanding of C language concept and the full details of the device you are programming, this will save you lots of time. So please go and read the good book on C and the datasheet of AVRs before you dive in! – Avinash Downloads • • • Help Us! Andy Timmons Resolution Tab Book Pdf. We try to publish beginner friendly tutorials for latest subjects in embedded system as fast as we can.

If you like these tutorials and they have helped you solve problems, please help us in return. You can donate any amount as you like securely using a Credit or Debit Card or Paypal. We would be very thankful for your kind help. By Avinash Gupta, Follow on. Great tutorial.

Could this be adapted for my atmega48 mcu? I was able to get the LCD tutorial to compile for the 48 but this one won’t build.

I got it working on the atmega48. I needed to also set the reset pin disable to set PC6 as I/O (this unfortunately means I can no longer program with the ISP programmer).

The code works for every button except 2 and 3 (using a 4×3 keypad 2 and 3 are equivalent to 2nd and 3rd button on the top row in this tutorial). When I hold down the 2 button the LCD flashes between 0 and 1 very fast. When I hold down 3 button the same thing happens but flashes between 0 and 2. All the other buttons work properly I am not using an external clock. Fuse settings are Low=E2 High=5F and Extended=FF What would cause this? Thanks, Brendin •.

I changed some things around and got it working. I put the lcd data on port C and the keypad on port B. Now I don’t have to worry about setting port c6 as an input and disabling reset. All of the keys output as expected. Here is a youtube link. Changes I made lcd.h /************************************************ LCD CONNECTIONS *************************************************/ #define LCD_DATA C//Port PB0 TO PB3 are connected to D4-D7 #define LCD_E C //Enable/strobe signal #define LCD_E_POSPC4// PB4 Position of enable in above port Keypad.c #define KEYPAD B//KEYPAD IS ATTACHED ON PORTA •.

@Avinash I understand ur point of view. But if a person has already got a toy car, all opened up then why hesitate in experimenting. If u have time can u atleast tell how can i connect an AtmegaXX to the RF toy car circuit Correct me if i am wrong anywhere. Another question is how can i increase aerial data transfer range if i bought a RF module, for, currently i noe its limited to a modest span of some feet.

Cuz elec.mag waves can propagate long distances. Is it achieved with the aid of repeaters (Power Boosting ).

And if i dont have repeaters(non commercial experimentation) then how can i increase range of RF module by increasing its Power i/p. Hi Avinash, As Brendin said that to use PC6 as input we have to disable RESET. How can we program AVR in such cases? Whenever, I use PC6 as output, on pressing the RESET switch, how does RESET gets activated,or, what happens internally??? Does it generate some kind of interrpt??? Somedays ago in a wireless robo-boat championship I saw that none of the boats were working. All the boats had RF modules attached all of the same frequency, but DIFFERENT ADDRESS BITS set in the Rx and Tx.

Can you explain? Is it because all of them were trying to work at the same frequency? If yes, Why are address bits provided in Rx and Tx modules using a DIP switch. Thank You in advance •.

Hi Avinash, Thank you for this great tutorial. I need your help. I have built the the 4×3 Matrix Keypad Interface – AVR Tutorial using Atmega162.

I did not change anything only the microcontroller. I kept the c code as it is. I built it exactly as yours but i am not getting the digit in the LCD as yours. I am getting random keys. My question is the keypad has got 7 pins and could you please help me to find out which one is pin1 to pin7 and which pin is columns and rows. I have buzzed the keypad and I came out with this configuration: ROW1->PIN2->PA0 ROW2->PIN7->PA1 ROW3->PIN6->PA3 ROW4->PIN4->PA4 COL1->PIN3->PA6 COL2->PIN1->PA5 COL3->PIN5->PA4 Another question is from other website I have found out that they connect the column with 150 Ohms resistor and the row with 10K to ground, why?

Hello everyone, I have an excercise that conciste to program a 3×4 button keypad. However, each button must have: >Display the number of the button on the LCD >Calman V5 Keygen Software. Save a value of a defined position. The first idea that I try to apply is: The implementation of a short and long button action. For this I read the functions of Peter Dannegger that not seem the way to the case of a keypad. The equipment I use is the suivatn: Atmelstudio 7 April STK500 ATmega16 (L) ISP RS 232 3×4 Keypad Is there anyone who can offer me an alternative idea, if someone can give me a code that made the action to the case of a keypad.