Programmer Dvorak Terminal Keyboard

This project builds a compact Dvorak keyboard paired with an Arduino Uno and 16x2 LCD display, designed to teach command-line skills through interactive lessons. The keyboard uses a 6x6 button matrix wired to the Arduino's digital pins, with the LCD showing lesson prompts and simulated terminal output as users practice typing common Linux commands.

The guide includes a complete wiring diagram showing how to connect the matrix buttons, LCD display with contrast control via potentiometer, and all necessary resistors. Assembly steps walk through organizing the button contacts into rows and columns, connecting the display power and data lines, and verifying the circuit before loading the firmware that maps Dvorak key positions and manages the 12-lesson curriculum.

Wiring diagram

Loading diagram…

Gather all the parts

Qty	Component
1	Steren ARD-380 LCD 16x2 5 V HD44780 parallel display. Standard numbered 16-pin header; verify printed labels before power.
1	10kΩ Potentiometer Steren 101-10K, 10 kΩ 10 kΩ linear (B10K) rotary potentiometer in the common 16 mm panel style: metal can, M7 threaded bushing for mounting through a panel, a 6 mm knurled split shaft for push-on knobs, and three PCB pins in a row 5 mm apart. Connect the outer pins across 3.3 V or 5 V and ground; the middle wiper pin then gives an adjustable voltage for an ADC input over about 300° of rotation.
1	Resistor Steren R220 1/2, 220 Ω 1/2 W Through-hole resistor (current-limiting in series with an LED)
1	Button 01: ; Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 02: , Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 03: . Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 04: p Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 05: y Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 06: f Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 07: g Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 08: c Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 09: r Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 10: l Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 11: a Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 12: o Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 13: e Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 14: u Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 15: i Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 16: d Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 17: h Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 18: t Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 19: n Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 20: s Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 21: ' Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 22: q Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 23: j Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 24: k Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 25: x Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 26: b Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 27: m Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 28: w Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 29: v Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 30: z Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 31: SPACE Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 32: BACK Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 33: ENTER Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 34: SHIFT Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 35: FN Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.
1	Button 36: LESSON Normally open momentary switch. A and B are the two separate switch contacts. On a four-leg tactile switch each contact has two internally joined legs; use one leg from each contact. Existing buttons, or Steren normally-open miniature push switch.

Assemble it in 10 steps

1. Gather the remaining parts

Use 36 normally-open momentary buttons total (reuse yours). For extra buttons Steren offers the miniature normally-open red push switch: https://www.steren.com.mx/switch-miniatura-de-push-normalmente-abierto-de-127-vca-color-rojo.html . Buy the Steren ARD-380 parallel LCD, a 101-10K 10 kΩ potentiometer and R220 1/2 220 Ω resistor. You also need a USB cable, suitable mounting board, and wire. The display has no adapter; solder wires directly or fit a header.

Do not connect any part to household electricity. Use USB 5 V only. Unplug USB before wiring or soldering.

2. Connect display power and contrast

Check the LCD printed pin labels and numbering, not its viewing orientation. Pin 1 VSS goes to GND, pin 2 VDD to 5V. Connect the potentiometer outer legs to 5V and GND; its middle leg goes to LCD pin 3 VO (contrast). LCD pin 5 RW goes to GND (write-only).

Reversed power can destroy the display.

3. Connect the screen data wires

LCD pin 4 RS → A0 (command or text), pin 6 E → A1 (enable), pin 11 D4 → A2, pin 12 D5 → A3, pin 13 D6 → A4, pin 14 D7 → A5 (four data lines). Leave LCD pins 7–10 unconnected. The analog pins are used as ordinary digital pins here.

4. Connect the backlight safely

5V → 220 Ω resistor → LCD pin 15 A (backlight positive). LCD pin 16 K goes to GND. The resistor can face either direction.

5. Identify the button contacts

Each button needs two electrically separate contacts, A and B. On a four-leg tactile button, two legs are already joined on each contact. Use one leg from each separate contact; leave the duplicate legs unused. If uncertain, verify the pairs with continuity testing before wiring. On a two-terminal Steren switch use one terminal for A and one for B. Buttons have no polarity.

A latching on/off switch is not suitable; the button must spring back to open when released.

6. Wire the six scan rows

For buttons 01–06 join contact A to D2; 07–12 to D3; 13–18 to D4; 19–24 to D5; 25–30 to D6; 31–36 to D7. These are electrical groups, independent of the physical keyboard rows. Do not connect button contacts directly to power or GND.

7. Wire the six scan columns

Contact B: buttons 01,07,13,19,25,31 → D8; 02,08,14,20,26,32 → D9; 03,09,15,21,27,33 → D10; 04,10,16,22,28,34 → D11; 05,11,17,23,29,35 → D12; 06,12,18,24,30,36 → D13. Leave D0 and D1 free for USB programming. Internal pull-up resistors are used.

8. Arrange and label the keypad

Arrange three physical rows of ten: 01–10 = ; , . p y f g c r l; 11–20 = a o e u i d h t n s; 21–30 = ' q j k x b m w v z. A fourth row holds 31 SPACE, 32 BACK, 33 ENTER, 34 SHIFT, 35 FN, 36 LESSON. This is a compact Programmer Dvorak adaptation, not a full-size keyboard. SHIFT and FN are pressed and released before the character, never held together. LESSON restarts the course.

9. Check the assembled circuit

Inspect solder joints for shorts. Power by USB and slowly turn the contrast knob until letters appear. Top line shows the exact task; bottom line shows your typing. Press ENTER to check. On success, read the simulated result and press ENTER again for the next lesson. After a mistake, use BACK to edit and retry. Type one button at a time.

There are 12 guided lessons. This validates the displayed command, not arbitrary Linux syntax. No real files are created; lesson state resets when power is removed.
The input limit is 48 characters. The last 15 typed characters remain visible. S means Shift is ready, F means Fn, and N means Fn plus Shift.

10. Keep the symbol labels with your keypad

# Compact Programmer Dvorak key labels Tap and release Shift or Fn before the character. Tap Fn, then Shift, then a key for digits. Never hold multiple buttons. 01: ; Fn: & Fn+Shift: 7 02: , Fn: [ Fn+Shift: 5 03: . Fn: { Fn+Shift: 3 04: p Fn: } Fn+Shift: 1 05: y Fn: ( Fn+Shift: 9 06: f Fn: = Fn+Shift: 0 07: g Fn: * Fn+Shift: 2 08: c Fn: ) Fn+Shift: 4 09: r Fn: + Fn+Shift: 6 10: l Fn: ] Fn+Shift: 8 11: a Fn: ! 12: o Fn: # 13: e Fn: $ 14: u Fn: @ 15: i Fn: / 16: d Fn: - 17: h Fn: \ 18: t Fn: ` 19: n Fn: ~ 20: s Fn: : 21: ' Fn: % 22: q Fn: ^ 23: j Fn: | 24: k Fn: _ 25: x Fn: ? 26: b Fn: < 27: m Fn: > 28: w Fn: " 29: v Fn: . 30: z Fn: , 31 Space; 32 Backspace; 33 Enter; 34 Shift; 35 Fn; 36 Restart lessons. Physical rows: 01–10, 11–20, 21–30, then six controls. Shift capitalizes letters and changes ; , . and apostrophe to : < > and double quote. This is a compact adaptation, not a full-size layout. Type the exact task on the top line and press Enter. On success, Enter advances. Tasks: pwd, ls, mkdir practice, cd practice, touch notes.txt, ls, cat notes.txt, echo hello, rm notes.txt, cd .., rmdir practice, clear. Only these guided tasks are validated. Outputs are illustrative: this is not Linux and has no filesystem. Progress resets at power-off.

Review all connections

1. Connections between "lcd" and "Arduino"

Function	lcd	Arduino
`ground`	VSS	GND
`power`	VDD	5V
`analog`	VO → 10kΩ Potentiometer WIPER	EXT
`ground`	RW	GND
`digital`	RS	GPIO 14
`digital`	E	GPIO 15
`digital`	D4	GPIO 16
`digital`	D5	GPIO 17
`digital`	D6	GPIO 18
`digital`	D7	GPIO 19
`ground`	K	GND

2. Connections between "contrast" and "Arduino"

Function	contrast	Arduino
`ground`	GND	GND
`power`	VCC	5V

3. Connections between "backlight_r" and "Arduino"

Function	backlight_r	Arduino
`power`	P1	5V
`digital`	P2 → Steren ARD-380 LCD 16x2 A	EXT

4. Connections between "key01" and "Arduino"

Function	key01	Arduino
`digital`	A	GPIO 2
`digital`	B	GPIO 8

5. Connections between "key02" and "Arduino"

Function	key02	Arduino
`digital`	A → Button 01: ; A	EXT
`digital`	B	GPIO 9

6. Connections between "key03" and "Arduino"

Function	key03	Arduino
`digital`	A → Button 01: ; A	EXT
`digital`	B	GPIO 10

7. Connections between "key04" and "Arduino"

Function	key04	Arduino
`digital`	A → Button 01: ; A	EXT
`digital`	B	GPIO 11

8. Connections between "key05" and "Arduino"

Function	key05	Arduino
`digital`	A → Button 01: ; A	EXT
`digital`	B	GPIO 12

9. Connections between "key06" and "Arduino"

Function	key06	Arduino
`digital`	A → Button 01: ; A	EXT
`digital`	B	GPIO 13

10. Connections between "key07" and "Arduino"

Function	key07	Arduino
`digital`	A	GPIO 3
`digital`	B → Button 01: ; B	EXT

11. Connections between "key08" and "Arduino"

Function	key08	Arduino
`digital`	A → Button 07: g A	EXT
`digital`	B → Button 02: , B	EXT

12. Connections between "key09" and "Arduino"

Function	key09	Arduino
`digital`	A → Button 07: g A	EXT
`digital`	B → Button 03: . B	EXT

13. Connections between "key10" and "Arduino"

Function	key10	Arduino
`digital`	A → Button 07: g A	EXT
`digital`	B → Button 04: p B	EXT

14. Connections between "key11" and "Arduino"

Function	key11	Arduino
`digital`	A → Button 07: g A	EXT
`digital`	B → Button 05: y B	EXT

15. Connections between "key12" and "Arduino"

Function	key12	Arduino
`digital`	A → Button 07: g A	EXT
`digital`	B → Button 06: f B	EXT

16. Connections between "key13" and "Arduino"

Function	key13	Arduino
`digital`	A	GPIO 4
`digital`	B → Button 01: ; B	EXT

17. Connections between "key14" and "Arduino"

Function	key14	Arduino
`digital`	A → Button 13: e A	EXT
`digital`	B → Button 02: , B	EXT

18. Connections between "key15" and "Arduino"

Function	key15	Arduino
`digital`	A → Button 13: e A	EXT
`digital`	B → Button 03: . B	EXT

19. Connections between "key16" and "Arduino"

Function	key16	Arduino
`digital`	A → Button 13: e A	EXT
`digital`	B → Button 04: p B	EXT

20. Connections between "key17" and "Arduino"

Function	key17	Arduino
`digital`	A → Button 13: e A	EXT
`digital`	B → Button 05: y B	EXT

21. Connections between "key18" and "Arduino"

Function	key18	Arduino
`digital`	A → Button 13: e A	EXT
`digital`	B → Button 06: f B	EXT

22. Connections between "key19" and "Arduino"

Function	key19	Arduino
`digital`	A	GPIO 5
`digital`	B → Button 01: ; B	EXT

23. Connections between "key20" and "Arduino"

Function	key20	Arduino
`digital`	A → Button 19: n A	EXT
`digital`	B → Button 02: , B	EXT

24. Connections between "key21" and "Arduino"

Function	key21	Arduino
`digital`	A → Button 19: n A	EXT
`digital`	B → Button 03: . B	EXT

25. Connections between "key22" and "Arduino"

Function	key22	Arduino
`digital`	A → Button 19: n A	EXT
`digital`	B → Button 04: p B	EXT

26. Connections between "key23" and "Arduino"

Function	key23	Arduino
`digital`	A → Button 19: n A	EXT
`digital`	B → Button 05: y B	EXT

27. Connections between "key24" and "Arduino"

Function	key24	Arduino
`digital`	A → Button 19: n A	EXT
`digital`	B → Button 06: f B	EXT

28. Connections between "key25" and "Arduino"

Function	key25	Arduino
`digital`	A	GPIO 6
`digital`	B → Button 01: ; B	EXT

29. Connections between "key26" and "Arduino"

Function	key26	Arduino
`digital`	A → Button 25: x A	EXT
`digital`	B → Button 02: , B	EXT

30. Connections between "key27" and "Arduino"

Function	key27	Arduino
`digital`	A → Button 25: x A	EXT
`digital`	B → Button 03: . B	EXT

31. Connections between "key28" and "Arduino"

Function	key28	Arduino
`digital`	A → Button 25: x A	EXT
`digital`	B → Button 04: p B	EXT

32. Connections between "key29" and "Arduino"

Function	key29	Arduino
`digital`	A → Button 25: x A	EXT
`digital`	B → Button 05: y B	EXT

33. Connections between "key30" and "Arduino"

Function	key30	Arduino
`digital`	A → Button 25: x A	EXT
`digital`	B → Button 06: f B	EXT

34. Connections between "key31" and "Arduino"

Function	key31	Arduino
`digital`	A	GPIO 7
`digital`	B → Button 01: ; B	EXT

35. Connections between "key32" and "Arduino"

Function	key32	Arduino
`digital`	A → Button 31: SPACE A	EXT
`digital`	B → Button 02: , B	EXT

36. Connections between "key33" and "Arduino"

Function	key33	Arduino
`digital`	A → Button 31: SPACE A	EXT
`digital`	B → Button 03: . B	EXT

37. Connections between "key34" and "Arduino"

Function	key34	Arduino
`digital`	A → Button 31: SPACE A	EXT
`digital`	B → Button 04: p B	EXT

38. Connections between "key35" and "Arduino"

Function	key35	Arduino
`digital`	A → Button 31: SPACE A	EXT
`digital`	B → Button 05: y B	EXT

39. Connections between "key36" and "Arduino"

Function	key36	Arduino
`digital`	A → Button 31: SPACE A	EXT
`digital`	B → Button 06: f B	EXT

Deploy the firmware

main.cppOpen in Schematik

#include <Arduino.h>
#include <LiquidCrystal.h>
#include <avr/pgmspace.h>
#include <ctype.h>
LiquidCrystal lcd(A0,A1,A2,A3,A4,A5);
// Wiring verified: shared row contacts D2-D7, shared columns D8-D13.
// LCD RS/E/D4/D5/D6/D7 use A0/A1/A2/A3/A4/A5.
const uint8_t rows[6]={2,3,4,5,6,7};
const uint8_t cols[6]={8,9,10,11,12,13};
const char normal[] PROGMEM=";,.pyfgcrlaoeuidhtns'qjkxbmwvz";
const char symbols[] PROGMEM="&[{}(=*)+]!#$@/-\\`~:%^|_?<>\".,";
const char numbers[] PROGMEM="7531902468";
const char l0[] PROGMEM="pwd";
const char l1[] PROGMEM="ls";
const char l2[] PROGMEM="mkdir practice";
const char l3[] PROGMEM="cd practice";
const char l4[] PROGMEM="touch notes.txt";
const char l5[] PROGMEM="ls";
const char l6[] PROGMEM="cat notes.txt";
const char l7[] PROGMEM="echo hello";
const char l8[] PROGMEM="rm notes.txt";
const char l9[] PROGMEM="cd ..";
const char l10[] PROGMEM="rmdir practice";
const char l11[] PROGMEM="clear";
const char* const lessons[] PROGMEM={l0,l1,l2,l3,l4,l5,l6,l7,l8,l9,l10,l11};
const char o0[] PROGMEM="/home/student";
const char o1[] PROGMEM="(empty folder)";
const char o2[] PROGMEM="Directory made";
const char o3[] PROGMEM="In practice/";
const char o4[] PROGMEM="File created";
const char o5[] PROGMEM="notes.txt";
const char o6[] PROGMEM="(empty file)";
const char o7[] PROGMEM="hello";
const char o8[] PROGMEM="File removed";
const char o9[] PROGMEM="/home/student";
const char o10[] PROGMEM="Folder removed";
const char o11[] PROGMEM="Course complete!";
const char* const outputs[] PROGMEM={o0,o1,o2,o3,o4,o5,o6,o7,o8,o9,o10,o11};
char input[49]={0}, previous[2][17]={{0}};
uint8_t used=0,lesson=0;
bool shiftNext=false,fnNext=false,passed=false,wrong=false,dirty=true;
const char* flashItem(const char* const* table,uint8_t i){return (const char*)pgm_read_ptr(table+i);}
void line(uint8_t row,const char* text){
 char padded[17]; memset(padded,' ',16); padded[16]=0;
 for(uint8_t i=0;i<16 && text[i];i++)padded[i]=text[i];
 if(strcmp(previous[row],padded)){lcd.setCursor(0,row);lcd.print(padded);strcpy(previous[row],padded);}
}
void render(){
 if(!dirty)return;dirty=false;
 char top[49];
 if(passed){strcpy_P(top,flashItem(outputs,lesson));line(0,top);line(1,"ENTER: next task");return;}
 if(wrong)strcpy(top,"Retry exact task");
 else strcpy_P(top,flashItem(lessons,lesson));
 line(0,top);
 char bottom[17];bottom[0]=fnNext?(shiftNext?'N':'F'):(shiftNext?'S':'>');
 uint8_t start=used>15?used-15:0;
 strcpy(bottom+1,input+start);line(1,bottom);
}
// Only one selected row is driven LOW; all other rows are high impedance.
// Multiple simultaneous closures are rejected until every key is released.
int scan(){
 int found=-1;
 for(uint8_t r=0;r<6;r++){
  digitalWrite(rows[r],LOW);pinMode(rows[r],OUTPUT);delayMicroseconds(50);
  for(uint8_t c=0;c<6;c++)if(!digitalRead(cols[c])){if(found==-1)found=r*6+c;else found=-2;}
  pinMode(rows[r],INPUT);
 }
 return found;
}
void resetInput(){used=0;input[0]=0;wrong=false;shiftNext=fnNext=false;dirty=true;}
void key(int k){
 dirty=true;
 if(k==35){lesson=0;passed=false;resetInput();return;}
 if(k==32){
  if(passed){lesson=(lesson+1)%12;passed=false;resetInput();}
  else {passed=strcmp_P(input,flashItem(lessons,lesson))==0;wrong=!passed;}
  return;
 }
 if(passed)return;
 if(k==33){shiftNext=!shiftNext;return;}
 if(k==34){fnNext=!fnNext;return;}
 wrong=false;
 if(k==31){if(used)input[--used]=0;return;}
 char ch=' ';
 if(k<30){
  ch=pgm_read_byte((fnNext?symbols:normal)+k);
  if(fnNext && shiftNext && k<10)ch=pgm_read_byte(numbers+k);
  else if(!fnNext && shiftNext){if(ch==';')ch=':';else if(ch==',')ch='<';else if(ch=='.')ch='>';else if(ch=='\'')ch='"';else ch=toupper(ch);}
 }
 if(used<48){input[used++]=ch;input[used]=0;}
 shiftNext=fnNext=false;
}
void setup(){
 for(uint8_t i=0;i<6;i++){pinMode(rows[i],INPUT);pinMode(cols[i],INPUT_PULLUP);}
 lcd.begin(16,2);render();
}
void loop(){
 static int candidate=-1,stable=-1;static unsigned long changed=0;static bool armed=true;
 int raw=scan();
 if(raw==-2)armed=false;
 if(raw!=candidate){candidate=raw;changed=millis();}
 if(millis()-changed>=30 && stable!=candidate){
  stable=candidate;
  if(stable==-1)armed=true;
  else if(stable>=0 && armed){armed=false;key(stable);}
 }
 render();
}