DuinoMite, the Arduino Shield Micro-Controller.

by **dangermouse** » Mon May 07, 2012 2:17 am

For a while I've been using a cheap USB keyboard on my Duinomite together with a USB-to-PS/2 adapter.

There's nothing clever inside those little adapters, they're just wires inside.

So I chopped off my USB plug and fitted my own 6-pin mini-DIN connector. It reduces the bulk considerably and looks so much neater. Indeed, having the USB connector and the USB-to-PS/2 adpater looks unwieldy compared to the tiny dimensions of the Duinomite mini.

First I tested the USB-to-PS/2 connector to see what was connected to what. Here it is in colour coded form:

: USB to PS/2 Adapter; USB_PS2_adpater.gif (24.48 KiB) Viewed 6 times

So using the same connection pattern, I connected up the freshly chopped cable to a new PS/2 style connector. The connector is available from many places, I got mine from Farnell:
http://uk.farnell.com/jsp/search/productdetail.jsp?CMP=i-ddd7-00001003&sku=152209

The wires on my keyboard were red, black, white and green. Be aware that other keyboards may use different colours or even the same colours but in different orders. So it's best to use a continuity check on the chopped-off-USB plug to see what connects to what.

Anyway, with my keyboard, I connected it up as so:

: Direct PS/2 keyboard connection; direct_ps2_keyboard_wiring.gif (10.79 KiB) Viewed 10 times

And the result is much neater than using the USB adapter:

: New lightweight keyboard connection; new_ps2_connector.jpg (151.79 KiB) Viewed 10 times

Cheers all,

Jez

by **dangermouse** » Sun May 06, 2012 11:04 pm

Continuing on my theme of getting the most out of a single pin as possible(!), here is a very simple way to monitor a 4×3 keypad (12 keys) using a single analogue input.

: Schematic of 12 key keypad going into 1 analog pin; keypad_schematic.gif (29.64 KiB) Viewed 16 times

The keypad is a standard 12 key type that is already wired as a matrix. It's easy to make your own too out of normal push buttons.

The 4 row wires and the 3 column wires are connected to a few resistors and that then presents you with a single pair of wires whose resistance is completely determined by which key is pressed. Using the values shown in the schematic, the keypad will give you a resistance from 0k to 11k in 1k steps for all 12 keys.

: Keypad with resistors and just 2 wires; keypad_with_resistor_network.jpg (196.94 KiB) Viewed 16 times

By feeding the "keypad resistance" with a constant current source, you end up with a voltage that is linearly affected by the keypad's resistance. This ensures a good spread of voltages with equal steps between them.

: Simple constant current source for keypad; keypad_constant_current_source.jpg (68.35 KiB) Viewed 16 times

It is possible to do away with the constant current source and use a resistor instead but the noise immunity is much worse due to the bunching up of voltages at one end of the curve.

In this implementation it's not possible to sensibly identify multiple simultaneous button presses, but for a keypad, that is rarely required for most applications. A simple combination lock for example will never need more than 1 key pressed at a time.

Code: Select all

Cls

						SetPin 1,1              'Pin 1 is analogue input

						SetTick 10,timer_int    'Sample keypad every 10mS

						Font #2,2

Do If keypress$<>"" Then 'This variable is set with a keypress on the keypad Print keypress$; 'Print the keypress on the screen keypress$="" 'Clear that keypress, ready for next one. EndIf Loop Until Inkey$<>""

End

timer_int: 'This is called every 10mS to sample the pin(1) volts 'Only keys that generate 2 consequetively identical 'key codes will be considered valid. 'Jitter and errors are automatically eliminated. 'Valid keypressed are put into keypress$ maxR=11 'Max keypad resistance in kOhms constcurrent=0.246 'Current source in mA vkey=Pin(1) keynum=Cint(vkey*11/(maxR*constcurrent)) 'Convert to nice integer keypattern$="2315648970#*xxx" 'Keymapping for keypad resistances keyhistory$=Right$("xxxx"+keyhistory$+Mid$(keypattern$,keynum+1,1),4) If Right$(keyhistory$,3)="xxx" Then keyoff=1 If keyoff=1 And Mid$(keyhistory$,3,1)<>"x" And Mid$(keyhistory$,4,1)<>"x" Then If Mid$(keyhistory$,3,1)=Mid$(keyhistory$,4,1) Then keypress$=Right$(keyhistory$,1) keyoff=0 EndIf EndIf

IReturn

The software measures the input voltage with a 10mS interrupt and converts it to an integer representing 0 to 11 (12 values). In fact a value of 13 is generated for "no key press". That integer is then converted to a specific key by using a simple string pattern and mid$.

The keypress is then stored in a rolling history string (called keyhistory$) that is 4 characters long and is updated every 10mS. This is used to eliminate errors, provide debouncing and to correctly identify the actual keypress event (and key release event).

Any keypress is automatically plopped into keypress$. So to get a keypress, just inspect keypress$ and see if it's null or not. If it's not null then it contains a valid keypress event. When you've got that keypress, make sure you clear it by keypress$="" to make way for the next keypress.

The program here simply shows this all working and displays the keypresses in big characters on the screen.

It works very reliably and has seems to suffer from no mis-reads at all, even with 10m of bell wire between the keypad(and resistor network) and the main circuit!

I hope it's of use to someone.

Jez

PS. This software is for MMBasic V3.2A (other V3.x may also work).

SetPin #	I/O Type	Maximite GPIO Pin()	DuinoMite GPIO Pin()
1	Analog Input	1-10	1-7,19,20
2	Digital Input	1-20; (11-20 are 5V tolerant)	1-10, 12-20; (8-10, 13-18 are 5V tolerant)
3	Frequency Input	11-14	5-7
4	Period Input	11-14	5-7
5	Counting Input	11-14	5-7
6	Interrupt (L-H)	1,2,10-14	1,2,5-7
7	Interrupt (H-L)	1,2,10-14	1,2,5-7
8	Digital Output	1-20	1-20
9	Digital Output (+5V Open Collector)	11-20	8-10,13-18

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