Post by thread:[OT:] different approach to keyboard scanning?

source= http://www.piclist.com/postbot.asp?id=piclist\2003\04\11\174744a Let me see if I have all this right. Combining Scott and Eric's comments you could do this: 0 1 2 3 GND | | | | | 0---+--KEY-KEY-KEY-KEY- | | | | | 1---+---+--KEY-KEY-KEY- | | | | | 2---+---+---+--KEY-KEY- | | | | | 3---+---+---+---+--KEY- | | | | | Weak pull-ups enabled, first read the port and check for any lows, this would be a key on the GND (far right) column. If all pins are high, ground pin 0 and any lows on 1 thru 3 would be a key in the top row. Then ground 1 and a low on 2 or 3 indicates the two keys on the second row (other than the last column), finally ground 2 and check the remaining key (on the third row) by reading back 3. That is a 10 key pad in 4 IO lines with no external components other than the keys. --- James Newton: PICList.com webmaster, former Admin #3 spam_OUTjamesnewtonTakeThisOuTpiclist.com 1-619-652-0593 phone http://www.piclist.com/member/JMN-EFP-786 PIC/PICList FAQ: http://www.piclist.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

part 1 2888 bytes content-type:text/plain; (decoded 7bit) Would you believe you can read 75 switches with 5 I/O lines? Check out the attached Word doc. It has a couple methods for reading many switches with few I/O lines. ----- Original Message ----- From: "Herbert Graf" <.....mailinglistKILLspam@spam@FARCITE.NET> To: <PICLISTKILLspamMITVMA.MIT.EDU> Sent: Saturday, April 12, 2003 6:37 PM Subject: Re: [OT:] different approach to keyboard scanning? > Wow, thanks for the summary, I didn't notice this thread until now. That is > an excellent design! 10keys with only 4 I/O ports used!?? Gonna file this > one in my "info" file... TTYL > > > {Original Message removed} part 2 29221 bytes content-type:application/msword; (decode) part 3 2 bytes -

PLease do not send Word attachments. Can you resumit as text/gif Stuart ----- Original Message ----- From: "Carey Fisher - NCS" <.....ncsKILLspam.....NCSRADIO.COM> To: <EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU> Sent: 14 April 2003 06:07 Subject: Re: [OT:] different approach to keyboard scanning? {Quote hidden}> Would you believe you can read 75 switches with 5 I/O lines? Check out the > attached Word doc. It has a couple methods for reading many switches with > few I/O lines. > > > ----- Original Message ----- > From: "Herbert Graf" <mailinglistspam_OUTFARCITE.NET> > To: <@spam@PICLISTKILLspamMITVMA.MIT.EDU> > Sent: Saturday, April 12, 2003 6:37 PM > Subject: Re: [OT:] different approach to keyboard scanning? > > > > Wow, thanks for the summary, I didn't notice this thread until now. That > is > > an excellent design! 10keys with only 4 I/O ports used!?? Gonna file this > > one in my "info" file... TTYL > > > > > {Original Message removed}

> -----Original Message----- > From: Herbert Graf [SMTP:KILLspammailinglistKILLspamFARCITE.NET] > Sent: Saturday, April 12, 2003 11:38 PM > To: RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU > Subject: Re: [OT:] different approach to keyboard scanning? > > Wow, thanks for the summary, I didn't notice this thread until now. That > is > an excellent design! 10keys with only 4 I/O ports used!?? Gonna file this > one in my "info" file... TTYL > > Dennis Crawley recently posted a complete project using an idea I had a few years back at http://www.mikerj.clara.net/keypad.html . The subject was [PIC]:4x4&LCD in 1port Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to spamBeGonepostmasterspamBeGonebookham.com. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

{Quote hidden}>From: "James Newton, webhost" <TakeThisOuTjamesnewtonEraseMEspam_OUTPICLIST.COM> >source= http://www.piclist.com/postbot.asp?id=piclist\2003\04\11\174744a > >Let me see if I have all this right. Combining Scott and Eric's comments >you >could do this: > > 0 1 2 3 GND > | | | | | >0---+--KEY-KEY-KEY-KEY- > | | | | | >1---+---+--KEY-KEY-KEY- > | | | | | >2---+---+---+--KEY-KEY- > | | | | | >3---+---+---+---+--KEY- > | | | | | > >Weak pull-ups enabled, first read the port and check for any lows, this >would be a key on the GND (far right) column. If all pins are high, ground >pin 0 and any lows on 1 thru 3 would be a key in the top row. Then ground 1 >and a low on 2 or 3 indicates the two keys on the second row (other than >the >last column), finally ground 2 and check the remaining key (on the third >row) by reading back 3. Unfortunately you don't get n-key rollover this way (something I require, but that's just me), so you might as well fill in the lower half of the triangle and get 16 keys, no? 0 1 2 3 GND | | | | | 0---+--KEY-KEY-KEY-KEY- | | | | | 1--KEY--+--KEY-KEY-KEY- | | | | | 2--KEY-KEY--+--KEY-KEY- | | | | | 3--KEY-KEY-KEY--+--KEY- | | | | | Btw, why did this thread become [OT]? Should I have marked my original query [OT]? _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

4/14/03 10:32:52 AM, Michael Park <RemoveMEmp__TakeThisOuTHOTMAIL.COM> wrote: >Unfortunately you don't get n-key rollover this way (something I require, >but that's just me), so you might as well fill in the lower half of the >triangle and get 16 keys, no? > > 0 1 2 3 GND > | | | | | >0---+--KEY-KEY-KEY-KEY- > | | | | | >1--KEY--+--KEY-KEY-KEY- > | | | | | >2--KEY-KEY--+--KEY-KEY- > | | | | | >3--KEY-KEY-KEY--+--KEY- > | | | | | Won't work, unless you put diodes in series with the keys. Otherwise, there's no way to distinguish between, say, the first key (going left-to-right and top-to-bottom) from the fifth key; they're both at the intersection of port bit 0 and port bit 1. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hello, I've been thinking about using the PIC A/D to scan a 16 keys keyboard. The example bellow have only 4 keys for simplicity: ,----K1----VDD | 1k | +----K2----VDD | 1k | +----K3----VDD | 1k | ADC----+----K4----VDD | 1k | GND Without any key pressed, the ADC would read 0V, with K1 pressed it would be 1.25V, with K2=1.66V, K3=2.5V, K4=5V. I think this would be very interesting for projects using a PIC with ADC and short of I/O. Best regards, Brusque -- ----------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Research and Development Blumenau - SC - Brazil Say NO to HTML mail http://www.citronics.com.br ----------------------------------------------------------------- -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestEraseME.....mitvma.mit.edu>

Edson Brusque wrote: {Quote hidden}> Hello, > > I've been thinking about using the PIC A/D to scan a 16 keys > keyboard. The example bellow have only 4 keys for simplicity: > > ,----K1----VDD > | > 1k > | > +----K2----VDD > | > 1k > | > +----K3----VDD > | > 1k > | > ADC----+----K4----VDD > | > 1k > | > GND > > Without any key pressed, the ADC would read 0V, with K1 pressed > it would be 1.25V, with K2=1.66V, K3=2.5V, K4=5V. > > I think this would be very interesting for projects using a PIC > with ADC and short of I/O. > > Best regards, > > Brusque Other than that, look this design we made and used 11 years ago; http://www.ustr.net/electronics/akeys.shtml Wagner. -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestmitvma.mit.edu>

Another method is to use an R / 2R ladder configuration. That allows you to have multiple key presses or chording. There is a real limit due to resolution of the converter and accuracy of the components but this method lets you use resistor networks and the absolute value is less important than the match between components. 4 buttons allows 16 combinations and works well with a PIC 8 bit converter. I did this 7 or 8 years ago and many of you probably have used the product it is in. Larry At 10:34 AM 4/16/03 -0400, Wagner Lipnharski wrote: {Quote hidden}>Edson Brusque wrote: > > Hello, > > > > I've been thinking about using the PIC A/D to scan a 16 keys > > keyboard. The example bellow have only 4 keys for simplicity: > > > > ,----K1----VDD > > | > > 1k > > | > > +----K2----VDD > > | > > 1k > > | > > +----K3----VDD > > | > > 1k > > | > > ADC----+----K4----VDD > > | > > 1k > > | > > GND > > > > Without any key pressed, the ADC would read 0V, with K1 pressed > > it would be 1.25V, with K2=1.66V, K3=2.5V, K4=5V. > > > > I think this would be very interesting for projects using a PIC > > with ADC and short of I/O. > > > > Best regards, > > > > Brusque > > >Other than that, look this design we made and used 11 years ago; > >http://www.ustr.net/electronics/akeys.shtml > >Wagner. > >-- >http://www.piclist.com hint: To leave the PICList >RemoveMEpiclist-unsubscribe-requestEraseMEEraseMEmitvma.mit.edu Larry G. Nelson Sr. RemoveMEL.Nelsonspam_OUTKILLspamieee.org http://www.mchipguru.com -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTspammitvma.mit.edu>

It works like a D/A with each switch being a binary count input. 1,2,4,8,... The number represented by the switch combo is translated to an analog value by the R/2R ladder and the A/D reads the value. You use a look up table type of code to determine the switch combo ie if between 1.05 and 1.35 it is switches 3 and 5 or some such value you have calculated. The problem is in the number of switches. Theoretically you can use 8 switches with an 8 bit converter but with tolerances and noise I usually have 4 or 5 that I set as a limit. Larry At 02:24 PM 4/16/03 -0500, you wrote: >Just saw this approach, and wondered how does one know which combinations >are presed? > > >And how can one press all 4 buttons at once and get correct output? > >{Original Message removed}

Michael Park wrote: > Unfortunately you don't get n-key rollover this way (something I require, > but that's just me), Most keyboards no longer use diodes to achieve n key roll over. (Many also only support 2 or 3 key rollover) They do it by by tracking in software what they know the previous state of the keyboard was and comparing the current scan with the previous one and logically determining what was pressed in between. w.. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics