Post by thread:[PICLIST] Scanning a 4x4 keypad

Dear All You must forgive me if this seems to be a very basic question, but I am having trouble working out this concept. I know that it is possible to scan a 4x4 keypad using 4 inputs and 4 outputs of, for example a 16F876. What I am having trouble with is wheter it is better to use interrupts, or just a straight scanning regime. Can anyone give me some advice on this, please? Peter Reynolds - For the latest in IT Services Synstar Business Continuity Check out our NEW web site Technical Consultant http://www.synstar.com 020 738 82888 Ext.7994 This communication contains information that is confidential. It is for the exclusive use of the intended recipient. If you are not the intended recipient, please note that any distribution, copying, or use of this communication, or the information in it, is prohibited. If you have received this communication in error, please notify me by e-mail or by telephone, and then delete the e-mail and any copies of it. -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

Peter Reynolds wrote: > > Dear All > > You must forgive me if this seems to be a very basic question, but I am > having trouble working out this concept. I know that it is possible to scan > a 4x4 keypad using 4 inputs and 4 outputs of, for example a 16F876. What I > am having trouble with is wheter it is better to use interrupts, or just a > straight scanning regime. Can anyone give me some advice on this, please? > > It sounds to me the problem you have is when to check for key press and how many times and how to tie the scanning into the rest of the program? Best is not to initially scan the keypad everytime to get keypress. Call a subroutine where you make all the scan lines high, then read the inputs to see if any of them is high (or set) This takes up minimum steps. If any is, then you start scanning to see which key it is. If not return to rest of program. Or as you say, use the interupt of portB and then run key scanning in the interupt routine. Just leave all your scan lines high (or set) though. The choice is yours depending if you want to interupt your program and at what level. First example gives you more control but the second is more automatic. Quentin -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

> > Dear All > > You must forgive me if this seems to be a very basic question, but I am > having trouble working out this concept. I know that it is possible to scan > a 4x4 keypad using 4 inputs and 4 outputs of, for example a 16F876. What I > am having trouble with is wheter it is better to use interrupts, or just a > straight scanning regime. Can anyone give me some advice on this, please? Better is so subjective. Much better to be concerned with good enough. Good enough is when the application performs the task required. The basic question here is what else needs to be done other than the keyboard. If the rest of the application is driven by the keyboard input then it's perfectly acceptable to sit and wait for keyboard presses in a loop then respond to them. However if there's other stuff going on then an interrupt based system allows for those other activities to occur while waitint for keyboard input. Keyboards are very slow devices. Even a 50ms timer interrupt is sufficient for monitoring a keyboard. Hope this helps, BAJ -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu

On Sat, 2 Dec 2000 15:58:10 +0200 Quentin <.....qscKILLspam.....ICON.CO.ZA> writes: > > Best is not to initially scan the keypad everytime to get keypress. > Call > a subroutine where you make all the scan lines high, then read the > inputs to see if any of them is high (or set) This takes up minimum > steps. If any is, then you start scanning to see which key it is. If > not > return to rest of program. > > I like polling in an interrupt (a timer interrupt). That way you get pretty uniform response time. I agree that you should first poll to see if ANY key is down. My normal practice is to do as above, but reverse. Since inputs float, you have to either pull them up or down with a resistor (or the weak pull-up on port B). I tend to use pull-ups (often those on port-B). So, set all the output lines driving the keyboard low, then look for a low on any of the input lines. If there is no low, you can exit immediately, since no key is down. If there is a low, you can determine which row or column (depending on how you've connected the keyboard) based on which line is low. Then drive each output low sequentially to find which column or row (again, depending on wiring) is pressed. If each scan yields the same scan code, decrement a debounce counter. When the debounce counter hits zero, flag that you've got a key. Harold FCC Rules Online at http://www.hallikainen.com/FccRules/ ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: dl.http://www.juno.com/get/tagj. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Harold Hallikainen wrote: > If each scan yields the same scan code, decrement a debounce counter. > When the debounce counter hits zero, flag that you've got a key. Thanks! That's very clever. I have always done it by checking for valid keypress and then using a timed debounce delay. Using a decremented counter for scan combination on every scan is a great idea and something I never would have thought of. :o) -Roman -- 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

Well here we go again, >Harold Hallikainen wrote: > >> If each scan yields the same scan code, decrement a debounce counter. >> When the debounce counter hits zero, flag that you've got a key. > >Roman Black replyed: >Thanks! That's very clever. I have always done it by checking >for valid keypress and then using a timed debounce delay. Using >a decremented counter for scan combination on every scan >is a great idea and something I never would have thought of. :o) >-Roman Well Scott's 'vertical counters' is a very nice piece of s/w for this kind of thing :) Look at his site or in the piclist site ( for example on pic->i/o->keyboard ) /Tony Tony Kübek, Flintab AB ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² E-mail: EraseMEtony.kubekspam_OUTTakeThisOuTflintab.com ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² -- 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

K|bek Tony wrote: > Well here we go again, > >Harold Hallikainen wrote: > > > >> If each scan yields the same scan code, decrement a debounce > counter. > >> When the debounce counter hits zero, flag that you've got a key. > > > >Roman Black replyed: > >Thanks! That's very clever. I have always done it by checking > >for valid keypress and then using a timed debounce delay. Using > >a decremented counter for scan combination on every scan > >is a great idea and something I never would have thought of. :o) > >-Roman > > Well Scott's 'vertical counters' is a very nice piece of > s/w for this kind of thing :) > Look at his site or in the piclist site ( for example > on pic->i/o->keyboard ) > Where is the link for this site??? Thanks! {Quote hidden}> > /Tony > > Tony K|bek, Flintab AB > 222222222222222222222222222222222222222222222222222222222222 > E-mail: tony.kubekspam_OUTflintab.com > 222222222222222222222222222222222222222222222222222222222222 > > -- > 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 -- 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

Hi, I wrote: >> Well Scott's 'vertical counters' is a very nice piece of >> s/w for this kind of thing :) >> Look at his site or in the piclist site ( for example >> on pic->i/o->keyboard ) >> William replyed: > Where is the link for this site??? > > Thanks! Ok, thought it was general knowledge :) but here goes: Here's Scott's original code: ( look at pic_debounce ) http://www.dattalo.com/technical/software/software.html Here an 'real-world' implementation of it: http://www.piclist.com/techref/microchip/picboard.htm A bit bloated agreed, but fully functional. The thing is that the benefits of vertical counters are not really obvious at first. But once you start using them you really see what could be done with them. There are easier ( and more ram conservatory ) implementations available but inregards to programflow they are really hard to beat. Particulary as there are *NO* delays needed for the debounce. Using the timer or the mainloop itself (for the sample delay) one just grab an sample of the keyinput feed it to the debounce routine check the output. etc etc.. /Tony Tony Kübek, Flintab AB ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² E-mail: @spam@tony.kubekKILLspamflintab.com ²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²²² -- 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