Help with matrix keypad

[01dabreoo]

hi, i was wondering if anyone could help me.
for my AS project i have designed a very simple combo lock,
its basically just some 555 monostables and some 2 input NAND gates, one input of the nand gate is connected to Vs, so when the 555 output goes high the output of the nand with go low, the ouput of the nand gate it connected to the trigger of the 555 with a switch inbetween so that u have a set time you can press the switch before the first 555 turns on, this happens for 4 switches.
I am trying to replace the switches with a keypad, but the only keypad i could get hold of was a matrix one which i dont know how to use, you anyone explain how i could use it?
here is the keypad - **broken link removed** and it also comes with 2 pdf's with 2 different pin outs **broken link removed** **broken link removed**

thank you

 

[suicidalmonkey]

There are 12 buttons on the keypad, in the formation
1 2 3
4 5 6
7 8 9
* 0 #

Each button is part of one row and one column (ie. 8 is in the thrird row and second column).

So if the number 8 is part of your code you need to connect the row three and column two pins in place of the switch.

 

[-=GST=- Nemisis (cs/cz)]

yeh i have used that keypad, i was confused how it worked at first but its quite simple. you are probably gunna need a pic because of the way it works. a matrixed keypad is basically a load of switches between the columns and the rows, i made mine work by sending one column high and checking if any rows were high, because if a button has been pressed it will send the corresponding row high, if not sending the next column high and checking if any rows were high. that you can tell which button is pressed by the combination of which row and column is high. if you do this for A-level i recommend using a PICAXE or a logicator system if you havent learnt a programming language. if you use picaxe i can even send you the code for it.

 

[01dabreoo]

There are 12 buttons on the keypad, in the formation
1 2 3
4 5 6
7 8 9
* 0 #

Each button is part of one row and one column (ie. 8 is in the thrird row and second column).

So if the number 8 is part of your code you need to connect the row three and column two pins in place of the switch.

thats what i thought but it doesnt work, it will either work when you press the button and also when you press another button, or it will just do nothing.

yeh i have used that keypad, i was confused how it worked at first but its quite simple. you are probably gunna need a pic because of the way it works. a matrixed keypad is basically a load of switches between the columns and the rows, i made mine work by sending one column high and checking if any rows were high, because if a button has been pressed it will send the corresponding row high, if not sending the next column high and checking if any rows were high. that you can tell which button is pressed by the combination of which row and column is high. if you do this for A-level i recommend using a PICAXE or a logicator system if you havent learnt a programming language. if you use picaxe i can even send you the code for it.

the problem is i need it to be low, also i have no idea of programing i think that is covered next year.
here is a circuit - **broken link removed**

 

[-=GST=- Nemisis (cs/cz)]

i know why you cant blood well use it, its because u have the pins mixed up. grr i had this problem for a day when i relaised it wasnt my fault it was rapid electronics. alright ill explain it for u, from left to right the pins are like this

pin 1 (far left) = column2
pin2 = row1
pin3 = column1
pin4 = row4
pin5 = column3
pin6= row3
pin7=row2

this is confusing but its how it works. however i dunno how using a keypad will work in your system, i dont think it will work because you need 4 switches and if you have the 3 columns connected as one side of the switch and a row connected as the other side (which is what i think u are trying??) you will only have 3 switches which defeats the point of having a keypad, this system should not use a kepad by rights anyway.

this is what i think you are trying, you want the system to have a keypad wiht its column/row switches connected as switches to these 555s and the user needs to press one number (connecting the switch) then another and another for each 555 in the timelimit created by the 555s as if there was a combination that must be entered in a timelimit? tell me if i am right.

if this is indeed what you are trying then it is fundementally flawed, firstly because it would be impossible with this keypad due to the way it works, a 3 number combination lock would work but it still a poor system. u could get a 4x4 keypad with hex numbers but this is not a good way to make a combination lock system. the other problem would be that a person could just button bash and press every button between each 555 timelimit, there should be some sort of system where the user is locked out if they get it wrong (tho there doesnt have to be, mine didnt but i suggested multiple ways of doing it in my limitations, lots of extra marks). also this means that the system isnt programmable which is important for a good combination lock.

inst your coursework supposed to be in very soon tho? mine is supposed to be in on the 17th of this month. also not trying to be rude but your circuit is very simple for a combination lock, i did the same thing for mine and it was programmable and played a tune and all sorts, if you want to spice it up a bit i could help because i did the same project last year and got an A

Edit: also if u are doing the same course as me u will not learn programming but you will learn some Q basic commands which is fairly useless. for making PIC code at a starter level i would go with PICAXE because its really really really easy and take like 5 minutes to learn and 30 minutes to master and has one of the simplest programming systems ever. check out www.picaxe.com and the software is free.

 

[01dabreoo]

i know its not very good i wanted to use what i hae learnt from the course to make one, to stop it from working if u mashed all the keys i would wire up the reset pins on the 555s to the unused numbers.
it does need to be in after easter i have done the write up and built it, but i just couldnt get the keypad to work.
i was thinking some sort of logic system would work? ill think about it today

 

[-=GST=- Nemisis (cs/cz)]

you could use a 74C922 IC which will decode the keypad into binary and then use logic gates to make the rest of the system work. doing this would get you alot of extra marks.

 

[01dabreoo]

Ok, i will give that a try.
do you know anywhere that will be able to delivery for monday?

 

[01dabreoo]

seen one from rapid, to get it next day it will cost around a 10er, i feel its quite a bit but at the end of the day it will be worth it.
how would i use this thing?