Re: BTEC Course - Exercise 9 Program 1 Part 2 - Keypad program

The G · Post by **The G** » Tue Jan 16, 2018 12:48 pm

Hi,

Until there is a dedicated BTEC section, I'll start off the topics with BTEC Course so that it's easy to find and move later if necessary...

I am not a skilled programmer so please go easy on me! I am working through the exercises in your guide: http://www.matrixtsl.com/resources/file ... course.pdf

As per Exercise 9 Program 1 Part 2 - When reading inputs from the keypad, how do you do this without using the macros?

Post by **Benj** » Tue Jan 16, 2018 2:01 pm

Hi G,

If I am reading this correctly you are asking how the component macros work to sample the keypad.

The keypad macros basically do a scan of the keypad pins by performing the following.

We set one of the column pins high and the rest are driven low. We then read the input values of the row pins checking for a logic high which would indicate a switch press on that column. We then repeat this for the rest of the columns.

If we get a logic high back then we use a look up table to translate the switch index ((column * numrows) + row) into the corresponding ASCII value.

The G · Post by **The G** » Wed Jan 17, 2018 5:01 pm

Benj wrote:Hi G,

If I am reading this correctly you are asking how the component macros work to sample the keypad.

The keypad macros basically do a scan of the keypad pins by performing the following.

We set one of the column pins high and the rest are driven low. We then read the input values of the row pins checking for a logic high which would indicate a switch press on that column. We then repeat this for the rest of the columns.

If we get a logic high back then we use a look up table to translate the switch index ((column * numrows) + row) into the corresponding ASCII value.

Ah thanks, ok I think I understand the theory behind it from your explanation, so how would that be entered into the input box for example, if I want to only read the "5" button in order to assign it a different character, without the use of a macro. Essentially using the keypad just as a set of generic buttons.

Post by **Benj** » Thu Jan 18, 2018 4:24 pm

Hi G,

You can't read all the buttons directly without doing the scanning technique. So you can't simply use an input icon to read the state of a specific button. However you can pair the input with an output and this should work for polling a single button or column of buttons.

If you just wanted to scan button 5 as per your example then you would have to output a 1 to column 1 (port bit 1) and a 0 to columns 0 and 2 (port bits 0 and 2). You can then use an input icon to check state of row 1 (port bit 5).

output 0b00000010 with mask 0b00000111
input with mask 0b00100000

Hope this helps and makes sense.

The G · Post by **The G** » Thu Jan 18, 2018 4:58 pm

Thanks, I'll try that!

The G · Post by **The G** » Wed Jan 24, 2018 4:07 pm

I've tried my best to solve this, but it is outside of my ability!

I don't know if the person who wrote the course guide is on the forum, but could you please provide an answer program for this task on page 26 - Exercise 9 as per the highlights line on the image attached. Thanks!

: Program without Macro.JPG (76.29 KiB) Viewed 13072 times

Post by **Steve** » Thu Jan 25, 2018 11:12 am

To solve this you will need to refer to the datasheet:
http://www.matrixtsl.com/resources/file ... 4-30-1.pdf

The switches are arranged in a 4x3 matrix - 4 rows and 3 columns. The basic procedure to detect the key pressed is as follows:

output '1' to column pin 1 and '0' to column pins 2 and 3
read each row pin in turn
if the input is '1', then you know the switch at that column and row intersection is pressed
if no keys in that column are pressed, repeat the procedure for the other columns

So if you get a logic high ('1') when reading row 2 when column 2 is activated, you know the key pressed is number 5.

I hope this will go part of the way in helping.

Regards,
Steve.

The G · Post by **The G** » Thu Jan 25, 2018 1:21 pm

Hi Steve,
Thanks, and yes I understand the theory completely.
I am finding this very frustrating as a first time teacher in this topic. It feels embarrassing at times actually.
Anyway, I have tried again and still cannot do this.
I have attached one of my 47 attempts (yes 47 I kid you not.)
Please assist

Keypad Signal 33.fcfx: (9.19 KiB) Downloaded 421 times

Post by **LeighM** » Thu Jan 25, 2018 2:29 pm

Hi,
The row read needs to read different pins to the column write.
So I've changed the mask in the read icon.
Hope that helps

Post by **medelec35** » Fri Jan 26, 2018 11:33 am

Hi, I have created a routine which should work on hardware, well works perfect with Proteus Simulation:

Keyscan routine1.png: (68.31 KiB) Downloaded 4401 times

See if you can understand with whats going on just single stepping into code (F8) then watching the variable values change.

There maybe other better ways, but it's just what I thought of at the time.

Martin

Edit: Confirmed working on hardware.

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