Connecting Numeric Keypad to Parallel Port

[geordielads]

Can anyone help me with connecting a numeric keypad (bought from Maplin, JM09K) to my PC via the parallel port.

I'm trying to write an MP3 Jukebox sort of program that uses this keypad to accept a code (like the jukeboxes you get in your local boozer). My program works fine using the normal keyboards numeric keypad but I would prefer using the external one.

The keypad's PCB has 7 contact points below the keypad. I have already ripped my printer cable apart to connect it to an LCD panel, does anyone know which parallel port lins need to be connected to the keypad pins to allow me to recognise the key presses?

Anyones help would be most appreciated.

Thanks
Geordielads

 

[Matt Jason H]

Welcome to PC Review

Pin 1 - 8 are the main inputs to the port, to input to one of these pins you have to gound it. This of course creates problems due to the keypads matrixed design.

I'll see what i can come up with for you

 

[Matt Jason H]

Okay found the perfect solution, its the MM74C922N 16-key Encoder IC. It translates the matrixed keypads outputs into a 4bit signal you can connect to a parallel port.

Rapid Electronics Code: 82-0058

I found a datasheet for you: here

 

[geordielads]

Matt

Thanks for this.

Im not the most Electronic minded person in the world. Can you tell me how this works. Is it just a case of connecting the 7 pins on the Keypad to the first 7 pins on the mentioned chip, and from that connect the chip to the parallel port?

Any chance in a simple diagram?

Cheers
Dave

 

[Matt Jason H]

don't have the required software to make you a schem right now i'm afraid, here's what you'll need to connect:

Pin Connection.
1 Row 1 of keypad
2 Row 2 of keypad
3 Row 3 of keypad
4 Row 4 of keypad
5
6 1uF Capacitor connected to ground
7 10uF Capacitor connected to ground
8
9 Column 3 of keypad
10 Ground
11 Column 2 of keypad
12 Column 1 of keypad
13 To pin 5 of parallel port
14 Positive supply
15
16 To pin 4 of parallel port
17 To pin 3 of parallel port
18 To pin 2 of parallel port
19 To pin 1 of parallel port
20 Positive supply

Consult the data sheer for more information, i'm not sure if you can hook this up directly to the parallel port, i'm researching more into it for you.

 

[geordielads]

Chip is in the post as we speak.

I will let you know how I get on.

Thanks again for your help.
Dave

 

[geordielads]

One last thing,
Im looking for the capacitors, both 1uF and 10uF.
There seems to be a massive range in price, from £2.50 for a pack of 100 to £35 for one. I guess it has something to do with the voltage that these match up to.
1uF/50v radial capacitor - pack of 100 - £2.50
Solid Tant Caps 1uF/40v - pack of 30 - £2
Sub min electrolytic 10uF/25v - pack of 200 - £5
Electrolytic Capacitor Radial 10uF/100v - pack of 25 - £1
up to -> 1uF Capacitor 1000v - £35 each

Now i guess there is no point at even looking at the 1000v (£35) one, but what type and voltage would you suggest?
Do they have to be at 5v like the voltage going to my LCD screen from the PC?

I notice that on the data sheet for the Keypad controller chip it says it can handle anything between 3v and 15v, so do i just get any capacitors between these voltages?

I have been looking at www.greenweld.co.uk for these prices, is there somewhere else that you would suggest? There seem to be a handfull on rapidelectronics, but it doesnt tell you much about them voltage wise.

Can you tell I have never done this before?

Cheers
Dave

 

[Matt Jason H]

You're correct, anything equal to or above the supply voltage is fine, 63v is very common so they might (confusingly) be the cheapest. I use rapid electronics for 90% of my stuff, however www.maplin.co.uk is very good, if you have a store nearby you can save on delivery too.

 

[geordielads]

Matt,

Chip and capacitors arrived. All hooked up, ready to go.
Bugger, didnt work. Not getting anything back to PC. I got a simple program that listens to the printer port and outputs any received data to the screen. Obviously I have done something wrong.

Can you take a quick look at this picture of the circuit (link below) see if i have done anything wrong, connected something to the wrong pins, using the wrong printer port pins (first 5) etc. I appologise in advance for the picture, im as much of an artist as an electrician.
http://www.btinternet.com/~wizzarduk/keypaddiagram.jpg

Cheers
Dave

 

[Matt Jason H]

is that diagram a view from the BACK of the parallel plug?

 

[geordielads]

that view showed the connections going to pins 1-5 on the printer cable. I think they might need to go to pins 10-13 + 15, which is what I have changed them to. I get some strange readings when I do that, but they dont change when the keypad buttons are pressed. they seem to be completely random readings.

 

[Matt Jason H]

I recommend using inpout32.dll i've had great results with it.

More info abotu the dll and how to wire up circuits for it here:
http://www.logix4u.net

 

[MRSAN]

Other keyboard same idea

any idea how to do it with a Welleman 12 KEY KEYBOARD