I decided to play with my keypad. it is a 1-9, 0, *, and # keypad. 3 columns and 4 rows. I got it from the picaxe store (Here) only one difference, there isn't a first or ninth pin. looks a lot like on page 1 of This pdf.
C2-R1-C1-R4-C3-R3-R2 (R = row- C = column)
I was trying to figure out exactyl how to hook this up. I don't know how to hook the pad up to a powersource. I know that it hookes up to the digital ins on my picaxe but I don't know how
you take the columns and hook it up to output pins, and the rows you hook up with input pins (dont forget the pulldowns) (or vice versa). Than you scan the columns (one by one) and look for the rows whether some button is pressed.
ya that was where I got the one I put up from, but i took off the NC’s since they werent on the board they sent me.
I understand the workings now. plus I am quickly understanding the value of slaves. I was hoping to play with my 7segment display and my keypad at once, but the seven segment takes up 8 outputs as it is. do you know of a way to run the 7segment without the slave with less outputs (as for the time being I am limited to my single 28x1).
im getting the fealing that one IC just will never do the trick.
Yes. There is a way to run the both together. There’s nothing to stop the scanning output lines which are used to drive the keypad from also being the data lines to the LCD.
One thing, though: keypad input may make the LCD display a lot of rubbish, so you need to refresh it often.
A note on the keypad: if you intend at any stage to press multiple keys at a time, or if that might happen accidentally, put signal diodes in each of the driver lines. Otherwise, you get a phonomenon called … well, it has a name, which escapes me right now, but you pres two keys on the same row and your decoder thinks you pressed something completely different.
Trouble is, then you can’t use it to drive your LCD (well, you can, but you won’t be able to query it).
so if I am right, you are saying that as long as the refresh rate is high enough (the user may see a blink but nothing substansial) I can have the picaxe test the columns (i have more inputs then outputs at the moment) which are also connected to three of the 8 leds on the 7segment. I can use an interupt to make is so that when the input is finally let go, after the number is correctly output to the display, the number is too.
I don’t completly understand how this methode will produce rubbish in the LCD but I will try it and maybe find out how at that time.
The method would produce rubbish on the screen when keys are pressed because the key presses will be interpreted as LCD data. If you’re trying to write the LCD at the same time as keys are pressed, the data sent will probably be garble.
No. I’m absolutely not recommending a high refresh rate. Just a refresh after every key press. Failing that, get on the modular bandwagon https://www.robotshop.com/letsmakerobots/node/551 and make an I2C interface to the LCD and/or the keypad. That way you can drive both devices using only two pins…!
Once you get this working, I’d be interested to see if you could make it an I2C Module. This is what idaniel was suggesting with the LMR Global Project. I’ve just finished an I²C controller PCB. I’m populating it and developing the software at the moment.
I have a few Ideas on how to make this work on a limited ammount of outputs. after thinking about the solution you gave me earlier I realized that it was flauwed in 1 way,
suppose that the left column and the bottom middle LED of the 7-seg are both connected to out7.
if I push the 1 button I have to maintain the output to out7 in order to check for the user letting go of the button.
while out7 is on the bottom center led is still on this is not good as the number 1 onle uses the right leds
my end solution is mostly programming. give all columns two leads from the out pins. then after checking to see what number is being used, the Picaxe decides (from given inputs) which outs to use making sure to only use 1 ot the columns 2 output pins.
this will only work for the use of pushing a button and loosing the LCD after letting go but i can rethink if for use with modular use. change it to be 2 digits and allowing short term number storage using the pound # and asterisk * symbols for send and delete respectivly
well, I found a rather embarising thing to find. I was looking through the list of picaxe chips and noticed that the chip I have, the 28x1, had 16 outputs. meaning that I could have easilly used both the single digit LCD and the 12 key at the same time. with out any of these problems… lika I said… embarising, lol
I am rethinking a lot of things right now. I tought I could use only one single 28x1 due to my new found 16 outs (14 for the 7 segs leaving out the decimals and 2 for the rows with some creative programming), but then realized I need 2 for the i2c so ill probably use a 28x1 with a serin-slave picaxe-08 for the axtra 3 or four outputs that I need. this gives me the room that I need to work with it and to work comfortably. I would goto a 40x but that doesn’t have any more outputs then the 28x1.
I think I can possibly get the 28x1 to work by itself without a serin-slave but there is an easy chance of glitching and would rather have a module that WONT glitch for sure. ill draw up a plan and code for it anyway.
this will be fun. I have never don I2C before and will learn much.
There have been keypad decoder ICs in the digital logic family, the numbers referenced being 74922 and 74923. Sadly these seem discontinued by most manufacturers. Newark appears to have some Fairchild MM74C922WM at a price of $6.22 each. I don’t know what Newarks minimum order is if they have one. At any rate, it appears to be hooked up something like the keypad row and column pins connected into the IC, and 4 output lines give you a 4 bit number corresponding with the key pressed. As long as the clock is setup, enables set. Other keypad decoders have thrown a cheap mcu at it, which gives another device to program.
For the 7 segment LEDs, not LCDs, another logic IC, the 7447 might be used. This still appears to be manufactured, like the TI SN7447AN, and more findable at $1.85 one place. It is described as a “BCD to 7 segment” decoder. In this case, a 4 bit number is input, to have it displayed on the 7 seg LED. I think I have a couple 74LS47 devices used a while back, pretty easy to hook up.
Using thise logic ICs, it looks like you could go from 21 lines needed, down to 12.
Oh, another thought, found an analog solution to the keypad reading, see this URL :
Read my comment here: https://www.robotshop.com/letsmakerobots/node/131#comment-178 It’s a description of using the 4511 chip which is a bcd to 7-segment display driver. Using this, you can use 4 pins for the data and 2 for the control (selecting display 1 or 2).The 4511 will keep the data until you set it to some other digit. Setting both control lines low, the 4 data pins are available for other things and won’t affect the display, as long as the two enable lines are low.
Great Schematic I love the schematic. At a glance, it looks like something a 5 year olad would do in elementary school using all available colours, but on closer inspection, it looks like a real circuit which stands a fighting chance of working!!
I like the idea of using a sort of resistor ladder to connect the keypad.
Could I be very bold and propose an alternative connection pinout for I2C? The reason is that I’ve already started on my I2C devices and I have 2 boards etched. I thought it might be a good idea if your device was “compatible”? I’m using a 3-wire interface to the main computer which does not involve battery power. My three pins are:
1 - ground
2 - data
3 - clock
You’ve adopted a 5-wire strategy and you may want to stick with that. What would you say to moving your pins around so that the first three are compatible with my schema? Then, I’ll modify my schema to include flexability for the two extra lines.
Pullups: I see you’ve put pullup resistors on the clk and data lines. These are normally provided at only one point in the lines. Since every bus has a master, my suggestion is that you leave them out, but add them to your bus master device. That way you won’t have a load of pullups in parallel if you have multiple slaves.
