View Full Version : 'shifting' LED readouts

04-21-2007, 01:25 PM
I am new to this game.· Am wondering the 'how to' of repositioning a series of digits posted on a 7 segment led to 'jump' to another Led set.

Picture this...

I hook up a keypad and have a series of digits read onto a 7 segment readout.· Say its 8 digits in length.

Now, I want the ENTIRE sequence of 8 digits to 'appear' on a separate bank (B)·of 7 segment while they 'disappear' from the original bank (A).· All at a keypad stroke.· This will allow me to enter an
entirely set of 'new' digits into the keypad for display on the original screens (A).· If I hit the 'magical keypad button' again, the NEW digits jump over and replace the previous digits on the secondary screen (B) and leave the original banks (A) free for more input.




04-21-2007, 09:58 PM
Do your readouts have latches to hold the digits?
Is the data sent to the readouts serially?

Mike Green
04-21-2007, 10:13 PM
This does all depend on how you send digits to the readouts in the first place. Typically, you either have some kind of controller or latches to hold or multiplex the decoded digits (translated to 7 segment format). To change the display, you have to send the same information that was on A to whatever hardware is on B and effectively blank out or send new digits to A. The details of how this is done depend on the hardware involved.

Do you have some kind of display in mind?

04-21-2007, 11:17 PM
I am recreatingt this silly box as in the photo.· Still in the 'how do it do it' thinking stage.

Was thinking of multiplexed 7 segments.· Need still the 'months' on a 16 segment, and thats a whole other issue :)

I have a goal and am sure that I will eventually get there.· I am new to this whole game but seemed to handle the parallax intro kit pretty well.

If you were building this thing, what controller would you use for the leds?· I have read a bit about some maxim chips (7219 ect) that I hope will work.

I love the challenge and am glad found this forum.· You guys are very nice.

The 'shift' or 'jump' will occur when I want to input new data on the top line.· The entire top line then 'reappears' on the bottom line.· The middle line is just a clock and I was thinking of a pocketwatch B for that if it makes sense.


Post Edited (MikeX) : 4/21/2007 4:28:59 PM GMT

04-21-2007, 11:34 PM
That should be easy after you get the flux capacitor installed...you do have your capacitor don't you?

- Stephen

04-21-2007, 11:40 PM
Thanks...um...I guess.· I started with that part of the car, silly.· The Time Circuit is my missing piece at this time.·

At least we both have the same motivations.


Mike Green
04-21-2007, 11:53 PM
Have a look at this display driver: datasheets.maxim-ic.com/en/ds/MAX6955.pdf (http://datasheets.maxim-ic.com/en/ds/MAX6955.pdf)

It looks like it could easily do what you want (mixed 7 segment and 16 segment displays with an internal character generator for both formats). You might be able to get a sample from Maxim ... check their website ... and it comes in a PDIP package for ease of breadboarding.

I would suggest using a BS2p or BS2pe for a controller since the display chip uses I2C. The BS2p series Stamps have a convenient built-in I2C send/receive statement. The other Stamps have to do I2C using subroutines ... doable, but not as convenient.

There's a similar chip, the MAX6954 (datasheets.maxim-ic.com/en/ds/MAX6954.pdf (http://datasheets.maxim-ic.com/en/ds/MAX6954.pdf)), which uses SPI for it's data. This is a 3-wire system that's easily handled with any Stamp model including the BS2.

Post Edited (Mike Green) : 4/21/2007 4:59:09 PM GMT

04-23-2007, 06:57 AM

Where can I learn more about this IC2 setup (used in the BS2p apparantly) as suggested with the Maxim 6955?· Im interested in learning how to utilize it, but am much better with diagrams and hand holding.·



Bruce Bates
04-23-2007, 11:35 AM
Mike -

I2C is a proprietary access method which is owned by NXP (formerly Philips Semiconductor). As you will learn at the link provided below, a tight control is maintained by NXP on the numerous device assignment numbers, the protocol is both robust and rigid by design, it can operate at more than one speed, and it permits a wide variety of devices to exist on one single bus. In addition, multiple busses are possible, and multi-speed busses can exist as well. So too 3.3 volt and 5.0 volt systems connected end-to-end.

Here is everything you ever wanted to know about I2C and then some, including the entire I2C Specification Document (bring lunch!):



Bruce Bates


05-24-2007, 02:20 PM
Is there a sample PBasic code showing how to use keypad inputs and correlate them into the maxim led driver chip?·


05-25-2007, 01:21 AM

Do you really need all those LED displays, drivers, mounting hardware, case, power supplies, etc., etc.? Or would a simple 4 x 20 character LCD display also do the trick?

I'm just thinking out loud here.


06-18-2007, 02:05 PM
Yeah, Im building the box just like the one shown there.· Old school LEDS.· Wish I could settle for LCD, but I need the screen visible in all lighting conditions, just as the original.

06-22-2007, 10:32 PM
Yipe! $24 for that puppy from DIGIKEY... Awesome that MAXIM made this device though. I always assumed that nobody would ever make a chip like this. I'm now formulating my own ideas for how to use it. I love it when people know the easiest way to solve a problem and are willing to share.