Basic STAMP Module or BS2-IC with a Super Carrier board???

Mitch

Fellow STAMP Enthusiasts:

I am looking at building a special purpose calculator for my daughter who has a learning disability. She has problems figuring out the denominations of currency that she needs to give back to customers at her job an by extension has problems determining, quickly, what denominations to expect in return from her purchases.

Here's my idea...maybe not very original, but I couldn't find a calculator like it when doing Google searches.

I want to build a calculator that she can enter the "total charges", the amount given and have the display show her the correct change and the denominations in $20/$10/$5/$1/.25/.10/.05/.01. I would also like to incorporate a calculator and learning mode.

I envision having a STAMP at the heart of the device, and the 4x20 Backlit LCD for output and the S-Cubed 4x4 keypad processes by the MEMkey decoder. My main questions, at this point, is one of which Stamp module /c carrier board.

I think that the Basic STAMP module would probably suffice to run the Decoder and LCD, because of the minimal pin requirements. I have concerns that the 256 memory for insstructions may not be enough to do everything I want the calculator to do.

Although I like the additional code memory of the BS2-IC, I really like the small footprint of the BS-1 module. Although, because of the size of the keypad and the LCD, the Super Carrier Board may still fit.

Anyone out there have any experience with these components??? Am I seeing problems that don't really exist? Anyone have any suggestions???

I have plenty of programming experience, I think I can figure it out; especially if I have some sample code snippets to look at. Although I am not an EE, I can usually figure things out from a schematic (which I don't see as being too involved for this one).

Thanks in advance,
Mitch

Mike Green

The BS1 is not going to be adequate for more than handling the LCD and keypad. It's really quite small in terms of how complex a program it can hold. For controlling a motor or something simple without much decision making, it's quite adequate. I would suggest using one of the larger Stamps with built-in commands for the LCD (assuming it's a parallel LCD controller). The BS2p, BS2pe, or BS2px would all do. I'd go with the BS2px ("biggest, fastest, latest and greatest") since there's not much difference in the price. If you're doing your development on a Mac, there's no compiler yet for the BS2px, so you'd have to use a BS2p or BS2pe. With a Windows PC, you can use the BS2px. The Super Carrier Board is also an excellent choice. I've used several of them over the last few years and both the BS2p and BS2pe for different projects. Look at the Nuts and Volts articles in the Parallax book section. There's one article on interfacing to an LCD and several on interfacing to 4x4 keypads, all with sample code.

Mike Green

Chris Savage

Mike,

·· One pitfall to jumping right in with the latest and fastest Stamp Module is that the majority of our code examples are written around the BASIC Stamp 2 which is the most popular and has been around the longest.· Newcomers to the BASIC Stamp often have difficulty getting these examples working not knowing that the timing is different among different Stamp Models.· Conditional compilation may help users familiar with the BASIC Stamp but for a beginner knowing how to insert the proper constants for different commands/Stamps can be frustrating.

·· I would suggest that perhaps starting out with something like the Discovery Kit would be a good way to get familiar with the BASIC Stamp 2 and how to program and interface to it.· And then upgrade the Stamp Module later if need be.· You can always add the LCD and keypad at any time.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com

Mike Green

That's very true about newcomers potentially having problems using the examples. I have stumbled over the problem of different timing constants for different Stamp processors myself although the conditional compilation feature has helped a lot. My main reason for suggesting the BS2p series is that they have built-in support for parallel LCDs. You can certainly interface easily to them using any of the Stamps, but it's easier with the built-in statements. I have also found that projects tend to expand and picking processors with more speed, memory, and other features that may not be needed initially make things easier later as long as the costs of the additional capability are small. That said, really any of the Stamp 2 processors should be more than adequate for the task and the Discovery Kit is a good way to get started.

The main Nuts & Volts article on interfacing to LCDs is #97 in Volume #4 <http://www.parallax.com/dl/docs/cols/nv/vol4/col/nv97.pdf>, but there's a "treasure trove" of examples and advice in the other articles and texts on the Parallax website.

Mike

Mitch

Mike and Chris:

Thanks for the speedy replies. Man you guys are fast, it's hard to keep up <g>...

I have the learning kit from my local Radioshack and have been dinking around with that. I have done the exercises and taken off and built som prop contollers for our halloween display; the last prototype included IR remote control. I want to expand that one to use the Ultrasound modules to watch for people coming and going and trigger events accordingly. This has been a blast for a programmer geek!

Also being a hardware geek, the extra oomph of the 'p' series BS2 is attractive. At the same time, the Project Manager side of me says I get the feeling that ~4k instructions per sec. may be adequate as·may ~500 instructions in 2k memory; especially in light of the fact that I'm looking at offloading most of the keypad processing to the decoder module. The 4x20 LCD is a serial display that looks pretty straight forward.

Just my thoughts ... I'll be the first to acknowledge that I'm just a beginner on these matters though <g>.

Thanks for your help, any further insights and input are appreciated. I will look at the NV articles too; Jon's column is why I subscribe to that magazine <g>.

Mitch

Mike Green

One other suggestion ... You really have two tasks here: 1)The user interface (display formatting and control and the keypad entry) and 2) The algorithm for change-making. I suggest working on the separately at first. Stamp 2 programs can communicate with the PC over the serial port used for programming using the DEBUG and DEBUGIN statements. Use those instead of the keypad/LCD initially until you get the change-making algorithm working properly, then work on the keypad/LCD hardware and software, then combine them.

Mike

Mitch

Mike:

You are right on mark, in fact I was going to start playing around this weekend even before investing in the hardware. Although the language is BASIC, you can still "modularize" things·by incorporating subroutines; which really facilitates a quasi-modular style of·development.

I can develop all of the support·subroutines for input processing, formatting and calculations, etc. on my WAM board.

Ah, the fun of new toys and projects <g>.

Thanks for the ideas,
Mitch

Mitch

Mike, Chris or any others:



Here's what I believe to ba a good "parts list":

Board: Super Carrier (27130)
Stamp Module: BS2e-IC (BS2E-IC) Gives me extra EEPROM and program space. Seems like a good compromise.
Display: Parallax 4x20 LCD (Backlit) (27979)
Display ext. Cable: 14" with header (805-00002,451-00303)
Keypad: 4x4 Matrix Keypad (27944)
Keypad Custom Cable: (27943)
Decoder: Memkey decoder (27963)



Need to find:

Project box/case with battery compartment.
5 pin, right angle header (female).



Has anyone mounted the Decoder Module on the Super Carrier board with a right angle header? This would make it almost like a piggyback arrangement to save space. What about heat build-up (if there is any between the Decoder and Super Carrier)? Will there be enough clearance between the Super Carrier and the Decoder? Will there be enough clearance to connect the Custom Cable (for the keypad)?

Thanks for your input along the way. Now off to start the "Operating System"..

Mitch

Chris Savage

Mitch,

·· If you need to save space you can always use a single chip solution as well.· In this case either an SX Chip programmed as a Keypad Decoder or a chip such as the 74C922 or the EDE1144.· If you solder a right-angle header onto the Memkey board and there's a problem you will be without a warranty.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com

Mitch

Chris:

I thought about the 74C922 after reading one of the AppNotes. Which one is faster, more reliable, more straight forward to program; the 74C922 or the EDE1144?

Out of curiosity, how do the Memkey users interface it with the Parallax boards? I was actually thinking of the header socket being soldered onto the Super Carrier Board and then plugging the existing pins of the Memkey into the socket (no modification necessary???).

Thanks for your help and ideas. I'm off to look at the other 2 single chip encoders.

Thanks,
Mitch

Mike Green

A good source for ICs, headers, etc. is Digikey <http://www.digikey.com>. Jameco and Mouser are also good, but Digikey has a larger selection of parts and all of them allow you to order from their on-line catalogs over the Internet. I've personally used Digikey and Jameco for several years and have been very happy with their service, prices, etc. Jameco does not have female headers, but Digikey does (I just got some for a project from them).

Mike

Mike Green

I would not worry about heat with the Memkey decoder or even most of the peripherals sold by Parallax. The only ones that would handle enough power for that to be any concern would be stepper and dc motor controllers. Servo controllers just handle a low level control signal.

Mike

Chris Savage

Mitch,

·· Each person has a different application and many use different boards or people like me will often make a custom PCB.· So that varies.· You really need to examine the choices and pick the best one for your application.· Good luck.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com