More outputs on a BS1 rev. D

akudaikon

I've had a BS1 rev. D for a couple years now and could never figure out what do with it. Now I have an idea for a project over the summer, but I've run into an issue. I have a limited knowledge of electronics right now, so i'm trying to come up with ways from what I know to overcome it. The basic stamp only has 8 input/output pins, but I need to be able to independantly control 27 different LEDs while leaving 1 or 2 pins open for inputs. I was thinking of using a demultiplexer, but I cannot find any 1:32 demultiplexers to do this. Does anyone have any ideas or solutions to this problem? I'm sure there is a simple solution to this.

Thanks in advance for the help!

Jon Williams

You could dasiy-chain four 74HC595's to get 32 outputs. Since there is no SHIFTOUT instruction you'll have to do it with code.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

SSteve

You could use four 74HC595 shift registers with three pins. Download the StampWorks manual and check out experiment #23.

Edit: I guess Jon and I were typing at the same time.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
OS-X: because making Unix user-friendly was easier than debugging Windows

akudaikon

Thanks for the quick replies!! I just looked at the stampworks manual and it gives a good explaination of how to do it.

Thanks again for the help!!

Jon Williams

Here's a·bit of code for sending data to a '595 with the BS1.· The byte to output is put in 'temp' and then the SHIFT_OUT subroutine is called:

SYMBOL· SData·· = Pin0················· ' 74HC595 serial data· (14)
SYMBOL· Clock·· = 1···················· ' 74HC595 shift clock· (11)
SYMBOL· Latch·· = 2···················· ' 74HC595 output latch (12)

SYMBOL· temp··· = B0··················· ' work variable for LCD routines
SYMBOL· shift·· = B4··················· ' loop counter for SOut

SHIFT_OUT:·····
· FOR shift = 1 TO 8··················· ' shift 8 bits
··· SData = Bit7······················· ' MSB first
··· PULSOUT Clock, 1··················· ' clock the bit
··· temp = temp * 2···················· ' get next bit
· NEXT
· PULSOUT Latch, 1
· RETURN

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

akudaikon

Thanks for the code! I didn't realize that BS1's didn't support SHIFTOUT so that will really help me out. I have another programming question for you though. I'm trying to come up with a way to generate unique random numbers within a range of numbers. For example, 4 unique random numbers within 1 to 10. The BS1 is so limited and i've been racking my brain for a long time now trying to think of a way to do it. Is there any solution or is it even possible to do?

Thanks a lot again for the help!

akudaikon

Nevermind. I thought of a way to do it.

Jon Williams

Here's how I usually do it -- let's say you want a random value between 5 and 30.· The code is:

· target = rndValue // 26 + 5

The divisor for modulus is the max value minus the min value plus one (30 - 5 + 1 = 26).· The reason for this is that the modulus operator always returns a value between zero and the divisor-1, so in the code above the modulus portion would always return a value between 0 and 25.· Then we add the minimum value to bias the output to it.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax