Some help for a beginner

Judith · 2007-12-26 00:08

Hey, I'm pretty new to microcontrollers, so I was wondering whether anyone could help me with what I'm trying to make. The overall goal is to make a vehicle that travels a certain distance and then stops when it reaches that distance. I want to hook up a switch to one of the inputs on the BASIC stamp--when the switch closes the circuit, the BASIC stamp saves it to a variable. So say I press the switch 5 times, the variable will say 5. Then, an output switch will send out a signal to a servo, and the number of times the signal is sent out will be the number of times the switch was pressed, basically (I'll have to multiply the number of times its looped by a certain number so that it travels the distance I want it to). Once its repeated this many times, the motor will engage in reverse, braking the vehicle. This is the code I've written so far:

DIRS=%0000000000000011
SwitchIn VAR BYTE
TotalSwitch VAR WORD
PULSIN 4, SwitchIn
DO
IF SwitchIn=1 THEN TotalSwitch = TotalSwich+1
LOOP
i VAR WORD
i = TotalSwitch
DO
PULSOUT 15, 300
PAUSE 10
LOOP
i=20
DO
PULSOUT 15, -300
PAUSE 10
LOOP
END

I have a couple of questions--first, I know that the BASIC stamp will read the PULSIN command for every 2 microseconds that power is run through it--so say I press the switch for 8 microseconds, will that create 4 separate instances of PULSIN that will be stored in the variable? Also, I'm pretty sure the code is wrong in lots of places...this is my first time coding a microcontroller :P...any suggestions on how to fix the places I've screwed up in?

Unsoundcode · 2007-12-26 01:03

For the servo values of a BS2 they should fall in the range 500-1000 (-300 is not valid ) with 750 being a stopped or neutral position. PULSOUT 15,600 will drive the motor one way and PULSOUT 15,900 will drive it the other way.

Look at the BUTTON instruction for the switch input.

Look at the FOR...NEXT instruction to cycle the number of times the button was pressed

When the code exits the FOR ... NEXT loop then stop the motor with PULSOUT 15,750

Jeff T

Judith · 2007-12-26 03:01

ah ok, thanks a lot! So do you think this will work? I have 2 buttons--one to actually say how long I want it to loop for, then another one to tell it when I've stopped enterint input, because I'm not sure how else I would make it jump to the next bit of code.


DIRS=%0000010000000011 'all input except p15 and p16

gWorkspace1 VAR BYTE
gButtonCounter VAR NIB
gWorkspace2 VAR BYTE
repeat VAR WORD
i VAR WORD
DO
BUTTON1:
LOOP:
    'BUTTON Pin, DownState, Delay, Rate, Workspace, TargetState, Address
    BUTTON 4, 1, 255, 0, gWorkspace1, 1, press1

noPress1:
    DEBUG "no, not pressed. ", DEC ? gButtonCounter
    GOTO BUTTON1

press1:

    gButtonCounter = gButtonCounter + 1
    DEBUG "yes, pressed", DEC ? gButtonCounter

    
    GOTO BUTTON1

DO
LOOP:
    BUTTON 5, 1, 255, 0, gWorkspace2, 1, press2

press2:
    DEBUG "stop counting", DEC ? gButtonCounter
    GOTO main

main:
DO
repeata:
LOOP
gButtonCounter=i
    PULSOUT 15, 600
    PAUSE 10
    i=i-1
    IF i>0 THEN GOTO repeata
    IF i=0 THEN GOTO repeatb
DO
repeatb:
LOOP
    PULSOUT 15, 900
    PAUSE 10
    PULSOUT 15, 900
    PAUSE 10
    PULSOUT 15, 900
    PAUSE 10
    PULSOUT 15, 750
    PAUSE 10
END

Unsoundcode · 2007-12-26 03:44

Heres an adaptation of the button instruction in the IDE help file

Time_out CON 500
Btn············ PIN···· 0
btnWrk········· VAR···· Byte
Idx VAR Word
Pressed VAR Byte
Main:

DO WHILE Idx<Time_out
· PAUSE 5
· BUTTON Btn, 0, 255, 255, btnWrk, 0, No_Press
· DEBUG "*"
· Pressed=Pressed+1
· Idx=0
· No_Press:
· Idx=Idx+1
LOOP
DEBUG CR,"Timed out" ," ",? Pressed
END

Once you cease pressing the button the variable Time_out controls how long it is before the program continues. Run this as stand alone code and play with the settings.

Jeff T.

Judith · 2008-01-06 16:05

Thanks a lot for the help. I have managed to test the button and servo circuits separately and everything works fine, but when I star the program, it loops endlessly for some reason, even though I only want it to loop once.
Here's the code:

Btn VAR Byte
Time VAR Word
Btn = 0
Counter VAR Word
DO

DEBUG ? IN4

IF (IN4 = 1) THEN
Btn = Btn+1
PAUSE 250
DEBUG ? Btn
ELSE
PAUSE 250
Time=Time+1
ENDIF

LOOP UNTIL Time = 200
DEBUG "Starting Servo"

FOR Counter = 1 TO (BTN * 10)
PULSOUT 14, 1000
PAUSE 20
NEXT

DEBUG "Braking", CR
FOR Counter = 1 TO 25
PULSOUT 14, 500
PAUSE 20
NEXT

DEBUG "DONE", CR

END

when I run it, it just debugs IN4 and Btn, and doesn't start the servo nor timeout...

Unsoundcode · 2008-01-06 17:35

Hi Judith, from what you say IN4 is always 1. This is probably because of the way the button is connected to the Stamp. I am assuming the button has normally open contacts, it should be wired this way ,

VDD to one side of the button

on the other side of the button connect a 220 ohm resistor

connect the other end of the 220 ohm resistor to P4

now take a 10K ohm resistor and connect one end to P4

connect the other end of the 10K resistor to VSS

try your program again and see how it responds

Jeff T.

Bruce Bates · 2008-01-06 17:45

Judith -

Indeed if IN4 always equals 1, the program will loop forever since the variable TIME will never be incremented, and thus will never reach the LOOP UNTIL value of 200. You never mention what the DEBUG values are for IN4 and Btn. It might be interesting to put in a DEBUG statement for TIME as well.

You don't mention what is attached to pin port 4, nor how it is hooked up (circuitry).

I suppose it's fair to presume that "Starting Servo" is never displayed?

You have also not indicated to us, nor to the PBASIC compiler which PBASIC Stamp you are using?

Regards,

Bruce Bates

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Judith · 2008-01-06 20:42

Bruce and Jeff,

Sorry, in the original code I have

' {$STAMP BS2}
' {$PBASIC 2.5}

at the beginning, I just forgot to paste it into my post.

I have a switch connected to pin 4 through a 200 ohm resistor, with a 10k pulldown resistor. The debug values for IN4 indicate that the button circuit is working--it's 0 when it's not pressed, and 1 when it is. The Btn values also seem to be working, as they store the number of times I press the button. When I put in a DEBUG statement for TIME, it went up to 200, then displayed "Starting Servo" and restarted. Also, the Btn variable resets itself. However, the servo itself (which is correctly connected to pin 14, I checked with a test program and it worked fine) never turns on. That's what makes me think I wrote the loop code wrong...

Judith

Post Edited (Judith) : 1/6/2008 9:04:55 PM GMT

Bruce Bates · 2008-01-06 22:14

Judith -

If you are powering the servo directly from the Stamp's power supply, it may be causing a brown-out condition, and the Stamp itself is resetting. You can check that by adding the following DEBUG statement right at the beginning of your program, before any looping takes place: DEBUG "STARTING". "STARTING" should appear once and ONLY once during any iteration of the program. If it appears more than once, the Stamp is being RESET.

Regards,

Bruce Bates

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Judith · 2008-01-06 23:36

Bruce,
Thanks! That seems to have been the problem, I gave the servo its own 9V power supply and it's working fine [noparse]:)[/noparse]

Thanks again,
Judith

Bruce Bates · 2008-01-06 23:49

Judith -

Using 9 volts DC for a servo is a bit high. Generally one doesn't supply them with more than 6-7.5 volts DC.

Regards,

Bruce Bates

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Some help for a beginner

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