LDR Programming Help!

jmathews8

I've been working on a project that has been going well until I got the programming portion of it. I'm making a set of blinds that open when light strikes the LDR and then closes when a decreased amount hits it. The only problem is that I don't know how to get started with that. The programming knowledge of our class doesn't encompass this much stuff. How do I get the LDR to tell the Servo motor to begin turning the blinds open?

prof_braino

My advice is that you need to address the PLANNING before you think about coding.

This is two separate problems:
1) reading the sensor.
2) controlling the actuator.

We need to know something about the LDR (such as a link to its datasheet). Then you can start to ask about getting reading from it.
Then we need to know a little something about the servo, such as is it a stock hobby servo, and which one.

Once you determine how to accomplish steps 1 & 2, then step three, writing code to that brings these together as your application, is a piece of cake.

John Abshier

Chapter 7, Measuring Light, of What's a Microcontroller http://www.parallax.com/Portals/0/Downloads/docs/prod/edu/28123-WAM-v3.0.pdf may help. It also covers controlling hobby servos.

John Abshier

jmathews8

Alright, here's my code so far. The only problem is that whenever the LDR stays in the darkness, it keeps turning counter-clockwise.

' {$STAMP BS2sx}
' {$PBASIC 2.5}
LdrValue VAR Byte
PIN6 PIN 6 'ldrsensor
pin12 PIN 12 'servo
pin15 PIN 15 'led
Baud CON 396 '9600 Baud
counter VAR Word
OUTPUT pin12
LOW PIN12
'the lightness has levels from 0 TO 255 AND I choose 150 AND beyond TO turn LED ON
LdrValue = 0
DO
here: SERIN pin6, Baud, [LdrValue]
'DEBUG CLS, DEC LdrValue, CR
IF LdrValue >= 250 THEN
FOR counter =1 TO 100
PULSOUT pin12, 2125
PAUSE 20
NEXT
FOR counter = 1 TO 100
PULSOUT pin12, 1875
HIGH 15
PAUSE 20
NEXT
ENDIF
IF LdrValue <= 250 THEN
FOR counter =1 TO 100
PULSOUT pin12, 1625
LOW 15
PAUSE 20
NEXT
FOR counter =1 TO 100
PULSOUT pin12, 1875
NEXT
ENDIF
LOOP

Any assistance would be greatly appreciated.

Mike Green

You need to follow the advice you've been given. First you write a program that uses the DEBUG statement to tell you what the LDR values are and verify that the program (and the LDR) behave as expected. Then you modify that program to use the DEBUG statement instead of a servo to tell you what the servo would do depending on the light level. You write another program that just moves the servo to one position based on a value from a DEBUGIN statement that tells it whether to open or close. Once you've gotten that far, you should be able to combine the two programs for your finished project.

You might also use the [ code ] and [ /code ] tags along with indenting to show the structure of your program, namely which statements are under control of which IF / THEN and FOR / NEXT statements. Comments also can help describe a program's functioning to another person and often help you in your own understanding of the program and its errors.

kwinn

You also need a way to sense when the blinds are fully opened and fully closed so you can stop the motor at that point. This is usually done with one or two microswitches or optical sensors.