Using Photocell to detect winner of race

mechjo16 · 2015-03-26 05:13

Hello all,

I am new to using the BS2. I am working with my son and we are building a hot wheels track. There will be two separate tracks. Down hill drag strips if you will. What I am looking to accomplish is for a led it come on when the winning car blocks the light from the photo resistor. However, I do not what the led to come on when the losing car blocks its photo resistor (this is the part that has me stumped both cars get a light coming on).

Thank you in advance.

John

Updated 4-2-2015
Almost there. Got the phototransistors working and learned about subroutines. I'm just having problems with the subroutines executing properly. Any help would be appreciated.

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

'Declare variables
Counter VAR Word 'Defines variable as word

PAUSE 1000 'Initial 1 second pause
DEBUG "Program Running!", CR 'Display "Program Running"

'

'Switch control
DO
DEBUG ? IN0
PAUSE 20
IF (IN0 = 1) THEN

'

'Ready set go lights
'FOR counter = 1 TO 1 'Cycle code 1 time

'DEBUG ? counter
HIGH 15 'Red LED on
LOW 14 'Green LED off
LOW 13 'Yellow LED off
PAUSE 2500

FOR counter = 1 TO 3 'Flase Yellow LED 3 times
DEBUG ? counter
LOW 15 'Red LED off
LOW 14 'Green LED off
HIGH 13 'Yellow LED on.
PAUSE 1500
LOW 13 'Blink yellow light 3 times
PAUSE 500
NEXT

HIGH 14 'Green LED on
LOW 15 'Red LED off
LOW 13 'Yellow LED off
PAUSE 2500 'Green LED on for 2.5 seconds
'LOW 14 'Green LED off
'NEXT
'

' Servo Action

FOR counter = 1 TO 50 ' release cars
PULSOUT 12, 1200
PAUSE 20
DEBUG "Release cars", CR

NEXT
PAUSE 1000 ' set car release for 1 second
LOW 14 ' Turn green LED off
FOR counter = 1 TO 50 ' set car release back to hold position
PULSOUT 12, 750
PAUSE 20
DEBUG "Reset car release", CR
NEXT
'

'Which car won
IF IN6 = 0 THEN
GOSUB car1win
DEBUG "back from car1sub"

ELSEIF IN4 = 0 THEN
GOSUB car2win
DEBUG "back from car2sub"

ENDIF

'

'Subroutines
Car1win:

DEBUG ? IN6
PAUSE 20

IF (IN6 = 0) THEN

' FOR counter = 1 TO 1 'Cycle code 1 time

' DEBUG ? counter
HIGH 9
PAUSE 5000
LOW 9
' NEXT
' ELSE
PAUSE 20
ENDIF
RETURN

'

Car2win:

DEBUG ? IN4
PAUSE 20

IF (IN4 = 0) THEN

' FOR counter = 1 TO 1 'Cycle code 1 time

' DEBUG ? counter
HIGH 3
PAUSE 5000
LOW 3
' NEXT
' ELSE
PAUSE 20
ENDIF
RETURN
'

'Close the switches if statement
ELSE
PAUSE 20
ENDIF

LOOP

Mike Green · 2015-03-26 07:46

I'm a little confused about what you want to do. How many LEDs do you have and what do you want each one to show?

erco · 2015-03-26 07:57

Make a loop which rapidly samples both sensors, exiting the loop when either senses a car. Then turn on the appropriate LED.

BTW, photocells are slow. RCtime can be slow if component values are wrong. These could limit your ability to properly sense when 2 cars are very close. I'd recommend using two phototransistors, each with a series ~1 Meg resistor. That makes a pair of voltage dividers which can be read instantly as either high or low, much faster than photocells and RCtime.

mechjo16 · 2015-03-26 08:03

Mike Green wrote: »

I'm a little confused about what you want to do. How many LEDs do you have and what do you want each one to show?

At the finish line I have a photo resistor on each track to detect the winner. When the photo resistor light is blocked I want the LED to come on...Above the track I have a led over each lane. So 2 LED's Total. Right now as both cars finish the race, as the photo resistor light is blocked, both LED's come on.

Let's say my son's car finishes first. I do not want my LED to come on. I want my light to stay off so my son can see he won...... So basically, only the winner gets the light.

Mike Green · 2015-03-26 10:17

Erco's suggestion would work. Another idea is to have a variable (call it WINNER) that's initialized to zero. You have a loop in your program that checks one photocell, then the other. If a photocell is blocked, you check WINNER. If WINNER = 0 then you set WINNER to the photocell number (1 or 2) and light up the corresponding LED. You can either reset the Stamp for each new race or have a pushbutton that's tested each time through the loop. If the pushbutton is pressed, the LEDs get turned off and WINNER is reset to zero. Here's a pseudo-code version:

DO
  <measure photocell1 resistance>
  <measure photocell2 resistance>
  IF <pushbutton pressed> THEN
    LOW LED1 : LOW LED2 : WINNER = 0
  ELSEIF <photocell1 resistance < threshold> AND WINNER = 0 THEN
    WINNER = 1 : HIGH LED1
  ELSEIF <photocell2 resistance < threshold> AND WINNER = 0 THEN
    WINNER = 2 : HIGH LED2
  ENDIF
LOOP

mechjo16 · 2015-03-26 11:03

Thanks for the tips guys. I will play with it some more this weekend. I appreciate you time experience.

mechjo16 · 2015-03-27 07:57

If it helps I tried to do a flow chart of what I am trying to accomplish. See below.

I thought I could get the winning LED to come on, guess that is not working either.

So far I have been able to go through the "ready, set, go" light cycle and get the servo to release the cars.

HW Race Flow chart.pdf

kwinn · 2015-03-27 08:54

A BS2 seems to be a bit of overkill for this. You should be able to do this with a 556 (dual 555) timer when there are only two sensors.

mechjo16 · 2015-03-27 09:04

I'm not familiar with the 555 timer.

I just figured I'd buy the BS2 kit, this way I could keep my sons attention if it was incorporated with things he likes like lego's and cars while at the same time learning a new useful skill.

Publison · 2015-03-27 09:11

mechjo16 wrote: »

I'm not familiar with the 555 timer.

I just figured I'd buy the BS2 kit, this way I could keep my sons attention if it was incorporated with things he likes like lego's and cars while at the same time learning a new useful skill.

That's a perfectly valid concern, using the BS2. It is a great MicroController for young people.

That said, I am going to move this to the BS2 Forums where it will get more exposure.

Domanik · 2015-03-27 09:57

mechjo16 wrote: »

I'm not familiar with the 555 timer.

I just figured I'd buy the BS2 kit, this way I could keep my sons attention if it was incorporated with things he likes like lego's and cars while at the same time learning a new useful skill.

Sounds like loads of fun. You could do all sorts of things with your son while creating interactive things with the BS2. For example:
1) A series of red LEDs on a narrow vertical stand that down counts to start the race.
2) A speaker / buzzer to start when the last LED flashes
3) A push button to reset the finish LEDs

Kids love things that have cause and effect- push a button and get a sound or flashing light; like sound effects from a dragster race when a button is pushed. Legos are great for making Hot Wheels bridges or ramps to jump and crash. It would be great if your son used the BS2 to modify the cause & effect he gets.
Just thinking...

mechjo16 · 2015-03-27 10:12

Domanik wrote: »

Sounds like loads of fun. You could do all sorts of things with your son while creating interactive things with the BS2. For example:
1) A series of red LEDs on a narrow vertical stand that down counts to start the race.
2) A speaker / buzzer to start when the last LED flashes
3) A push button to reset the finish LEDs

Kids love things that have cause and effect- push a button and get a sound or flashing light; like sound effects from a dragster race when a button is pushed. Legos are great for making Hot Wheels bridges or ramps to jump and crash. It would be great if your son used the BS2 to modify the cause & effect he gets.
Just thinking...

Were still crawling my friend. I'm still trying to get my head wrapped around photo sensors. lol

The BS2 does look like a lot of fun once you figure it out. Some of the things I've seen on-line blow my mind.....All I get is awww dad can we do this, can we do that...sure son (as bullets are sweating from my head).

Genetix · 2015-03-27 14:49

The BS2 is very easy to use so it's perfect for a newcomer.
What's a Microcontroller? was written for someone without electronics or programming experience so it's highly recommended to start with that is you haven't already.
https://www.parallax.com/product/28152

What did you use to make that nice flow chart?

mechjo16 · 2015-03-27 15:16

Genetix wrote: »

The BS2 is very easy to use so it's perfect for a newcomer.
What's a Microcontroller? was written for someone without electronics or programming experience so it's highly recommended to start with that is you haven't already.
https://www.parallax.com/product/28152

What did you use to make that nice flow chart?

Yeah the book came with the kit... just having a hard time with the phototransistor part...

I did the flow chart in MS Visio. I'm not sure if the flow chart is right. I just captured what I am trying to do.

Domanik · 2015-03-27 16:18

mechjo16 wrote: »

I did the flow chart in MS Visio. I'm not sure if the flow chart is right. I just captured what I am trying to do.

RE Flowchart: The "Do Nothing"s needs to loop back to "Which car won?" until the decision block goes YES then fall thru and go back to start. As it's written you'll test for a winner then fall thru to END and stop.

Mike Green's code looks pretty good.

How many functions work? Read start switch, cycle LED, servo on/off, photo detection = TRUE/FALSE? It's always good to know what parts are solid.

mechjo16 · 2015-03-28 11:42

Got Phototransistors operating, having trouble with subroutines executing properly.

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

'Declare variables
Counter VAR Word 'Defines variable as word

PAUSE 1000 'Initial 1 second pause
DEBUG "Program Running!", CR 'Display "Program Running"

'

'Switch control
DO
DEBUG ? IN0
PAUSE 20
IF (IN0 = 1) THEN

'

'Ready set go lights
'FOR counter = 1 TO 1 'Cycle code 1 time

'DEBUG ? counter
HIGH 15 'Red LED on
LOW 14 'Green LED off
LOW 13 'Yellow LED off
PAUSE 2500

FOR counter = 1 TO 3 'Flase Yellow LED 3 times
DEBUG ? counter
LOW 15 'Red LED off
LOW 14 'Green LED off
HIGH 13 'Yellow LED on.
PAUSE 1500
LOW 13 'Blink yellow light 3 times
PAUSE 500
NEXT

HIGH 14 'Green LED on
LOW 15 'Red LED off
LOW 13 'Yellow LED off
PAUSE 2500 'Green LED on for 2.5 seconds
'LOW 14 'Green LED off
'NEXT
'

' Servo Action

FOR counter = 1 TO 50 ' release cars
PULSOUT 12, 1200
PAUSE 20
DEBUG "Release cars", CR

NEXT
PAUSE 1000 ' set car release for 1 second
LOW 14 ' Turn green LED off
FOR counter = 1 TO 50 ' set car release back to hold position
PULSOUT 12, 750
PAUSE 20
DEBUG "Reset car release", CR
NEXT
'

'Which car won
IF IN6 = 0 THEN
GOSUB car1win
DEBUG "back from car1sub"

ELSEIF IN4 = 0 THEN
GOSUB car2win
DEBUG "back from car2sub"

ENDIF

'

'Subroutines
Car1win:

DEBUG ? IN6
PAUSE 20

IF (IN6 = 0) THEN

' FOR counter = 1 TO 1 'Cycle code 1 time

' DEBUG ? counter
HIGH 9
PAUSE 5000
LOW 9
' NEXT
' ELSE
PAUSE 20
ENDIF
RETURN

'

Car2win:

DEBUG ? IN4
PAUSE 20

IF (IN4 = 0) THEN

' FOR counter = 1 TO 1 'Cycle code 1 time

' DEBUG ? counter
HIGH 3
PAUSE 5000
LOW 3
' NEXT
' ELSE
PAUSE 20
ENDIF
RETURN
'

'Close the swithes if statement
ELSE
PAUSE 20
ENDIF

LOOP

Beau Schwabe · 2015-03-28 14:26

As mentioned earlier the BS2 is really overkill for this application ... Also mentioned was the learning perspective and future gained skill set. While the learning advantage for a future skill could be argued, the art of analog circuit design is also a valuable skill set that can also be applied as well ... Here is a circuit design that uses a dual Op-Amp, a handful of resistors and a couple of transistors to create what is called a "Wheat-stone bridge" or balance bridge. When the balance of the bridge is thrown out of balance, it latches to one side or the other preventing the other sensor from flipping it to the other side. To "reset" the circuit you need to cycle the power. This circuit has the option of using a Photo transistor or Photo resistor, however you shouldn't mix or match the two.

http://bscircuitdesigns.com/Parallax/GAME.JPG

mechjo16 · 2015-03-28 18:00

Mike Green wrote: »
Erco's suggestion would work. Another idea is to have a variable (call it WINNER) that's initialized to zero. You have a loop in your program that checks one photocell, then the other. If a photocell is blocked, you check WINNER. If WINNER = 0 then you set WINNER to the photocell number (1 or 2) and light up the corresponding LED. You can either reset the Stamp for each new race or have a pushbutton that's tested each time through the loop. If the pushbutton is pressed, the LEDs get turned off and WINNER is reset to zero. Here's a pseudo-code version:
DO
  <measure photocell1 resistance>
  <measure photocell2 resistance>
  IF <pushbutton pressed> THEN
    LOW LED1 : LOW LED2 : WINNER = 0
  ELSEIF <photocell1 resistance < threshold> AND WINNER = 0 THEN
    WINNER = 1 : HIGH LED1
  ELSEIF <photocell2 resistance < threshold> AND WINNER = 0 THEN
    WINNER = 2 : HIGH LED2
  ENDIF
LOOP

I went and picked up some Phototransistors.... How do I incorporate this code into mine (see above), I know it needs to go after the servo action.... Also, how do I stay in this part of the code until a winner crossed the line before it goes back into looking for the reset switch input again?

erco · 2015-03-29 08:18

One step at a time, moy drug! Test your ptx (phototransistors) with a series 1 megohm resistor in a voltage divider arrangement. Put 5V across the combo (polarity matters, unlike a photocell) and use a multimeter to check the voltage at the ptx/resistor junction as you shade the ptx from ambient light, pointing the ptx up in realistic indoor lighting conditions. You want a big voltage change from light to dark, with extremes on either side of 1.4V. The Stamp reads a pin under 1.4V as low, above 1.4V as high, perfect for using an IF check in your program to read the sensor.

Domanik · 2015-03-29 09:18

mechjo16 wrote: »

how do I stay in this part of the code until a winner crossed the line before it goes back into looking for the reset switch input again?

Generally you want to loop on a set of instructions and check, at the end, to see if something happened to tell you it's time to move. "DO LOOP" until one LED is on. The LED will be on when a car crosses the finish line. Somehow you define the block of code with end and start key statements. Like "DO --- LOOP", "WHILE (Condition) --- END WHILE". This is different than a FOR loop that increments a variable until it's reached its max count then falls through or an IF that executes some code if true one time.

Phototransistors: Do you have a part number from the manufacture? Manufactures provide "datasheets" that describe their parts specific operating parameters and in some cases provide an example application circuit. Everything Sir Erco said is spot on to come up with a working circuit without a datasheet. A phototransistor is like a 1 meg pot that changes resistance as the light changes. It goes down in with brighter light and up as it gets dark. If you google "Phototransistors" there are plenty of images of circuits with just the two parts.

erco · 2015-03-29 11:05

Good ambient lighting is key to using phototransistors successfully. From my experience, a 1-megohm series resistor yields good results in average indoor conditions, but will not work outdoors or in dim light. Worst case (for oddball indoor lighting conditions), you may have to add an IR LED shining at the phototransistor, creating a break-beam detector.

Using DC light level sensors outdoors reliably is very difficult. Sunlight gets everywhere.

mechjo16 · 2015-04-02 18:30

Updated the code to where I am at (see post 1) I'm stuck on executing subroutines properly. Any help would be appreciated.

erco · 2015-04-02 19:46

Good effort, you were very close. I'd say subroutines are not needed here. Try the attached program and see if it's any better.

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

 'Declare variables
 Counter VAR Word ' Defines variable as word

 PAUSE 1000 'Initial 1 second pause
 DEBUG "Program Running!", CR 'Display "Program Running"

 '-------------------------------------------------------------------

 'Ready set go lights
 main: HIGH 15 'Red LED on
 LOW 14 'Green LED off
 LOW 13 'Yellow LED off
 PAUSE 2500

 FOR counter = 1 TO 3 'Flash Yellow LED 3 times
 DEBUG ? counter
 LOW 15 'Red LED off
 LOW 14 'Green LED off
 HIGH 13 'Yellow LED on.
 PAUSE 1500
 LOW 13 'Blink yellow light 3 times
 PAUSE 500
 NEXT

 HIGH 14 'Green LED on
 LOW 15 'Red LED off
 LOW 13 'Yellow LED off
 PAUSE 2500 'Green LED on for 2.5 seconds
 'LOW 14 'Green LED off
 'NEXT
 '------------------------------------------------------------

 ' Servo Action
 DEBUG "Release cars", CR
 FOR counter = 1 TO 50 ' release cars
 PULSOUT 12, 1200
 PAUSE 20
 NEXT
 PAUSE 1000 ' set car release for 1 second
 LOW 14 ' Turn green LED off

 DEBUG "Reset car release", CR
 FOR counter = 1 TO 50 ' set car release back to hold position
 PULSOUT 12, 750
 PAUSE 20
 NEXT
 '--------------------------------------------------------------

 DO                     'scan both finish sensors rapidly in loop
 IF IN6=0 THEN Car1win
 IF IN4=0 THEN Car2win
 LOOP

 '--------------------------------------------------------------
 Car1win:

 DEBUG "Car 1 Wins!", CR

 HIGH 9       'Lane 1 LED ON FOR 5 seconds
 PAUSE 5000
 LOW 9        'LED off
 GOTO main


 '----------------------------------------------------------------
 Car2win:

 DEBUG "Car 2 Wins", CR

 HIGH 3        'Lane 2 LED ON FOR 5 seconds
 PAUSE 5000
 LOW 3         'LED off
 GOTO main

mechjo16 · 2015-04-03 06:23

That works! Thanks everyone for working with me.

erco · 2015-04-03 14:22

HTH. Be sure to post a video of your finished project with your son racing! I designed Hot Wheels track sets for Mattel for 30 years.

Using Photocell to detect winner of race

Comments