Hot Wheels Car Photogate

Measure how fast your Hot Wheels car moves at different points on your track or use it to tell how fast your race was.

May 30, 2019

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14 respects

cars

timer

photogate

Components and supplies

Photo transistor light sensor

Arduino UNO

Through Hole Resistor, 200 kohm

Through Hole Resistor, 2k ohm

High Brightness LED, White

Tools and machines

3D Printer (generic)

Solder Wire, Lead Free

Soldering iron (generic)

Project description

Code

Single LED Photogate

arduino

Single photogate code for measuring of the speed of a single Hot Wheels car. The code allows the photogate to work in either direction.

1/* PhototransistorVoltage Hot Wheels Timer
2 * Power phototransistor  with 5v and GND
3 * Connect the phototransistors yellow wire into A1 
4 * Optional:  Use a piezo buzzer connected to pin 4 and GND.
5 */
6
7const int buzzerPin  = 4;  // other end of buzzer connected to GND
8float threshold = 0.25;    // voltage  where phototransistor shows car is in the way
9const int interval = 5;  // accuracy  of timer in milliseconds
10
11void setup()                                 //  Built-in initialization block
12{
13  Serial.begin(9600);                        //  Set data rate to 9600 bps
14}
15
16float v1, timerCount;
17boolean waitFor2ndTrigger;
18
19void  loop() {
20  tone(buzzerPin, 440*6, 50);                   // Sound "ready"
21  timerCount = 0;
22  waitFor2ndTrigger = true;
23  v1 = volts(A1);                                //  measure voltage from phototransister in A1
24  tone(buzzerPin, 880, 150);                     //  Sound for start of waiting for trigger
25  Serial.println("Waiting for trigger...");      // wait for  phototransistor to be dimmed
26  while (v1 > threshold) { 
27   delay(interval);                   // otherwise it's too fast to notice button  press ((when one is used)
28   v1 = volts(A1);                    // measure voltage  from phototransister in A1
29    }
30  Serial.print("Started...");                    //  Display "Start"
31  
32  while (waitFor2ndTrigger) {              // count time  until phototransistor receives light again
33    delay(interval);                       //  Delay for defined time
34    timerCount = timerCount+interval;      // Add time  to counter
35    v1 = volts(A1);                        // check A1 phototransistor
36    waitFor2ndTrigger = (v1 < threshold);  // is "false" when phototransistor  receives light again
37    }
38
39  // end timer count and display results
40  Serial.println("Stopped");             // Display " sec." & newline
41  tone(buzzerPin,  880, 50);              // Sound at finish
42  delay(80);
43  tone(buzzerPin, 880,  80);
44  Serial.print("Final Time = ");          // Display "Final Time = "
45  Serial.print(timerCount/1000);          // Display timerCount in #.### format  instead of milliseconds
46  Serial.println(" seconds");             // Display  " sec." & newline
47  Serial.print("Speed = ");               // Display "Speed  = "
48  Serial.print(72/(timerCount/1000));     // Display speed based on 72 mm  car
49  Serial.println(" mm/sec");              // Display "mm/sec" & newline
50  Serial.println("");                     // print blank line
51  delay(3000);                            // wait 3 seconds and reset
52}
53                                           
54float  volts(int adPin)                       // Measures volts at adPin
55{                                            //  Returns floating point voltage
56 return float(analogRead(adPin)) * 5.0 / 1024.0;
57}    
58

/* PhototransistorVoltage Hot Wheels Timer
 * Power phototransistor  with 5v and GND
 * Connect the phototransistors yellow wire into A1 
 * Optional:  Use a piezo buzzer connected to pin 4 and GND.
 */

const int buzzerPin  = 4;  // other end of buzzer connected to GND
float threshold = 0.25;    // voltage  where phototransistor shows car is in the way
const int interval = 5;  // accuracy  of timer in milliseconds

void setup()                                 //  Built-in initialization block
{
  Serial.begin(9600);                        //  Set data rate to 9600 bps
}

float v1, timerCount;
boolean waitFor2ndTrigger;

void  loop() {
  tone(buzzerPin, 440*6, 50);                   // Sound "ready"
  timerCount = 0;
  waitFor2ndTrigger = true;
  v1 = volts(A1);                                //  measure voltage from phototransister in A1
  tone(buzzerPin, 880, 150);                     //  Sound for start of waiting for trigger
  Serial.println("Waiting for trigger...");      // wait for  phototransistor to be dimmed
  while (v1 > threshold) { 
   delay(interval);                   // otherwise it's too fast to notice button  press ((when one is used)
   v1 = volts(A1);                    // measure voltage  from phototransister in A1
    }
  Serial.print("Started...");                    //  Display "Start"
  
  while (waitFor2ndTrigger) {              // count time  until phototransistor receives light again
    delay(interval);                       //  Delay for defined time
    timerCount = timerCount+interval;      // Add time  to counter
    v1 = volts(A1);                        // check A1 phototransistor
    waitFor2ndTrigger = (v1 < threshold);  // is "false" when phototransistor  receives light again
    }

  // end timer count and display results
  Serial.println("Stopped");             // Display " sec." & newline
  tone(buzzerPin,  880, 50);              // Sound at finish
  delay(80);
  tone(buzzerPin, 880,  80);
  Serial.print("Final Time = ");          // Display "Final Time = "
  Serial.print(timerCount/1000);          // Display timerCount in #.### format  instead of milliseconds
  Serial.println(" seconds");             // Display  " sec." & newline
  Serial.print("Speed = ");               // Display "Speed  = "
  Serial.print(72/(timerCount/1000));     // Display speed based on 72 mm  car
  Serial.println(" mm/sec");              // Display "mm/sec" & newline
  Serial.println("");                     // print blank line
  delay(3000);                            // wait 3 seconds and reset
}
                                           
float  volts(int adPin)                       // Measures volts at adPin
{                                            //  Returns floating point voltage
 return float(analogRead(adPin)) * 5.0 / 1024.0;
}

Dual photogate code

arduino

Using two identical photogates to measure the speed of a Hot Wheels car going either direction. The code allows the photogates to work in either direction.

1/* PhototransistorVoltage Hot Wheels Timer
2 * Power each phototransistor   with 5v and GND
3 * Connect the 2 phototransistors yellow wires 
4 *       into   A1 & A2 to detect start and stop of car.
5 * Use a piezo buzzer connected to pin   4 and GND.
6 */
7
8const int buzzerPin = 4;  // other end of buzzer connected   to GND
9float threshold = 0.25;    // voltage where phototransistor shows car   is in the way
10const int interval = 10;  // accuracy of timer in milliseconds
11
12void   setup()                                 // Built-in initialization block
13{
14   Serial.begin(9600);                        // Set data rate to 9600 bps
15}
16
17float   v1, v2, timerCount;
18boolean v1trigger, waitFor2ndTrigger;
19int count=0;
20
21void   loop() {
22  tone(buzzerPin, 440*6, 50);                   // Sound "ready"
23   timerCount = 0;
24  count = 0;
25  v1 = volts(A1);                      // measure   voltage from phototransister in A1
26  v2 = volts(A2);                      //   measure voltage from phototransister in A2
27  Serial.println("Waiting...");        // wait for either phototransistor to be dimmed
28  while (v1 > threshold   && v2 > threshold) { 
29   delay(interval);                   // otherwise it's   too fast to notice button press
30    v1 = volts(A1);                    // measure   voltage from phototransister in A1
31    v2 = volts(A2);                    //   measure voltage from phototransister in A2
32    }
33  v1trigger = (v1 < threshold);   // find which was triggered 
34  Serial.println("Start");                    //   Display "Start"
35  tone(buzzerPin, 880, 150);                          // Sound   for start of clock
36  v1 = volts(A1);
37  v2 = volts(A2);
38  waitFor2ndTrigger   = true;                // check only A1 phototransistor
39  
40  while (waitFor2ndTrigger)   {              // count time until 2nd probe is triggered
41    delay(interval);                        // Delay for defined time
42    timerCount = timerCount+interval;   
43    v1 = volts(A1);
44    v2 = volts(A2);
45    if (v1trigger) {
46      waitFor2ndTrigger   = (v2 > threshold); // check A2 phototransistor
47    } 
48    else {
49      waitFor2ndTrigger   = (v1 > threshold); // check A1 phototransistor
50    }
51  }
52
53  // end   timer count and display results
54  tone(buzzerPin, 880, 50);                   //   Sound at finish
55  delay(80);
56  tone(buzzerPin, 880, 80);
57  Serial.print("Final   Time = ");       // Display "v  Final Time = "
58  Serial.print(timerCount/1000);        // Display timerCount in #.### format
59  Serial.println(" sec.");             //   Display " sec." & newline
60  Serial.println("");                  // print   blank line
61  delay(3000);                         // wait 3 seconds and reset
62}
63                                            
64float volts(int adPin)                       //   Measures volts at adPin
65{                                            // Returns   floating point voltage
66 return float(analogRead(adPin)) * 5.0 / 1024.0;
67}     
68

/* PhototransistorVoltage Hot Wheels Timer
 * Power each phototransistor   with 5v and GND
 * Connect the 2 phototransistors yellow wires 
 *       into   A1 & A2 to detect start and stop of car.
 * Use a piezo buzzer connected to pin   4 and GND.
 */

const int buzzerPin = 4;  // other end of buzzer connected   to GND
float threshold = 0.25;    // voltage where phototransistor shows car   is in the way
const int interval = 10;  // accuracy of timer in milliseconds

void   setup()                                 // Built-in initialization block
{
   Serial.begin(9600);                        // Set data rate to 9600 bps
}

float   v1, v2, timerCount;
boolean v1trigger, waitFor2ndTrigger;
int count=0;

void   loop() {
  tone(buzzerPin, 440*6, 50);                   // Sound "ready"
   timerCount = 0;
  count = 0;
  v1 = volts(A1);                      // measure   voltage from phototransister in A1
  v2 = volts(A2);                      //   measure voltage from phototransister in A2
  Serial.println("Waiting...");        // wait for either phototransistor to be dimmed
  while (v1 > threshold   && v2 > threshold) { 
   delay(interval);                   // otherwise it's   too fast to notice button press
    v1 = volts(A1);                    // measure   voltage from phototransister in A1
    v2 = volts(A2);                    //   measure voltage from phototransister in A2
    }
  v1trigger = (v1 < threshold);   // find which was triggered 
  Serial.println("Start");                    //   Display "Start"
  tone(buzzerPin, 880, 150);                          // Sound   for start of clock
  v1 = volts(A1);
  v2 = volts(A2);
  waitFor2ndTrigger   = true;                // check only A1 phototransistor
  
  while (waitFor2ndTrigger)   {              // count time until 2nd probe is triggered
    delay(interval);                        // Delay for defined time
    timerCount = timerCount+interval;   
    v1 = volts(A1);
    v2 = volts(A2);
    if (v1trigger) {
      waitFor2ndTrigger   = (v2 > threshold); // check A2 phototransistor
    } 
    else {
      waitFor2ndTrigger   = (v1 > threshold); // check A1 phototransistor
    }
  }

  // end   timer count and display results
  tone(buzzerPin, 880, 50);                   //   Sound at finish
  delay(80);
  tone(buzzerPin, 880, 80);
  Serial.print("Final   Time = ");       // Display "v  Final Time = "
  Serial.print(timerCount/1000);        // Display timerCount in #.### format
  Serial.println(" sec.");             //   Display " sec." & newline
  Serial.println("");                  // print   blank line
  delay(3000);                         // wait 3 seconds and reset
}
                                            
float volts(int adPin)                       //   Measures volts at adPin
{                                            // Returns   floating point voltage
 return float(analogRead(adPin)) * 5.0 / 1024.0;
}

Single LED Photogate

arduino

Single photogate code for measuring of the speed of a single Hot Wheels car. The code allows the photogate to work in either direction.

1/* PhototransistorVoltage Hot Wheels Timer
2 * Power phototransistor
3  with 5v and GND
4 * Connect the phototransistors yellow wire into A1 
5 * Optional:
6  Use a piezo buzzer connected to pin 4 and GND.
7 */
8
9const int buzzerPin
10  = 4;  // other end of buzzer connected to GND
11float threshold = 0.25;    // voltage
12  where phototransistor shows car is in the way
13const int interval = 5;  // accuracy
14  of timer in milliseconds
15
16void setup()                                 //
17  Built-in initialization block
18{
19  Serial.begin(9600);                        //
20  Set data rate to 9600 bps
21}
22
23float v1, timerCount;
24boolean waitFor2ndTrigger;
25
26void
27  loop() {
28  tone(buzzerPin, 440*6, 50);                   // Sound "ready"
29
30  timerCount = 0;
31  waitFor2ndTrigger = true;
32  v1 = volts(A1);                                //
33  measure voltage from phototransister in A1
34  tone(buzzerPin, 880, 150);                     //
35  Sound for start of waiting for trigger
36  Serial.println("Waiting for trigger...");
37      // wait for  phototransistor to be dimmed
38  while (v1 > threshold) { 
39
40   delay(interval);                   // otherwise it's too fast to notice button
41  press ((when one is used)
42   v1 = volts(A1);                    // measure voltage
43  from phototransister in A1
44    }
45  Serial.print("Started...");                    //
46  Display "Start"
47  
48  while (waitFor2ndTrigger) {              // count time
49  until phototransistor receives light again
50    delay(interval);                       //
51  Delay for defined time
52    timerCount = timerCount+interval;      // Add time
53  to counter
54    v1 = volts(A1);                        // check A1 phototransistor
55
56    waitFor2ndTrigger = (v1 < threshold);  // is "false" when phototransistor
57  receives light again
58    }
59
60  // end timer count and display results
61
62  Serial.println("Stopped");             // Display " sec." & newline
63  tone(buzzerPin,
64  880, 50);              // Sound at finish
65  delay(80);
66  tone(buzzerPin, 880,
67  80);
68  Serial.print("Final Time = ");          // Display "Final Time = "
69
70  Serial.print(timerCount/1000);          // Display timerCount in #.### format
71  instead of milliseconds
72  Serial.println(" seconds");             // Display
73  " sec." & newline
74  Serial.print("Speed = ");               // Display "Speed
75  = "
76  Serial.print(72/(timerCount/1000));     // Display speed based on 72 mm
77  car
78  Serial.println(" mm/sec");              // Display "mm/sec" & newline
79
80  Serial.println("");                     // print blank line
81  delay(3000);
82                            // wait 3 seconds and reset
83}
84                                           
85float
86  volts(int adPin)                       // Measures volts at adPin
87{                                            //
88  Returns floating point voltage
89 return float(analogRead(adPin)) * 5.0 / 1024.0;
90}
91    
92

/* PhototransistorVoltage Hot Wheels Timer
 * Power phototransistor
  with 5v and GND
 * Connect the phototransistors yellow wire into A1 
 * Optional:
  Use a piezo buzzer connected to pin 4 and GND.
 */

const int buzzerPin
  = 4;  // other end of buzzer connected to GND
float threshold = 0.25;    // voltage
  where phototransistor shows car is in the way
const int interval = 5;  // accuracy
  of timer in milliseconds

void setup()                                 //
  Built-in initialization block
{
  Serial.begin(9600);                        //
  Set data rate to 9600 bps
}

float v1, timerCount;
boolean waitFor2ndTrigger;

void
  loop() {
  tone(buzzerPin, 440*6, 50);                   // Sound "ready"

  timerCount = 0;
  waitFor2ndTrigger = true;
  v1 = volts(A1);                                //
  measure voltage from phototransister in A1
  tone(buzzerPin, 880, 150);                     //
  Sound for start of waiting for trigger
  Serial.println("Waiting for trigger...");
      // wait for  phototransistor to be dimmed
  while (v1 > threshold) { 

   delay(interval);                   // otherwise it's too fast to notice button
  press ((when one is used)
   v1 = volts(A1);                    // measure voltage
  from phototransister in A1
    }
  Serial.print("Started...");                    //
  Display "Start"
  
  while (waitFor2ndTrigger) {              // count time
  until phototransistor receives light again
    delay(interval);                       //
  Delay for defined time
    timerCount = timerCount+interval;      // Add time
  to counter
    v1 = volts(A1);                        // check A1 phototransistor

    waitFor2ndTrigger = (v1 < threshold);  // is "false" when phototransistor
  receives light again
    }

  // end timer count and display results

  Serial.println("Stopped");             // Display " sec." & newline
  tone(buzzerPin,
  880, 50);              // Sound at finish
  delay(80);
  tone(buzzerPin, 880,
  80);
  Serial.print("Final Time = ");          // Display "Final Time = "

  Serial.print(timerCount/1000);          // Display timerCount in #.### format
  instead of milliseconds
  Serial.println(" seconds");             // Display
  " sec." & newline
  Serial.print("Speed = ");               // Display "Speed
  = "
  Serial.print(72/(timerCount/1000));     // Display speed based on 72 mm
  car
  Serial.println(" mm/sec");              // Display "mm/sec" & newline

  Serial.println("");                     // print blank line
  delay(3000);
                            // wait 3 seconds and reset
}
                                           
float
  volts(int adPin)                       // Measures volts at adPin
{                                            //
  Returns floating point voltage
 return float(analogRead(adPin)) * 5.0 / 1024.0;
}

Dual photogate code

arduino

Using two identical photogates to measure the speed of a Hot Wheels car going either direction. The code allows the photogates to work in either direction.

1/* PhototransistorVoltage Hot Wheels Timer
2 * Power each phototransistor  with 5v and GND
3 * Connect the 2 phototransistors yellow wires 
4 *       into  A1 & A2 to detect start and stop of car.
5 * Use a piezo buzzer connected to pin  4 and GND.
6 */
7
8const int buzzerPin = 4;  // other end of buzzer connected  to GND
9float threshold = 0.25;    // voltage where phototransistor shows car  is in the way
10const int interval = 10;  // accuracy of timer in milliseconds
11
12void  setup()                                 // Built-in initialization block
13{
14  Serial.begin(9600);                        // Set data rate to 9600 bps
15}
16
17float  v1, v2, timerCount;
18boolean v1trigger, waitFor2ndTrigger;
19int count=0;
20
21void  loop() {
22  tone(buzzerPin, 440*6, 50);                   // Sound "ready"
23  timerCount = 0;
24  count = 0;
25  v1 = volts(A1);                      // measure  voltage from phototransister in A1
26  v2 = volts(A2);                      //  measure voltage from phototransister in A2
27  Serial.println("Waiting...");       // wait for either phototransistor to be dimmed
28  while (v1 > threshold  && v2 > threshold) { 
29   delay(interval);                   // otherwise it's  too fast to notice button press
30    v1 = volts(A1);                    // measure  voltage from phototransister in A1
31    v2 = volts(A2);                    //  measure voltage from phototransister in A2
32    }
33  v1trigger = (v1 < threshold);  // find which was triggered 
34  Serial.println("Start");                    //  Display "Start"
35  tone(buzzerPin, 880, 150);                          // Sound  for start of clock
36  v1 = volts(A1);
37  v2 = volts(A2);
38  waitFor2ndTrigger  = true;                // check only A1 phototransistor
39  
40  while (waitFor2ndTrigger)  {              // count time until 2nd probe is triggered
41    delay(interval);                       // Delay for defined time
42    timerCount = timerCount+interval;  
43    v1 = volts(A1);
44    v2 = volts(A2);
45    if (v1trigger) {
46      waitFor2ndTrigger  = (v2 > threshold); // check A2 phototransistor
47    } 
48    else {
49      waitFor2ndTrigger  = (v1 > threshold); // check A1 phototransistor
50    }
51  }
52
53  // end  timer count and display results
54  tone(buzzerPin, 880, 50);                   //  Sound at finish
55  delay(80);
56  tone(buzzerPin, 880, 80);
57  Serial.print("Final  Time = ");       // Display "v  Final Time = "
58  Serial.print(timerCount/1000);       // Display timerCount in #.### format
59  Serial.println(" sec.");             //  Display " sec." & newline
60  Serial.println("");                  // print  blank line
61  delay(3000);                         // wait 3 seconds and reset
62}
63                                           
64float volts(int adPin)                       //  Measures volts at adPin
65{                                            // Returns  floating point voltage
66 return float(analogRead(adPin)) * 5.0 / 1024.0;
67}    
68

/* PhototransistorVoltage Hot Wheels Timer
 * Power each phototransistor  with 5v and GND
 * Connect the 2 phototransistors yellow wires 
 *       into  A1 & A2 to detect start and stop of car.
 * Use a piezo buzzer connected to pin  4 and GND.
 */

const int buzzerPin = 4;  // other end of buzzer connected  to GND
float threshold = 0.25;    // voltage where phototransistor shows car  is in the way
const int interval = 10;  // accuracy of timer in milliseconds

void  setup()                                 // Built-in initialization block
{
  Serial.begin(9600);                        // Set data rate to 9600 bps
}

float  v1, v2, timerCount;
boolean v1trigger, waitFor2ndTrigger;
int count=0;

void  loop() {
  tone(buzzerPin, 440*6, 50);                   // Sound "ready"
  timerCount = 0;
  count = 0;
  v1 = volts(A1);                      // measure  voltage from phototransister in A1
  v2 = volts(A2);                      //  measure voltage from phototransister in A2
  Serial.println("Waiting...");       // wait for either phototransistor to be dimmed
  while (v1 > threshold  && v2 > threshold) { 
   delay(interval);                   // otherwise it's  too fast to notice button press
    v1 = volts(A1);                    // measure  voltage from phototransister in A1
    v2 = volts(A2);                    //  measure voltage from phototransister in A2
    }
  v1trigger = (v1 < threshold);  // find which was triggered 
  Serial.println("Start");                    //  Display "Start"
  tone(buzzerPin, 880, 150);                          // Sound  for start of clock
  v1 = volts(A1);
  v2 = volts(A2);
  waitFor2ndTrigger  = true;                // check only A1 phototransistor
  
  while (waitFor2ndTrigger)  {              // count time until 2nd probe is triggered
    delay(interval);                       // Delay for defined time
    timerCount = timerCount+interval;  
    v1 = volts(A1);
    v2 = volts(A2);
    if (v1trigger) {
      waitFor2ndTrigger  = (v2 > threshold); // check A2 phototransistor
    } 
    else {
      waitFor2ndTrigger  = (v1 > threshold); // check A1 phototransistor
    }
  }

  // end  timer count and display results
  tone(buzzerPin, 880, 50);                   //  Sound at finish
  delay(80);
  tone(buzzerPin, 880, 80);
  Serial.print("Final  Time = ");       // Display "v  Final Time = "
  Serial.print(timerCount/1000);       // Display timerCount in #.### format
  Serial.println(" sec.");             //  Display " sec." & newline
  Serial.println("");                  // print  blank line
  delay(3000);                         // wait 3 seconds and reset
}
                                           
float volts(int adPin)                       //  Measures volts at adPin
{                                            // Returns  floating point voltage
 return float(analogRead(adPin)) * 5.0 / 1024.0;
}

Downloadable files

1 photogate

Single photogate schematic

1 photogate

Single photogate schematic

1 photogate

2 photogates

Two photogates schematic

2 photogates

Two photogates schematic

2 photogates

Documentation

Photogate Holder

Holder for photogate parts that sits under a standard flexible Hot Wheels track.

Photogate Holder

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