DerbyTimer
Simple derby car timer - for gravity fed races at Henry's his demos. (https://vimeo.com/383797381)
Setup
Install photo diode sensor at finish. Make sure that the LED goes on/off as a car passes. Adjust the variable resistor as needd.
Wire something to the servo motor to hold the car.
Reset the unit after powerup -the servo can make it upset.
Racing
- Place the car
- Display should show waiting.
- Press the red button
- Ready .. set... go
- timer runs
- Passes the photo cell and timer stops.
- Press the red button to reset it for the next race.
Pressing the red button during a race will also reset the timer.
The serial port outputs the same at a baud rate of 115200 baud.
Electronics
Simple photo cell - in reverse bias to an LM386 opmap; one pin to a variable resistor to set the cut-off; the other pin to the diode and a 300k resitor devider. With an transistor to up the opamp output to drive an LED.
Servo is directly controlled with a PWM from the arduino. Unfortunately the 'wrong' ever running type.
Start button is wired between GPIO pin and ground. And needs SW pullup.
Buzzer is a simple transitor on a GPIO.