Ok, I'm a big boy now but I refuse to grow up! Who's with me on this one?
I've recently found a renewed interest in my old Scalextrics going back to the 60's and 70's and I'm trying to improve the performance of a particular lap counter that I always favoured. It is an electric one where there is a short section of track (about 8 inches length) that is separated from the rest of the circuit and when the car goes over this section the circuit to a solenoid is completed and triggers the lap counter. There are a few problems though in that it relies on good continuity between the pick up braids and track, but this is rarely the case so the result is either multiple triggers as the car goes over the section, or if the car is too quick no trigger at all! Also, as the section is separated from the rest of the track and the motor and solenoid are connected in series as the car geos over, there is little power remaining to drive the car and unless it has some momentum before it gets there it sometimes stops.
I had a bright idea to use that section to trigger a monostable to activate the solenoid, so once triggered it would not re-trigger until the monostable had completed its cycle, by which time the car would be clear of the lap counter section. This would get around the problem of bad contact between braids and track, which it does perfectly.
However, all is not well as it often triggers as the car is driven around the rest of the track, usually on throttle opening, and more so with later more powerful cars.
I've attached my circuit diagram using a 555 timer. As the car goes over the lap counter section power is applied to it via the 8.2Ω resistor, and it is the voltage drop across this resistor that triggers the timer. This way plenty of power is applied to the car over this section. I would have preferred to make it controllable with the throttle but can't think of a way to do it.
However, the main thing I would like to sort out is this false triggering. I have also tried connecting a 100nf cap in series between the BC547 and pin 2 input on the 555 but this has had no effect. The only way I can get around the problem is to connect the lap counters to a separate power supply.
I've recently found a renewed interest in my old Scalextrics going back to the 60's and 70's and I'm trying to improve the performance of a particular lap counter that I always favoured. It is an electric one where there is a short section of track (about 8 inches length) that is separated from the rest of the circuit and when the car goes over this section the circuit to a solenoid is completed and triggers the lap counter. There are a few problems though in that it relies on good continuity between the pick up braids and track, but this is rarely the case so the result is either multiple triggers as the car goes over the section, or if the car is too quick no trigger at all! Also, as the section is separated from the rest of the track and the motor and solenoid are connected in series as the car geos over, there is little power remaining to drive the car and unless it has some momentum before it gets there it sometimes stops.
I had a bright idea to use that section to trigger a monostable to activate the solenoid, so once triggered it would not re-trigger until the monostable had completed its cycle, by which time the car would be clear of the lap counter section. This would get around the problem of bad contact between braids and track, which it does perfectly.
However, all is not well as it often triggers as the car is driven around the rest of the track, usually on throttle opening, and more so with later more powerful cars.
I've attached my circuit diagram using a 555 timer. As the car goes over the lap counter section power is applied to it via the 8.2Ω resistor, and it is the voltage drop across this resistor that triggers the timer. This way plenty of power is applied to the car over this section. I would have preferred to make it controllable with the throttle but can't think of a way to do it.
However, the main thing I would like to sort out is this false triggering. I have also tried connecting a 100nf cap in series between the BC547 and pin 2 input on the 555 but this has had no effect. The only way I can get around the problem is to connect the lap counters to a separate power supply.
