Hi all,

I'm new here and I would first like to thank you all for this great forum.

I'm a model hobbyist (cars, planes, trains, you name it....) and I'm trying to build a race management system for my HO car racetrack.

I surfed the net for quite some time and found many very interesting information.
I now need experts like you guys to check what I found and tell me if I'm on the right track or not.

I have a RMS software running on an old PC under DOS. It traps the events through the printer port (LPT) and different pins for different events (as some of you may already know).

What I would like to do (for a start...) is :

- Lap counting
- Lap Timing
- "Refuelling" procedure

I found this schematic on the net and I think it's exactly what I need to build

A few comments on the diagram:

Let's consider the drawing and assume that S1 and S2 are on the same lane :

- S1 is a N.O REED switch that detects the pit entry event when "refuelling" is required.
- S2 is a N.O "inverter" REED switch that can signal 2 events (from what I was told...): Pit exit (in the refuelling procedure) and lap counting and timing (on every lap).

Now the questions:

- Do you think such a circuit is what I need for my project ?
- If so, are the component values (resistor,...) OK for a computer printer port (I will have resistance values soon as I need to buy some more equipment - mostly resistors - to test my port "trigger point" without blowing it) ?
On the various sites I checked, resistance should be at least 500 to 1K.

- If not, could you point me to another circuit for my project (I'm sure at least one of your circuits apply to my needs ) ?

I hope I haven't forgotten anything...

Thank you all for your time and support.

Regards,

 

Quite personally I'd do it with optics as in IR LEDs and phototransistors with built in IR filters to exclude normal room light. Mechanical switches are just going to get in the way and possibly derail the cars.

"Interfacing to a printer port" is where all these guys with digital experience come in, I'm basically an analog engineer from DC into the low GHz range with some basic logic experience that's limited to discrete logic ICs. Aside from extremely occasional usage of high-level languages (Visual Basic, C etc) I have't done any machine coding since the days of the 6502 and Z-80 processors.

 

Hello Marshallf3,

Thank you for your answer.
Actually, to make it clearer, I've included another schematic of the way the switches are going to be positionned: they can't be in the way since they're hotglued under the track and the motor magnets activate them when the cars go over them. The slot is intact.

As far as coding, I don't need to since the programs are widely available on the net (Dos and Windows programs). And it's a good thing since I haven't been programming either since the chips you're talking about

 

Didn't even think about the motor magnets, of course the motors these days are quite a bit different from all we had when I was much younger, you can build some truly radical cars nowadays.

And if you want to go gas I think I've seen a 0.21 engine that can crank out in excess of 4 HP but at some insanely high RPM.

 

Just as a bit of trivia, the owner of the local slot car track has a slot car that can do a lap of a ≈150' track in 2.4 seconds. The motor is a "brushed" motor (yes brushed not brushless) and does 240,000 RPM. The body of the car is virtaly a sheet of celuloid with vertical side wing that fold down at speed and suck the car onto the track. I could not beleive it when I first saw it or I should say didn't see it, it was a blur.

 

Too tired to do any math, what does that equate to in mph?

 

Faaaaaaaaaaaaaaaassssssssssssssssssstttttttttttttttttttt


Approx 90 seconds per mile

Scale of the car I think was 1/24th

thats 90 seconds for 24 miles = 16 miles a minute

Scaled speed was something like 960 miles per hour

If that is all wrong please forgive me as the beer is working

mmmmmmmm wonder if that constitutes DUI (computer/calculator)

 

Thank you all for your interest in my project (slot cars lie in the "unconscious" of every kid that has had one at one point.... ).

Yeah, those 1/24th cars are flying (I'm using HO scale - 1/64 to 1/72 - as impressive in terms of handling, speed, etc but a lot easier to deal with in an appartment....) and lexan bodies (if that's what it is) really make a difference compared to hard plastic bodies.

Didn't redo the maths but seems in the acceptable range of answers (last time I tried to get a realistic comparison was something like 700 Km/h for an average car...)

And to come back to my questions guys, any advice ?

 

My understanding is that most high performance cars have magnets strategically placed on thier undercarriage to keep them glued to the track. Could be your trigger.

 

My understanding is that most high performance cars have magnets strategically placed on thier undercarriage to keep them glued to the track. Could be your trigger.

I remember when they started that in HO scale and it did help, the magnets were attracted to the power rails.

 

Right,

With average traction magnet cars, you can turn the rail upside down and the car is still glued...
I run these rockets but I also have the old style cars that drift on every corner . A real pleasure too and a completely different driving experience.

@ GetDeviceInfo: it is my trigger (even the motor magnets are strong enough to activate the Reeds.... so I can run any car - magnet or magnetless - on the track).

Well, my thread sure looks like a slot car forum thread more than an electronics forum thread....

Any suggestions to my questions ?

 

Little up for this thread .

Anyone willing to proofread my homework (hope the subject is not in the wrong section....) ?

Thanks in advance.

 

last up for this question....

I'm a little disappointed that no one took the time to answer an apparently simple question for experts....

I'll just stop bothering all of you guys and try to find answers elsewhere

 

Hi,
you will find the specs for a 'standard' printer port in IEEE documentation.
The port will need to be set to extended capabilities EPP or ECP, honestly cant remember which but LTP only has a couple of fixed inputs ... out of paper, busy .. etc.

In ECP you get to read all the IO lines, programmatically, and there are several activeX controls that will do it reliably under windows.

Electronics .... relatively simple:-
'Most' printer ports are equipped with what are called PullUp resistors, assume yours isn’t and add them, you will want a strong pullup anyway.

These connect the 5 volt rail to the individual IO pin (D0 - D7), via the resistor. This holds it, due to its relatively high input impedance at circa 5V.

If pull-ups are too big the voltage will be to low to reliably read a logic 1 (>4.5v)

Too small and you will attempt to draw too much current from the 5V rail when you 'sink', by connecting it to ground, the IO line/s.

Dammage may occur when:-
1. you try to take too much current as above with too small a pullup
2. you exceed to rated IO line voltage by applying some external power

Obviously you can play with this info and possibly look up the chip and configuration used by your specific port but you will find that a 2K2 (2200Ω) PulUp on each IO pin will do what you need.

Your switches (All normally open) go between the IO line and ground so :-
Switch open - pullUp current to IO pin = logic 1 (pin > 4.5V).
Switch closed - pullUp current 'sunk' to ground = logic 0 (pin < 2V).

If you wanted to invert any or all the IO lines use a buffer, ULN2803A for example, a Darlington array.

Each individual ‘inverting buffer’ input has its own pullup while its output connects to the pulled up input of the port.

Although you now have 16 resistors instead of 8 only 8 will be connected to ground at any one time. Each buffer stage will draw a few μA at its input but this minimal extra current can easily be supplied by the ports 5V rail.

Lastly … you will have to de-bounce the switches, you will probably find parallel 0.01uF cap adequate for this application.

(If you google parallel port interface you will find loads of circuits like this)

Hope all this helps … Have fun.

Al

 

I couldn't really think of anything, this is one of those projects the guys with all the simulators and microcontroller development boards should have been able to spit out in a matter of minutes.

Unfortunately I'm rather limited when it comes to anything beyond dedicated logic ICs from the 74xx and 4xxx days. They still work fine for the times I need to incorporate some simple logic systems into my mainly analog projects.

 

@ Dyslexicbloke: Thanks a lot for taking the time to explain all this. I now need to digest it and I will get back to you to let you know.

@ marshallf3: Of course, I am not blaming anyone, and especially not you who took the time to post a few times here. I was just a little surprised that if the questions I ask are not at a PhD level, almost no one takes the time to contribute...

Guess I will just post my new questions in a slot car forum where at least people are maybe more interested in what I'm saying.

Thanks again to both of you.

 

No problem .... I can do you a schematic if you cant find one elsewhere, but as I said there will be loads of them about.

Glad I could help.
Al

 

Hi Al,

Agree with you, there are tons of schematics on the net, my problem is decidind which one is good for my need!!!

I will move forward with my project as I still have a few things to do before really building the circuit.
What I may ask you later is to proofread my homework to make sure I don't do anything silly....

Thanks again.

Bernard

 

Cool ... just email me if I am not on the board for any reason .... we can continue here then.
Al