Race Track Timer

[adaschau2]

Hey guys,

Me and my Dad are involved with a local Boy Scout troop which is purchasing a new pinewood derby track and we thought it would be nice to devise a "finish line" apparatus to indicate lane placement and finishing time.  Unfortunately, we are both fairly new to electronics and we could use a little help.

Now, the first of my problems is the 7 segment display.  I've programmed a simple micro-controller to handle one before, but it required each segment to be attached to it's own I/O pin on the controller.  Is there a way around this? 

I included a link to an image of an example timer.  The one we are building is only for a two lane track, but it is a good example of what we are shooting for.

http://farm4.static.flickr.com/3367/3641146679_ebd327b3d2.jpg

[Graynomad]

There are no end of 7-seg display driver chips that will do up to 8 digits and only need 2-3 pins because they use SPI or I2C.

Or you can multiplex yourself, in which case you need an octal high-current driving chip of some kind and one uC output per digit, although there are many different ways to do this as well.

I have no idea what a "pinewood derby track" is, how large are the displays you need, That pic just showed small ones.

______
Rob

[knossos]

For those who don't know, the Pinewood Derby is a gravity powered race of home made cars fabricated from small lightweight blocks of wood with plastic wheels.  They run down an inclined track.  Usually a track has four lanes.

Our pinewood derby track has IR sensors at the end of the track and a serial interface that connects with commercial software that will track times, scores, speed to scale in miles per hour, organizes the race order, etc.  Our track is 4 lanes and has 1 large 7 seg. display per lane that shows the finish order.  All the timing, etc is displayed via the software on a laptop thats connected to a projector.

The IR emitter for each lane is placed below the 7 segment displays at the finish line and aims downward to a small drilled hole in the wood that contains a recessed IR detector. 

In addition there is an IR beam across the tracks at the start line that triggers the counter to start.  Hopefully this information helps.  Sorry, but the name of the software escapes me right now.

[adaschau2]

To Graynomad,
Thanks!  That's what I needed to know.  Now I just have a little studying to do...

To Knossos,
Thank you for the advice.  I was actually planning on using IR sensors for the finish line, although I hadn't thought to use it for the starting line too.  I've been thinking that I'll just rig a switch to open with the start gate.  Thanks for the tips!

[knossos]

Personally I'd probably go with the switch attached to the start myself, but I didn't design ours.