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'Yet another LED project'
1996\11\14@173902 by W. Lee Vick, Jr.

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PIC.gurus,

       I also have a little LED project and was looking for some help with
it. I'd like to build a box which determines the order of finish of a pine
box derby (small wooden cars about 7" by 3" which run down a slotted track)
race. Ideally there will be one micro controlling things, 6 sensors (one for
each lane in the race), and 6 7-segment LED's which will show the position
in which the cars finished, and a button for resetting the system for the
next race. Thanks to info on the 595 I've figured out how to use it for
displaying the race results (or whatever else I want to display). My
questions are about the micro,the sensors, and the LED's:

       1. Can anyone recommend a good IR TX/RX pair which is small, cheap,
and will work over distances of about 3". Also, how do I wire this thing up?
Do I just treat it as a normally open switch?

       2. Any recommendations for 7-segment LED's? Ideally they'd have
current limiting resistors built in (to save wiring - I'm just an engineer
so my wire-wrapping skills are very suspect), be cheap (a recurring theme -
hey, this is for the Cub Scouts and they're not rich), and be as big as
possible (and no, I don't want to pay $5-10US each for 3" high versions).

       3. I figure I need about 14 I/O pins, maybe an INT, and a timer or
two. Which PIC should I use?

       I thank you, and if I can get all this working then the little Cub
Scouts thank you.

                                       Cheers,

                                       Lee.

************************************************************************
* Lee Vick           *   I had a nightmare that I was in an elevator   *
* spam_OUTleevickTakeThisOuTspamti.com     *   with Kenny G and Michael Bolton, a gun, and   *
* +1 713-274-2241    *      just one bullet... So I shot myself.       *
************************************************************************
* Standard disclaimer: TI as an organization is much too smart to      *
*                      to agree with anything I have to say.           *
************************************************************************

1996\11\14@192940 by Steve Hardy

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> From: "W. Lee Vick, Jr." <.....wlvickKILLspamspam@spam@micro.ti.com>
>
> PIC.gurus,
>
>         I also have a little LED project and was looking for some help with
> it. I'd like to build a box which determines the order of finish of a pine
> box derby (small wooden cars about 7" by 3" which run down a slotted track)
> race. Ideally there will be one micro controlling things, 6 sensors (one for
> each lane in the race), and 6 7-segment LED's which will show the position
> in which the cars finished, and a button for resetting the system for the
> next race. Thanks to info on the 595 I've figured out how to use it for
> displaying the race results (or whatever else I want to display). My
> questions are about the micro,the sensors, and the LED's:
>
>         1. Can anyone recommend a good IR TX/RX pair which is small, cheap,
> and will work over distances of about 3". Also, how do I wire this thing up?
> Do I just treat it as a normally open switch?

Since you work for TI (I assume Texas Instruments) they make optoelectronic
devices like this - you should take advantage of your employer's resources.
My employer makes tape drives.  These contain such sensors for determining
whether the tape is loaded.  Unfortunately, I have no idea who actually
makes the sensors.

>
>         2. Any recommendations for 7-segment LED's? Ideally they'd have
> current limiting resistors built in (to save wiring - I'm just an engineer
> so my wire-wrapping skills are very suspect), be cheap (a recurring theme -
> hey, this is for the Cub Scouts and they're not rich), and be as big as
> possible (and no, I don't want to pay $5-10US each for 3" high versions).

A bit optimistic price-wise unless you can find some surplus.  HP make
LED displays.  I got HDSP3400's which are reasonably cheap, a few cm
high and good efficiency.  Current limiting resistors not built-in so
you should use resistor packs if wiring is a problem.

Forget wire wrapping!  Making a PCB is so easy these days.  But first,
prototype the circuit on a breadboard.

>
>         3. I figure I need about 14 I/O pins, maybe an INT, and a timer or
> two. Which PIC should I use?

Well you don't need a timer if you are only interested in the _order_
of events, unless you need an overall timeout in case one of the cars
goes "off the rails".  You don't even need interrupts because the PIC
is fast enough to do everything by polling.  You just set up one humungous
program loop which updates and multiplexes the display, queries the
start button and reads the sensors as appropriate.  The number of I/O
pins is a bit of a killer otherwise you could use an 18-pin device.  You
will have to go for a 28-pinner such as 16C73.

Because of the simple application (not timing or interrupt critical) it
would be easy for you to completely test the software operation using
MPSIM.  This would almost guarantee that you would only have to burn the
EPROM once.

{Quote hidden}

I would have lined them up and plugged both of 'em at once.

Regards,
SJH
Canberra, Australia

1996\11\15@002319 by Tony Matthews

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I would like to suggest omitting the tr/rx modules as they are not
really necessary.A non modulated light source(led..)on one side and a
light detector on the other side (solar cell,photocell,phototransistor)
with a single op_amp 741 a diode two capacitors and two resistors you
get a clean positive or neagative pulse despite varying light conditions
and at very little cost X6 as to where to put the signal learning that
is why I am here.:).Tony M.

W. Lee Vick, Jr. wrote:
{Quote hidden}

1996\11\15@062248 by efoc

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Steve,
       here is my idea... you can use a pic16c84 for this

you will need a BCD to sevensegment decoder driver chip for each 7
segment display a 3 to 8 decoder like the 74138 a binary to decimal
decoder and a few diodes plus the opto switches

now you can set up the optos to conect to the decimal decoder one per
line and also take the output via a diode to the PB0 line take thoutput
from the decimal decoder to the PB1,2,3 lines. now by setting up the pic
so its generates an int when the PB0 line is toggled you can read the
output on the decimal decoder to tell which opto caused it. now for the
output you can connect the input of the bcd to 7 segment driver/decoders
to the PA0,1,2,3 pins and the input of the 3 to 8 decoder to PB4,5,6 the
O/P of the 3 to 8 is used to drive the output enable pins of the bcd to
7 seg decoders. now you can multiplex the outputs with the PB4,5,6 pins
and the number is a binary on the PA0,1,2,3 pins. the software should be
updating the displays in its normal loop from a table updated by the int
loop. finaly a Reset could be achived with the PB7 pin scaned in the
same loop as the multiplexing. There that aint so bad is it. If you need
a hand with the code for the 16C84 give me an Email and i'll try and
help as much as I can.

Cheers Peter.......

--
==================================
= New Ideas come from those who  =
= didn't know it wasn't possible =
==================================

1996\11\15@093622 by W. Lee Vick, Jr.

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Steve,

       A few comments on your comments (for you and others to comment on)...

>>         1. Can anyone recommend a good IR TX/RX pair which is small, cheap,
>> and will work over distances of about 3". Also, how do I wire this thing up?
>> Do I just treat it as a normally open switch?
>
>Since you work for TI (I assume Texas Instruments) they make optoelectronic
>devices like this - you should take advantage of your employer's resources.
>My employer makes tape drives.  These contain such sensors for determining
>whether the tape is loaded.  Unfortunately, I have no idea who actually
>makes the sensors.

       Well, TI is HUGE and I don't work anywhere near anyplace where they
make these sensors. It's not like we have a company store where we can go
and pick up sensors, chips, laptops, or missiles cheap (TI makes all those
things and more). One would hope it would be a little easier to get things
from inside but in companies as big as this that's not always possible.

{Quote hidden}

       OK, what I meant to say was that I can live with 1" high LED's but
if someone happened to know where I could get 2" for the same price, I'd be
happy to hear that. Define reasonably cheap for those HDSP3400's.

{Quote hidden}

       Right, I want the timer so I can set up a loop to shift the current
data I want to display out to the display circuitry and then latch it in -
this loop would be run every half second or so. Start up the system with
dashes displayed where the numbers go, start the timer routine, then all I
have to do is change some RAM locations and the display will take care of
itself. I COULD always do this in the main loop, but I'd rather loop on
polling the lane sensors to keep the resolution small.

>> ************************************************************************
>> * Lee Vick           *   I had a nightmare that I was in an elevator   *
>> * .....leevickKILLspamspam.....ti.com     *   with Kenny G and Michael Bolton, a gun, and   *
>> * +1 713-274-2241    *      just one bullet... So I shot myself.       *
>> ************************************************************************
>
>I would have lined them up and plugged both of 'em at once.

       Thought of that. But there is the possibility the bullet would
deflect and not handle the one in the back. This is one where ya gotta go
with the worst case scenario. ;-)

       Thanks!

                                       Cheers,

                                       Lee.

1996\11\15@113546 by fastfwd

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W. Lee Vick, Jr. <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU> wrote:

> I'd like to build a box which determines the order of finish of
> a pine box derby (small wooden cars about 7" by 3" which run down a
> slotted track) race. Ideally there will be one micro controlling
> things, 6 sensors (one for each lane in the race), and 6 7-segment
> LED's which will show the position in which the cars finished, and a
> button for resetting the system for the next race.

Lee:

It's been done.  If you're only interested in HAVING one of these
things, rather than in BUILDING it, call John Shreffler at New
Directions, Inc.  He sells something called "The Judge"... LCD timer;
2- to 8-lane capability; 1st, 2nd, and 3rd-place indicators, etc.

New Directions can be reached at 703 319 0840.

-Andy

Andrew Warren - fastfwdspamspam_OUTix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1996\11\16@081521 by Matthew Mucker

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At 04:30 PM 11/14/96 -0600, you wrote:
>PIC.gurus,
>

>        2. Any recommendations for 7-segment LED's? Ideally they'd have
>current limiting resistors built in (to save wiring - I'm just an engineer
>so my wire-wrapping skills are very suspect), be cheap (a recurring theme -
>hey, this is for the Cub Scouts and they're not rich), and be as big as
>possible (and no, I don't want to pay $5-10US each for 3" high versions).
>

Lee,

I would again recommend Maxim's 7219 chip.  No current limiting resistors
needed, will drive up to 8 seven segment displays, and only takes three
output pins.  I have code to dirve the 7219 and will share it with any
interested parties.  The datasheet is available online from Maxim.

Digi-Key sells these little puppies, but they're not cheap-- about $8.25
each.  However, for what they do, in my opinion they're worth every cent.
Sure makes designing hardware a whole lot easier, and uses three pins to
drive up to 64 individual LEDs.  And yes, though it's designed to drive
seven segment displays, you can configure the chip (quite easily) to drive
an 8x8 (or smaller) matrix of LEDs.

-Matt

1996\11\19@003448 by Barry Bine

picon face
>        I also have a little LED project and was looking for some help with
>it. I'd like to build a box which determines the order of finish of a pine
>box derby <snip> 6 7-segment LED's which will show the position
>in which the cars finished <snip>

       You can simplify things in one of two ways... dump the 7-seg LED's
and just use 36 discrete LED's as follows (example):

Car # >         1  2  3  4  5  6

Position   1st        X
          2nd  X
          3rd              X
          4th     X
          5th           X
          6th                 X

       Or... interface your PIC's serial port to a PC and use either a dumb
terminal program or some quick and dirty program to display results.  The
only problem with this will be performing RS-232 level conversion.

>        1. Can anyone recommend a good IR TX/RX pair which is small, cheap,
>and will work over distances of about 3". Also, how do I wire this thing up?
>Do I just treat it as a normally open switch?

       I have had good luck with IR pairs from Radio Shack... about $2 or
$3 a pair.  If you use an IR detector you'll have to drive the base of an
NPN switching transistor (15 for $3 at RS) in order to amplify the levels as
follows:

       +5   +5
       |     |
       /     /
       \     \_________ Active low
       /     /          input to PIC
       \   |/
       |___|
       |   |\
    IR V     |
       -     |
       |     |
      ---   ---
       -     -

       Even cheaper and easier is to use CDS photocells from Radio Shack
and just use the AD inputs of a PIC16C74.  Look for a sudden drop in light
levels (increase in voltage):

       +5
       |
       /
       \
       /
       \___________analog input to PIC
       |
       |
  photoresistor
       |
      ---
       -

       Pick your resistors experimentally.  Place the photoresistor so that
the car passes over it.

       Have fun...

                                       - Barry

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