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'[EE:] Remote Quiz Buzzers'
2003\11\11@093954 by Michael J. Pawlowsky

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On another board I'm on someone asked about building a "quiz buzzer" system that would have about 20 remotes that need to work up to about 100'.
The buzzer system itself would be very easy to do with a PIC. Basically just monitor a bunch of pins and which ever one goes high first display the number of that PIN on a LCD. And then have a reset button to start monitoring again.

So I'm offering some help for that part of the guys project.

However the remote part is a little harder. At least without it costing alot of extra money.

I was thinking there are 2 possibilities. IR or RF. I don't think IR would be that good because of the range and having many emitters  going off all at once etc. However at least the price per unit would be probably alot cheaper then RF.

But let's say we do go RF. I wouldn't want to have more than one receiver. I've seen then 418Mhz TX/RX packages that have 4-5 outputs. Does anyone know of one that might have 20 outputs? If so what happends when several outputs go off at the same time?

Or do you have any other ideas on how to do this?


Regards,
Mike


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2003\11\11@104014 by Keith L. Kovala

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An idea:

Use the address lines of an encoder/decoder pair to determine which buzzer
was pressed.  In RF apps the address lines of the encoder and decoder must
match for a valid transmit (VT).  Each buzzer would have a specific address
on the encoder and use a PIC to change the values of the address lines of
the decoder and constantly check for a VT.  Once the VT is received you can
then determine which buzzer it is.  Then since you haven't used the data
lines at all your buzzer could actually have a "buzz in" button and some
other options.  Like "give it to someone else" forcing someone the person
buzzing in thinks doesn't know the answer to answer.  I'm sure you could
come up with lots of other options for additional data bits if you wanted.
Additionally, using this method the buzzing in action would be providing the
switch to turn the buzzer on (otherwise even when no data was sent there
would be a VT), thereby extending battery life.

Keith L. Kovala
.....klkKILLspamspam@spam@renderedelement.com

> {Original Message removed}

2003\11\11@123154 by M. Adam Davis

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Without dealing with the analog signal that is being received, and doing
some signal processing on it, it's going to be difficult, at best, to
determine which transmitter (regardless of IR or RF) started
transmission first unless they use different frequencies.

The simple method is to use transmitters that each transmit at a
different carrier, such as IR at 10kHz, 15Khz ...110kHz, or RF at
different channels in the 900MHz spectrum.  In this case the difference
between transmitters may be as simple as changing a coil.

Then you'd need 20 different receivers.  In the IR case it could be a
single IR diode or transister with amplifier, and then a bunch of tone
decoders.

A more complex, but deterministically simple method is to have a PIC in
each transmitter.  Each PIC has a crystal for accurate time keeping.  At
the start, all transmitters are given the current time (to the
millisecond, perhaps) and a time slot in which they are able to transmit.

When the button (or any button on the transmitter) is pushed, the time
is recorded, and during the next available time slot the transmitter
transmits the time of the button press.  The receiver board waits for
the first transmission, then waits for 20 time slots to pass, then
compares the times the buttons were pressed (regardless of when the
signal was received) and picks the winner.

This would work well for any number of transmitters, and each
transmitter could be fairly cheap (a PIC, a crystal, a transmitter, a
battery), though not as cheap as a bare radio transmitter.  The only
constraint is that the more transmitters you have, and the slower the
transmission, the longer you have to wait for a result.

If you use a radio capable of 4800kbps, and give each transmitter a 4
byte slot (two for receiver lock up, one address, one data), with 4
bytes of dead space in between, then you can have 60 time slots per
second.  At 20 transmitters, the time between pressing a button, and
waiting for the result would be 1/3 of a second, which is practically
instantaneous.

You could use this with IR, but I'd wager that radio is better, because
you don't have the line of sight issue, and unless you make the
transmitters really well-shaped, you'll find the contenders holding them
in all sorts of positions - some covering IR windows.  Radio will also
work well for voting, if they can kind of hide it from fellow
contestants (poll the audience type of questions).

Downside is that each transmitter has to be synchronized with the master
console every so often - depending on how tightly the time slots are
spaced, and clock error.  Further, a watchdog reset or power issue in a
transmitter would cause it to not be recognized later.  Autosyching
almost requires some form of two-way communication.  Make it robust, and
extremely simple to synch, and put an 'out of synch' light on the
transmitter.  There are other options, but if it's designed well then
it's still worlds better than trying to decipher 20 transmissions on the
same frequency at the same time.

Makes me want to try it out for the Renasys contest...

Hope this helps.

-Adam

Michael J. Pawlowsky wrote:

{Quote hidden}

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2003\11\11@125305 by Denny Esterline

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<snip>
>
> Downside is that each transmitter has to be synchronized with the
master
> console every so often - depending on how tightly the time slots are
> spaced, and clock error.  Further, a watchdog reset or power issue
in a
> transmitter would cause it to not be recognized later.  Autosyching
> almost requires some form of two-way communication.  Make it robust,
and
> extremely simple to synch, and put an 'out of synch' light on the
> transmitter.  There are other options, but if it's designed well
then
> it's still worlds better than trying to decipher 20 transmissions on
the
> same frequency at the same time.
>

I had a similar problem recently with a datalogger
application -keeping the time synched between differrent units. After
doing an imense amount of research on RTCs and other options I came
about a solution so simple it hurt :-)

1:Keep a running counter at the speed that matches your needed time
resolution.
2:When event happens, capture the count.
3:Include the captured count and the current count in the data packet.
4:The reciever knows what time it recieved the packet, and can
calculate the difference in time between the event and transmit.


The overall error of the transmitter clock becomes less relevant
because the  error is non-cumulative.

This may not be a good fit for your application due to the resolution
you need, but mine only needed about 1 minute resolution.

-Denny

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2003\11\11@130345 by Michael J. Pawlowsky

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Well I agree that this is probably the way to go.
I took a look around for TX/RX modules and found a Lynx unit that supports 100 different channels.

http://rocky.digikey.com/WebLib/Linx%20Technologies/Web%20Data/hp3-rx-man.pdf

But a combination TX/RX comes to about 100$.
So for 20 channels we are probably talking 2500-3000$ or so when we add cases, momentary switches, PCBs etc.

Kind of pricy.




>The simple method is to use transmitters that each transmit at a
>different carrier, such as IR at 10kHz, 15Khz ...110kHz, or RF at
>different channels in the 900MHz spectrum.  In this case the difference
>between transmitters may be as simple as changing a coil.
>
>Then you'd need 20 different receivers.  In the IR case it could be a
>single IR diode or transister with amplifier, and then a bunch of tone
>decoders.

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2003\11\11@133144 by Mike Hudson

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A simple solution would be to have each transmitter transmitting CW on a
different frequency (as M. Adam Davis proposed). Someone 'borrowed' the
ARRL handbook from the lab here, so I can't find the exact schematic,
but I believe you could hack together a simple CW transmitter really
cheaply (<$5 CAD) out of discrete componenets. By using a potentiometer
to adjust the frequency, each TX unit could be identical.

On the receiver side of things, I believe you could downconvert the
entire TX spectrum used by the transmitters, digitize it at a
moderately fast rate (~3x to 5x the IF bandwidth), and then FFT the
thing to find out what transmitters are active. This may be more
expensive than a simple radio modem in the master unit, but as you're
producing 20+ TX units per master, $5 transmitters justify spending
$275 on the master.

Now, the above setup would be rather sensitive to interference, but a
judicious selection of transmit frequencies would definitely help. Read
through RSS-210 / FCC part 15 to find out what frequencies you can use.

I think this scheme would be far more elegant than having to sync
intelligent transmitters with the receiving station. It would also
bring the transmitter size and cost down to a very reasonable level,
although you'd need non-trivial signal processing on the receive end of
things.

In the likely case of problematic interference (we _are_ talking on/off
keying here), you could assign linearly independent CDMA-ish
collections of frequencies to each transmitter. This way after taking
the FFT you could look at the active frequencies and deduce which
transmitters were active. This would complicate the transmitter a
little but increase noise immunity proportionally to the number of
channels used. (If the likelyhood of noise on one channel is x, the
chance of having it on two simultaneously is x^2, etc..)

--
Mike Hudson

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2003\11\11@134012 by SavanaPics

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Not sure if it is feasable, but what would the possibility be of using one
transmitter, and twenty different interlocked tone sources. Say you had one
relay and one tone for each staion. When the first is energized, it locks out the
others causing only the winning tone to be sent. The receive end could them
hold the tone decoder that would detect the tone received and decoding it  to
determine which  station send the winning  button that was pushed.

You may also want to consider the  4 x 5 matrix keypad aproach. I believe the
74C922/24 chips may work as well. If I am not mistaken, they only allow one
key at a time to be pressed, therefore locking the others out. Using this uou
would only have to send  the key being pressed and have the receiving end catch
the winning key and display the winner.

I may be able come up with the relay circuit,  The tone encoding and decoding
could be done with inexpensive pic chips and the decoder could be any of the
later units.

Just a thought

Eddie, kc4awz

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2003\11\11@144247 by Marcel van Lieshout

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Perhaps the nRF24-series from Nordic? They even come with embedded micro
(8051).

http://www.nvlsi.no/index.cfm

They also have a reference-design with pcb-antenna.

Marcel

{Original Message removed}

2003\11\11@162617 by Jinx

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The circuits I've seen for quiz buzzers have a common disable
line. If a button is pressed it buzzes/lights and also sets a logic
condition that de-activates other units. Say you had both a Tx
and Rx in each unit, all on the same frequency. As soon as a
button is pressed all the other units pick up that transmission
and shut down. The only active unit then has the airwaves to
itself and can send whatever is needed without interference

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2003\11\11@164244 by Michael J. Pawlowsky

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O.K. but that will even bring up the cost more.
I will go over all these suggestions and see what we can come up with.

Thanks for all the suggestions!
Mike


*********** REPLY SEPARATOR  ***********

On 11/12/2003 at 10:25 AM Jinx wrote:

>The circuits I've seen for quiz buzzers have a common disable
>line. If a button is pressed it buzzes/lights and also sets a logic
>condition that de-activates other units. Say you had both a Tx
>and Rx in each unit, all on the same frequency. As soon as a
>button is pressed all the other units pick up that transmission
>and shut down. The only active unit then has the airwaves to
>itself and can send whatever is needed without interference

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2003\11\11@172442 by Jinx

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> O.K. but that will even bring up the cost more

Unfortunately two key "response time" graphics in both
Digikey's and Link's pdf are unreadable (even after getting
the once-over with a sharpener). It's possibly in the order of
milliseconds, but without reading all the info I can't be sure

An important function of your project is avoiding near-coincident
button presses. If the Linx unit response time is too long then this
makes it unusable. The beauty of a wired or simple RF system is
that it's dumb but has a very fast response time. The Linx-type
units smartness has a speed trade-off, one that doesn't matter
in non-quiz-buzzer applications

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2003\11\11@181742 by Jinx

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You could make your own transmitters fairly simply

http://w1.859.telia.com/~u85920178/

particularly if you chose a single-frequency system. The Linx
units are high-end, high-performance, which you don't really need.
A couple of transistors and 3V will get you 100ft no problem

There are several FM receiver ICs around, Philips and Brooktree
for example, or go AM with a ZN414 type

Around here a pizza franchise is offering a free FM radio with
a $20 pizza order. Imagine if you could get a hold of a couple
dozen of those and cannibalise them (the radios !! - unless you
happen to be a pizza too). I presume the radios have Asian
innards

More than once I've bought a dirt-cheap consumer product off
the shelf just to hack the keyboard, clock, display, whatever. It
can often work out a heck of a lot cheaper than using "proper"
new components

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2003\11\11@204121 by techy fellow

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If you have access to Elektor Jan 2002 issue, there is a full blown project on this one. The project is using PIC 17Cxxx family and support 4 players (ie. 4 transmitters). I recalled the article mentioned if one player presses a button, the circuit will not response to the rest of the buttons.

cheers,
Davis

SavanaPicsEraseMEspam.....AOL.COM wrote:Not sure if it is feasable, but what would the possibility be of using one
transmitter, and twenty different interlocked tone sources. Say you had one
relay and one tone for each staion. When the first is energized, it locks out the
others causing only the winning tone to be sent. The receive end could them
hold the tone decoder that would detect the tone received and decoding it to
determine which station send the winning button that was pushed.

You may also want to consider the 4 x 5 matrix keypad aproach. I believe the
74C922/24 chips may work as well. If I am not mistaken, they only allow one
key at a time to be pressed, therefore locking the others out. Using this uou
would only have to send the key being pressed and have the receiving end catch
the winning key and display the winner.

I may be able come up with the relay circuit, The tone encoding and decoding
could be done with inexpensive pic chips and the decoder could be any of the
later units.

Just a thought

Eddie, kc4awz

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2003\11\11@205157 by Bob Ammerman

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> A more complex, but deterministically simple method is to have a PIC in
> each transmitter.  Each PIC has a crystal for accurate time keeping.  At
> the start, all transmitters are given the current time (to the
> millisecond, perhaps) and a time slot in which they are able to
transmit....

I'm afraid this won't work too well as is. Assuming the time is reset in the
transmitters once an hour, and that the timing is controlled by a standard
30 ppm crystal, then the error after one hour could be as large as:

   3600 seconds * 30ppm = 0.108 seconds

Obviously this is *not* good enough.

Let's see if we can use this trick to move in the right direction however.

I'd look at using a rfPIC12F67x transmitter and rfRXD0x20 receiver in both
the slave and base units.

Now the base unit can regularly send out a poll that informs the
transmitters of the current time.
In response to that poll each transmitter sends a packet in a particular
timeslot. That packet can include the most recent keydown time.

A couple neats tricks here are based on the fact that the polling occurs
continuously. This allows the slaves to keep track of the current time. If a
slave misses  a poll or a few due to noise that is ok. It still transmits in
its standard timeslot. Similarly, the master can run thru several poll
sequences before accepting what looks like the first-down from all the
slaves. This allows for packets missed by the master.

Finally, there is a neat way to set up the Ids in each slave:

In configuration mode, the master repeatedly sends out a special packet
that, if effect, says: "Setting up unit N".

When you press the button on a slave while the master is transmitting that
special packet, the slave then simply stores "N" in its eprom to track its
ID (which determines its timeslot).

Note that everything runs on one frequency.

Bob Ammerman
RAm Systems

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2003\11\11@215256 by SM Ling

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I assume it is for 1 or 2 unit, get the eval kit of Lynx.  This was what I
did, they are quite affordable, about US$150-200.

BTW if you have more time, you might want to hack the wireless mouse for
their RF modules, I got one set for US$15 but was not the frequency I could
use.

Cheers, Ling SM

> Well I agree that this is probably the way to go.
> I took a look around for TX/RX modules and found a Lynx unit that supports
100 different channels.
>
>
http://rocky.digikey.com/WebLib/Linx%20Technologies/Web%20Data/hp3-rx-man.pdf
>
> But a combination TX/RX comes to about 100$.
> So for 20 channels we are probably talking 2500-3000$ or so when we add
cases, momentary switches, PCBs etc.
>
> Kind of pricy.

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2003\11\14@115735 by M. Adam Davis

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Well, the cost of a receiver in each box is about $8, but then you have
to add additional code, etc.

Digikey apparently carries some citizen oscillators, CSX-532T SMT TXCO
which have +/-1.5ppm at 25+/-2C and 2.5ppm over the entire temp range
(-30c to +75C).

2.5ppm means they could be off by +-9mS after one hour.

They cost $9 each, though.

But for small teams (10 on each team) and relatively fast transmitters
with small data packets you could easily get an update from each
transmitter more than once a second.

However, I figure that a two-way system is probably better overall
anyway.  It does make the code a bit harder (synchronizing slaves to the
master is non-trivial - doing so over radio is harder), but the benefits
can outweigh the cost
* Have a light on the player's control telling them who has control.
* No need to hand synchronize them.
* Overcome issues such as spurious reset of the control without
retrieving the box.
* Put flash in them, and remotely update for a new game type
* They can contact each other (interesting uses)
* for simple games, no master needed - one 'slave' can assume
mastership, and the lights can tell who pressed first.
* Add an LCD so players can see 'secret' information

For one off cost would be:
Radio (RX and TX) $10 (cheap laipac modules)
Flash PIC, crystal, LED, PCB $10
Project box with membrane keypad $8

So for under $30 per box you can build a full system with all the
flexibility one could want.  Add some simple encryption routines so it's
not trivial to fake a fastest press...

If I only had the time.  Wired quiz show boxes are sold for over $300
for 8 players in two teams.  Just have to make them really durable...

-Adam

Bob Ammerman wrote:

{Quote hidden}

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2003\11\14@180729 by Charles Craft

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If you believe the hype (and after my wife explained that I was going to be the Easter bunny and
Santa soon what else have I got to believe in) then this would be a good application for Zigbee.

Looks like Chipcon has the physical level covered now:
http://www.chipcon.com/index.cfm?kat_id=6&dok_id=104


{Original Message removed}

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