View Full Version : Gameshow-style wireless (IR) quiz machine...

05-30-2005, 10:14 PM
Hi all,
I am trying to build a gameshow-type quiz machine (I know, not a novel idea, but please read on...). It·will·display·and manage the scores for 4 players on large led displays, and will check which player first pushes his button to answer.·It will also light up flashing light arrays and·play·sounds to cheer the crowd.·The· central console will include·a 2-line LCD display and control buttons·for the gameshow host·to set the scores and reset·the lights. Finally, each player will have a wireless answering button in his hand, since I didn't want to have wires dangling all over the table. This last feature -wireless input- is where I need help.

So, my question is: what is·the best way to transmit·the players' answering signal to the console? Each answering button should consist of the simplest circuitry possible:·button, battery, IR LED, and something that puts information in the signal·(I have to build 4 of those!). I thought of an IR LED that would transmit a short burst·at a specific frequency to identify each player. Is that the best way? If so,·can I pull it off with Resistor-Capacitor circuits·discharging at various rates, or should I use 555 timers? Or something completely different?·

Thanks all,


06-01-2005, 08:08 AM
Most IR remotes transmit a bit stream on a 38khz modulated IR light.
Maybe you could get some cheapie universal remotes and replace all of the buttons with one big button. Make a new box for the remote and have each player close a switch on one of the buttons (player 1 is keypad1, player 2, keypad2, etc).

IIRC, the BOE bots have some example circuits and programs in the documentation on how to control the robots using an IR remote.

Will each contestant have a IR receiver in their podium/table or will there be one receiver next to the host and four transmitters shooting 150' across the stage to the receiver? Personally, I would stick with a wired solution-no need to worry about dead batteries, IR line of sight problems and contestants not pointing the remotes at the receiver.

Post Edited (menehune1) : 6/1/2005 1:13:16 AM GMT

06-01-2005, 08:43 PM
Thanks for the reply.

And you're right about the battery issue. I had decided to go with 555s, but they need to be powered with 4,5V minimum all the time. I don't want to put voltage regulators in each buzzer, so I would need to put 6 or 9v battery packs in each one, plus have some circuit check if batteries are low, plus provide battery charging connectors or easy access to replace batteries... waaaay too much trouble for·push-button buzzers! Getting off the shelv remotes sounds easy and cheap, but not so fun to make.

Therefore, wires are not so bad.·But instead of having a cable going from each buzzer to the console, I would try linking them in a daisy-chain, having only the last one plugged in the console.·I coud create a 2-bit serial protocol (00=player 1, 01=player 2, 10=player 3, 11=player 4) through a 3-conductor wire: Data, Vcc, Gnd. Hey, did I say I was a Newbee???..

I will show off the result in the Project forum when it's done.



Paul Baker
06-01-2005, 09:21 PM
I thought I posted earlier, but I probably forgot to hit submit then closed the window. I see a potential problem with your setup. Even though you intend on using multiple frequencies to pulse the IR for each player, you will experience interference between players. This is because the carrier frequency (the wavelength of the IR LED) will be the same, this means the receiver will see the aggregate of all the signals. To illustrate my point here is a diagram:

__ __ __ __Player 1 _| |__| |__| |__| |__

_____ _____
Player 2 _| |_____| |_____

__ __
| |_____ | |_____
Receiver _| |__| |__

As you can see seperating the two signals would require processing the detector's voltage in the analog domain so you can detect the 4 different states 4 player's IR LEDs can combine (all combinations of 1 player, 2 player, 3 player and 4 players IR LEDs being on simultaneously). Additionally you would have to decompose the signal to extract who is pressing thier button. Since you do not know the phase of each signal, and you cannot assume that each player is pointing thier IR LED at the reciever so that the amplitude of each is the same (someone could be pointing thiers directly at the receiver while someone else isn't), you talking about a system with at least 8 unknown variables. If a solution can be derived it will not be simple or fast. The system may be reducible to fewer unknowns, but I wouldn't want to derive it.

The upshot? you could get seperate IR receivers for each player so that only thier remote is seen by thier detector.

06-01-2005, 10:11 PM
Thanks Paul. Interference between signals could indeed be a problem with this IR setup. Fortunately, the trick here is that when the first player pushes his button, the signal is read in a matter of a couple milliseconds, and the other players' buzzers are disabled. I figured the small delay needed to decode the signal would still be short enough to prevent a second player pushing his button. In the worst and improbable event that 2 or more players would push their button within approximately 0.002 seconds, I could deal with the interference readout simply by having the console calling a "tie", or some special event in the game...

Now that I'm going with a serial wire communication, the same principle will apply: the first response cancels all subsequent ones.

I am even wondering if, instead of using a 2-bit protocol to differentiate the 4 players, I could simply use an analog signal. Depending on a variable resistor in each buzzer, the output voltage would be different for each player. I even am wondering if the players' output could be added and allow the console to see the different combinations·. Using these voltages :·player1=·1v, player2=2v, player3=4v, player4 =8v, unless I am mistaken, any combination of signal would give a different total :

p1 only: 1v···· p2 only: 2v···· p3 only:4v···· p4 only:8v

p1+p2:·· 3v····· p1+p3: 5v···· p1+p4: 9v··· p2+p3: 6v····· p2+p4: 10v····p3+p4: 12v

p1+p2+p3: 7v···· p1+p3+p4:13v···· p1+p2+p4: 11v···· p2+p3+p4: 14v····

p1+p2+p3+p4: 15v

It works!! well, in theory. 15 possible combinations, and 15 different voltage outputs. Those variable resistors will have to be pretty well adjusted...


06-01-2005, 10:15 PM
That will work too, but I would cut the voltages to 1/3. So the max voltage is 5Volts instead of 15V.

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06-02-2005, 12:01 AM
A couple years ago, I bought a game called "Remote Possibilities".· It came with six remote transmitters (each a different color for identification) and a center console which posed questions and kept score for each color.· The center console had an LCD and a voice chip inside.

We had a lot of fun with it.

It might be something you could hack as a starting point.

BTW If I were hard pressed to play this game today I could probably only find two of the remotes.··Occasionally one turns up under the couch.· I have four kids.

Chris I.

06-02-2005, 01:18 AM
Gamgeee said...
Therefore, wires are not so bad. But instead of having a cable going from each buzzer to the console, I would try linking them in a daisy-chain, having only the last one plugged in the console. I coud create a 2-bit serial protocol (00=player 1, 01=player 2, 10=player 3, 11=player 4) through a 3-conductor wire: Data, Vcc, Gnd.

How about using one multiple pair cable like a cat5 cable? Wire two RJ45 sockets into each station which taps one of the four pairs.

controller-->Station 1 in-+-st1 out->St2 in -+- st2 out-->st3in -+- st3out-->st4in -+- st4 out (no cable)
| | | |
Button1 (pair 1) Button 2 (pair 2) Button 3 (pair 3) Button 4 (pair 4)

If you wire the jacks according to the ethernet specs, you may even be able to use standard patch cables to interconnect the units.

Post Edited (menehune1) : 6/1/2005 6:21:57 PM GMT

Paul Baker
06-02-2005, 02:03 AM
You should take a look at this (http://a330.g.akamai.net/7/330/2540/20050325163550/www.edn.com/contents/images/33105di.pdf) reference, it details how to construct a one wire keypad interface. This could be easily modified to your four buttons by eliminating all keypad connections except 1,4,7 and *.