Live Audience Response System

[Sean_Fahey]

Hello All,

New member here. I'm looking for some help or suggestions on a project that I was given recently. This project is a system that would take approx. 300 people in a live audience and allow them to make a selection on a multiple choice question on a big screen, using a handheld device. that information would be sent to a computer and totaled to be show on a bar graph (The Who Want's To Be A Millionaire ask the audience deal).

Some things to note:
The data needs to come in live( meaning the bars are rising as the selections are made.
I can have the data in any format and then will convert it to whatever protcall the graphic guys ask for.
It would not be wireless, but have a handheld device that would give them a way to select 1 of the 4 options.

I have thought a few ways to try this, but I'm really better at repair than design. Any ideas or thoughts, suggestions on how to approach this project?

Thank you!
Sean

 

[(*steve*)]

I was just in an audience that had to do this.

The instructions started out with... "Get out your phone and download the app xxxx from your app store. When asked, put in the number yyyyy..."

Worked like a charm. Everyone had their own touch screen device and the organiser didn't have to worry about capital cost, setup, maintenance, etc.

I can't even remember the app we used, but if you google "app to allow audience voting" you'll find there's a stack of them.

 

[Sean_Fahey]

Thanks Steve for the reply. Yes I am aware of these apps. One is Kahoot that uses a smart phone. Unfortunately, when 300 people are all using this type of system at the same time, you will get lag results, and some phones won't even get a choice selection sent by the alloted time period. Also, some audience members will have issues loading the app, and even having to rely on audience member's smart phones working is risky. This will need to be pretty much bullet proof that all 300 people's selection is counted.

Plus, I'm also interested in the thoughts of how it could be done. For example having a handheld unit, with a thumb wheel to select the answer from 1,2,3 or 4, then press a button to send it, which would be binary coded, then somehow serialized onto a RS-232 or 422 or 485 data stream then have a computer Software program pull the data of the com port and do the calculation results. Just thinking off the top of my head, and I'm sure there are other ways to accomplish this. But sometimes I get stuck with how to get the raw binary code onto a stream or something down a wire, so it can be pulled back apart for the data.

Just looking for some help with these thoughts and ideas. Thanks again Steve for the sharing!

Sean

 

[(*steve*)]

In some respects wireless may be easier.

I'd put an ESP8266 module inside a box with a battery and a few buttons. When you press a button it tries to connect to the network. if it fails to connect it backs off for a random time interval before trying again. When it does, it sends its unique ID and your choice then disconnects.

 

[kellys_eye]

Make a chain of 300 resistors with shorting buttons across each of them. Use the chain as one half of a potential divider who's output feeds a simple bar graph generator (LM3914-based?).

The more buttons pressed, the lower the resistance, the higher the 'bar' goes. Rinse and repeat as necessary.

Simple - but the KISS principle always seems to work.

 

[AnalogKid]

I'm leaning that way also. Multiple-choice makes it a bit more messy, but a party-line system is way less complex than 300 individually addressable items to poll continuously.

Cat-5 cable is cheap, relatively reliable, and has 8 wires. That's power, ground, 5 analog outputs, and one reset line.

Each box has 5 buttons. Each button drives a bailing latch, so that whenever a button is pressed it cancels the previous button press. IOW, if you press 2, then change your mind and press 4, the outputs will indicate 2, and then the 2 will go away and 4 will be the output. If you want the box to latch only the first button pressed (a game show circuit), that is a variation of the same circuit. Whatever the logic, the five latch outputs drive five analog switches that feed the output of a single constant current source to one of the five output buses. On each of the 5 output lines, a max of 300 current sources are summed into a terminating impedance. Because the current is coming from a true current source, variations in the analog switch resistances have no effect on the results. The receiving station is basically five load resistors terminating the five analog summing buses, and five opamps to scale the resulting voltage and drive whatever the display system is.

If each current source is 100 uA, then the sum of 300 is 30 mA. Across 100 ohms, that is 3 V, a nice number for modern A/D converters. Depending on how picky you want to be about the resuling voltage, you might not need a calibration adjustment in the current source. A single 12 Vdc source should provide enough headroom for the analog switch resistance, wiring losses, etc.

Sending out a reset pulse clears all latches. As a bonus, you could send an extra-long reset pulse to force all 300 boxes to select button #1, as a way to calibrate the system's peak output voltage.

A voltage source driving a summing resistor will produce a summed voltage that is logarithmic with respect to the number of buttons pressed. A current source will produce a linear result. This approach is how large intercom systems work in production houses and TV studios.

The current source circuit would need 0.1% resistors, but those are cheap these days. The analog buses can be heavily filtered to remove noise pickup without affecting the dynamics of the display.

The wiring path through the audience can be one giant daisy-chain, 300 home runs, or anything in-between. I recommend a ladder pattern because the multiple redundant paths offset minor connector problems.

No microcontrollers, no serial data, no 555's.

ak