Using garage door remotes as a voting system?

[Steve]

I'm putting together a talent show and want to have the audience vote
for the contestants (on a scale of 1 to 4 would be fine) using wireless
remotes (maybe even garage door openers?) The results would be
received through a computer system and then projected on a screen.
Does anyone have any suggestions as to how such a system might be put
together? Someone told me I should use a heterodyning receiver. I
found a site that seems to have some of the elements:
http://www.automicro.com.tw/ Any ideas as to which samples I should
buy? Thanks for any info or suggestions!

 

[Rich Webb]

I'm putting together a talent show and want to have the audience vote
for the contestants (on a scale of 1 to 4 would be fine) using wireless
remotes (maybe even garage door openers?) The results would be
received through a computer system and then projected on a screen.
Does anyone have any suggestions as to how such a system might be put
together? Someone told me I should use a heterodyning receiver. I
found a site that seems to have some of the elements:
http://www.automicro.com.tw/ Any ideas as to which samples I should
buy? Thanks for any info or suggestions!

150,000 people in a major league stadium or 15 people in the back yard?

A one-time event or expected to be used regularly for some time to come?

A $100 budget or a $100,000 budget?

Cooperating audience members ("Please vote only once") or robust enough
to counter intentional ballot stuffing, fraud, or interference?

Is it bad if some of the voting equipment "walks away"? If it walks
away, is it possible to use it at a later event to vote twice?

 

[John Fields]

I'm putting together a talent show and want to have the audience vote
for the contestants (on a scale of 1 to 4 would be fine) using wireless
remotes (maybe even garage door openers?) The results would be
received through a computer system and then projected on a screen.
Does anyone have any suggestions as to how such a system might be put
together? Someone told me I should use a heterodyning receiver. I
found a site that seems to have some of the elements:
http://www.automicro.com.tw/ Any ideas as to which samples I should
buy? Thanks for any info or suggestions!

---
Have you thought about what will happen if all the voting units
(remotes) are on the same frequency and a couple (or a few, or a lot)
of the audience members transmit their votes at the same time?

The way I'd do it would be to have the remotes be transponders which
are polled by the master. Assign an address to each remote and then
have it send its data when the master sends that address. After the
master receives the data it sends that address again, followed by a
signal which resets the remote so that the data stored in the remote
will be erased and not sent out erroneously during the next round of
voting but before that audience member votes again. Once cleared, the
remote sends the "cleared" signal, letting the master know that it's
ready for next time. The master then goes to the next address and
goes through the same drill, and when it's done there goes through the
rest of the remotes until all the votes are counted and all the
remotes cleared. Another nice thing to do would be to have the master
send out a "time to vote" signal to all of the remotes which would
light an LED on the remote when it was time to vote.

Email me if you'd like me to de$ign up a system for you.

 

[Steve]

Thanks for the replies. I'd like to do this on as low a budget as
possible (under $1000?, under $500? ), and set it up for around 20
people to begin, with the option to expand. Audience members should be
able to vote at the same time and shouldn't be counted twice if they
press the button twice.

There's a keychain transmitter at http://www.automicro.com.tw/ that is
"rolling code" which I understand means that it creates a unique code
every time it's pressed. There's also a shareware program called
"girder" that I think I could use.

John, what are your rates like? Can I save some money by buying stuff
from http://www.automicro.com.tw ?

Agains thanks for any info or suggestions as to how to what I need to
buy to put this together.

 

[John Woodgate]

I'm putting together a talent show and want to have the audience vote
for the contestants (on a scale of 1 to 4 would be fine)

Expect a lot of ties and 'play-offs' if you have such a restricted
scale. 1 to 10 is better, but you really need to process the raw data
into a power series to avoid ties altogether.

With regard to your actual question, if you are starting from learning
about 'heterodyne receivers', think of another solution. You won't have
the radio thing working before Christmas.

 

[[email protected]]

Thanks for the replies. I'd like to do this on as low a budget as
possible (under $1000?, under $500? ), and set it up for around 20
people to begin, with the option to expand.

1000/20 = 50. And thats not leaving any for the master equipment. And
that covers design, parts and assembly.

I'd make a real simple suggestion: a remote with 4 leds on of differing
colors, a snapshot computer cam, and a manual count. You just dont have
budget for something fancy, especially if you cant build much yourself.


That would at least look ok with the right camera angle. In fact, if
its for film use, theres no need for the remotes to work at all, if
your audience cooperates with a bit of colored paper on their lap.


NT

 

[Mike Harrison]

Thanks for the replies. I'd like to do this on as low a budget as
possible (under $1000?, under $500? ), and set it up for around 20
people to begin, with the option to expand. Audience members should be
able to vote at the same time and shouldn't be counted twice if they
press the button twice.

There's a keychain transmitter at http://www.automicro.com.tw/ that is
"rolling code" which I understand means that it creates a unique code
every time it's pressed. There's also a shareware program called
"girder" that I think I could use.

Using keyfob type remotes as-is is not going to work reliably as there will be collisions due to
simulataneous transmissions. Although keyfobs usually send repeated codes, the intervals are likely
to be the same so it would not help the collision problem.

What you need is for each transmitter to send the data several times at random intervals, over a
period of a few seconds.
You need to do some statistics to work out the optimum timings based on packet length, receiver
timing requirements and number of users. Each transmitter would have a unique address so the
receiver could distinguish each user and ignore the repeats.

I would suggest you look for a keyfob that uses the Microchip RFPic 12F parts, as you could change
the firmware to do this, while still having a ready-made RF stage and casing etc.

You would need to write some code at the receiver end, but it would not be especially complicated -
it would just log each address received and the data for that address.

Typical data rates for a cheap hardware keyfob would be 1200 baud. You need to send, say, 2 bytes of
data (12 bits address, 4 bits vote, 1 byte for error checking, and a few bytes of preamble to let
the receiver settle down, so probably about 6-8 bytes total.
This gives a packet length of about 65mS. Even for 20 users, this means that if all timings were
optimum it would take 1.3 seconds for all packets to get through. By the time you have enough
repeats to get good probability of receiving all of them I would think you are well into tens of
seconds if not minutes. This time would also scale nonlinearly with more users.
So you probably want higher performance RF stuff capable of significantly higher baudrates - this is
do-able but may need more expensive hardware - 100Kbit RF modules are available, and the extra cost
is mostly at the receiver so it may be feasible.
I would say you probably want to be using FM, not AM for better data integrity

An alternative would be to have the fobs synchronise into defined timeslots from an external master
controller, however this adds the cost of receive hardware to each keyfob.

 

[[email protected]]

Using keyfob type remotes as-is is not going to work reliably as

there will be collisions due to

simulataneous transmissions. Although keyfobs usually send repeated

codes, the intervals are likely

to be the same so it would not help the collision problem.

What you need is for each transmitter to send the data several times at random intervals, over a
period of a few seconds.
You need to do some statistics to work out the optimum timings based on packet length, receiver
timing requirements and number of users. Each transmitter would have a unique address so the
receiver could distinguish each user and ignore the repeats.

I would suggest you look for a keyfob that uses the Microchip RFPic 12F parts, as you could change
the firmware to do this, while still having a ready-made RF stage and casing etc.

You would need to write some code at the receiver end, but it would

not be especially complicated -

it would just log each address received and the data for that address.

Typical data rates for a cheap hardware keyfob would be 1200 baud.

You need to send, say, 2 bytes of

data (12 bits address, 4 bits vote, 1 byte for error checking, and a few bytes of preamble to let
the receiver settle down, so probably about 6-8 bytes total.
This gives a packet length of about 65mS. Even for 20 users, this means that if all timings were
optimum it would take 1.3 seconds for all packets to get through. By the time you have enough
repeats to get good probability of receiving all of them I would

think you are well into tens of

seconds if not minutes. This time would also scale nonlinearly with more users.
So you probably want higher performance RF stuff capable of

significantly higher baudrates - this is

do-able but may need more expensive hardware - 100Kbit RF modules are available, and the extra cost
is mostly at the receiver so it may be feasible.
I would say you probably want to be using FM, not AM for better data integrity

An alternative would be to have the fobs synchronise into defined

timeslots from an external master

controller, however this adds the cost of receive hardware to each

keyfob.

On $500 the lot, by someone without the skills to do it?


NT

 

[Bob Smith]

I'm putting together a talent show and want to have the audience vote
I don't have an answer but I wonder if there is
a way to build an rf oscillator with four
transmitter frequencies. The tranmit frequency
is the vote for that remote. Would taking the
relative signal strenght of the four frequencies
give you the relative vote count? Can you sum
the votes by summing the RF power? I suppose
you'd want more than one receive antenna and
that you'd want the antennas some distance from
the audience to mitigate the effects of closer
transmitters overwhelming farther transmitters.