Organising a temporary drive-in movie theatre for 200 year 12 students is a big undertaking, but I can very happily say that last night it went off spectacularly.

Some friends approached me about this project months ago, and, having never been to a drive-in theatre myself, I spent some time researching what it was all about. Here are the main point I found and what we did about them.

Video

The hardest thing about this project was setting up a screen to project onto. On of the school car parks backed onto tennis courts, and we decided to use the court fencing to mount the screen. But we calculated that the screen needed to be three quarters above the court fence, which would require some serious structural planning. Big screens like this are like sails, and the smallest gust of wind produces enormous amounts of force. The screen itself was made up of old canvasses that were spare from the school art department, and came out to about 8 by 4m (the cinescope ratio was chosen because of the content being displayed). In the end the extra height was supported by a tall piece of scaffolding and wooden support beams attached the the sides of the fence.

It turned out to be a very windy day, and we added extra bracing just to be safe. The night was completely still and the screen held up admirably.

The school already had an Optoma EH7700 projector for the indoor theatre, so we were lucky in that regard. Renting the kind of projector needed for throwing such a large image would have been hundreds of dollars which would seriously have eaten into the profits of the event (I’m no expert, but I’d say the EH7700 costs around $20k). We set it up 14m away from the screen and it produced a bright, clear image. Would definitely recommend this projector. We set it up under a tent just in case it rained, but we got lucky and it was a clear night.

Audio

This topic created a bit of a divide between the team. I wanted to transmit the audio over FM radio, while others thought that a few speakers placed around the car park would be enough. In the end we compromised and decided on an FM transmitter with a few speakers at the front as backup.

Buying a capable FM transmitter on a budget turned out to be difficult. There were cheap transmitters, but none of them had the distance or flexibility we needed. Jaycar had a kit which advertised a large range for only $20, but you had solder it yourself, and the only input was a small microphone. So, being the hackers we are we decided to buy the kit and modify it to suit our needs. We assembled it as per the instructions except for the microphone, which we replaced with a 3.5mm audio jack, the power source, which we attached to an XT60 connector to connect our Li-Po batteries, and the antenna, where we attached a much longer one.

Tuning the transmitter was achieved by turning a small screw. The only problem was that when you had the screwdriver touching the screw, the frequency completely changed, so tuning was a slow and painful process. Also, rotating the transmitter or touching the antenna completely changed the tuning. The range, however, was brilliant. FM radio umbrellas out underneath the antenna so we put the transmitter as high on the tent as we could, and we tested a usable range of about 100m radius. When the transmitter was placed on the fourth floor of a building we found ranges of over 500m radius. This thing is a pain to use, but certainly doesn’t lack power. In the end the top of the tent was the simplest option as it covered the car park and was easy to monitor.

On the night we turned the speakers on as some students got our of their cars and socialised up the front, but nonetheless the transmitter worked flawlessly. We did have it completely taped down so that nobody could accidental bump it.

Outcome

I didn’t personally handle the marketing or the budget for the event but in the end there were over 100 students present and the event made more than $500 which will be donated to charity. Although it’s probably not something I’ll get to do again it was a really enjoyable night for all involved and I think it’s really quite a fun event to have from time to time.