Do you need an overhead projector.

你需要用高射投影仪吗？

A transparency for use with an overhead projector.

使用高射投影仪观看的幻灯片。

Sure. Do you need an overhead projector or anything?

当然。你需要用投影仪吗？

Our teacher sent us to the av room for an overhead projector.

老师派我们到视听教室去取投影仪。

Consider using a flip chart, overhead projector or a blackboard.

可以考虑利用一个活动挂图，投影仪或者一个黑板。