WEBVTT - How does a dollar bill changer work?

0:00:00.640 --> 0:00:03.960
<v Speaker 1>Welcome to Brainstuff from house stuff works dot com where

0:00:03.960 --> 0:00:15.000
<v Speaker 1>smart happens. Hi, I'm Marshall Brain with today's question, how

0:00:15.040 --> 0:00:18.759
<v Speaker 1>does a dollar bill changer work? Creating a good bill

0:00:18.880 --> 0:00:21.880
<v Speaker 1>changer is a tough problem. The device has to work

0:00:21.920 --> 0:00:24.800
<v Speaker 1>with all sorts of bills, from crisp new ones to

0:00:25.000 --> 0:00:27.840
<v Speaker 1>ragged old ones, and it has to be reasonably good

0:00:27.840 --> 0:00:31.600
<v Speaker 1>at telling real bills from fakes. The changer also has

0:00:31.640 --> 0:00:33.920
<v Speaker 1>to be able to sense the denomination of the bill.

0:00:34.320 --> 0:00:37.479
<v Speaker 1>In order to accomplish all this, dollar bill changers use

0:00:37.520 --> 0:00:40.960
<v Speaker 1>a variety of technologies. Here are several of the techniques

0:00:41.000 --> 0:00:44.599
<v Speaker 1>that have been tried. Many of the early bill changers

0:00:44.640 --> 0:00:47.400
<v Speaker 1>took advantage of the fact that US bills are printed

0:00:47.440 --> 0:00:51.680
<v Speaker 1>with magnetic inc They could therefore use magnetic heads like

0:00:51.760 --> 0:00:54.560
<v Speaker 1>the ones you'd find at a cassette tape recorder to

0:00:54.680 --> 0:00:57.960
<v Speaker 1>pick up signals from the bills. Areas of the bill,

0:00:58.080 --> 0:01:01.680
<v Speaker 1>like the background behind the President's base, would generate signals

0:01:01.680 --> 0:01:05.360
<v Speaker 1>at a specific frequency, and the detection of this frequency

0:01:05.400 --> 0:01:09.679
<v Speaker 1>would validate the bill. Different bills generate different frequencies, so

0:01:09.720 --> 0:01:13.240
<v Speaker 1>the frequency can also help to determine what the denomination is.

0:01:13.959 --> 0:01:18.200
<v Speaker 1>Genuine dollar bills have a certain conductivity, and checking for

0:01:18.240 --> 0:01:21.560
<v Speaker 1>the resistance of the bill can authenticate it. Inks and

0:01:21.680 --> 0:01:25.480
<v Speaker 1>papers have different fluorescent properties, and these properties can help

0:01:25.560 --> 0:01:29.520
<v Speaker 1>tell real from counterfeit bills. The optical properties of a

0:01:29.560 --> 0:01:33.200
<v Speaker 1>bill or a strip of a bill can be sensed

0:01:33.240 --> 0:01:35.679
<v Speaker 1>with a photo cell or a camera and compared to

0:01:35.760 --> 0:01:40.120
<v Speaker 1>valid patterns stored in memory. Different patterns from different bills

0:01:40.200 --> 0:01:44.399
<v Speaker 1>can determine the domination. A good bill changer will use

0:01:44.480 --> 0:01:47.200
<v Speaker 1>several of these techniques. Because people seem to have a

0:01:47.319 --> 0:01:51.640
<v Speaker 1>very strong desire to outwit bill changers. Bill changers have

0:01:51.760 --> 0:01:54.680
<v Speaker 1>to handle such things as people inserting just half of

0:01:54.720 --> 0:01:58.480
<v Speaker 1>a bill, people inserting bills with strings attached so they

0:01:58.480 --> 0:02:01.640
<v Speaker 1>can jerk them back out, people who try unplugging the

0:02:01.720 --> 0:02:06.160
<v Speaker 1>machine with the bill half inserted, and so on. For

0:02:06.280 --> 0:02:08.600
<v Speaker 1>more on this and thousands of other topics, is it

0:02:08.680 --> 0:02:13.880
<v Speaker 1>How Stuff Works dot com