Topic 14: Digital Technology
14.1 Analogue and Digital Signals
1. Convert the following numbers into 8-digit binary
(a) 7 (b) 14 (c 16 (d) 67 (e) 125
2. Convert the following 6-bit binary numbers to base 10 numbers
(a) 000111 (b) 100100 (C) 110011 (d) 111111
3. Write the word BAD in ASCII code
4. If you typed the letter A once every second into a notepad document, how long would it take to fill a 200GB hard drive?
5. Figure 11.8 shows a graph of the varying pd from a microphone. Convert this signal to a digital signal by measuring the pd at a sampling rate of 200 Hz. Round off all of the pds to the nearest whole volt. Draw a graph showing the digital signal.
Does this sampling rate give a true representation of the signal?
6. Repeat with a sampling rate of 400 Hz.
7. To measure the variation of a 50Hz AC signal using a digital device, what is the minimum sampling rate you should use?
8. The following string of 1s and 0s is 3-bit binary data sampled at 2Hz. Turn this data into a table giving time and a number representing the pd. Use this data to draw the signal.
011100101100011000
9. The track on a CD is 5km long and is made up of a series of pits and lands that are a minimum of
0.83 pm long.
(a) How many pits are there on the CD track (remember each pit is followed by a land)?
(b) Each short pit has two edges so represents 2 bits of data. How many bits are there on a CD?
(c) How many bytes of data are there on a CD?
10. A CD can store 74 minutes of stereo music.
(a) If 16 bits are recorded at 44 000 samples per second, how many bits are recorded in 74 minutes?
(b) The music is stereo so there are 2 channels. How many bits must the CD contain?
(c) How many bytes is that?
14.2 Data Capture; Digital Imaging using Charge Coupled Devices (CCDs)
11. What will be the potential difference between the plates of a 15 F capacitor if there is a charge
of 5C on the plates?
12. The capacitance of the photodiodes in a typical CCD is about 100 F. What charge will cause a pd of 1V across it?
13. What is the charge of 50 electrons? If there are 50 electrons stored on a 100 nF photodiode what will the pd across it be?
14. What is the height of a 6mm CCD?
If each pixel is a square of 10 microm side, how many pixels will a 6mm CCD have?
15. A picture of a 10 m high tree is to be taken with a camera containing a 6mm CCD. What is the magnification of the camera if the tree just fits on the CCD?
16. (a) If 1010 photons enter the camera and land on the CCD of a 5 megapixel camera, how many photons land on each photodiode?
(b) If the quantum efficiency is 70%, how many electrons are liberated in each photodiode?
17.If the rate of reading each pixel in the serial register is 5MHz, how long will it take to read all the pixels in a 1 megapixel CCD?
18. A video camera takes 30 pictures per second, If rate of reading pixels is 5 MHz, how many pixels can the camera have?