Nuts & Volts - September 2004

Q&A

www.dicomse.com.ar/

In case you want to do a work-around using present-day MCU/logic chips, here is a pinout of the MM5314N:

http://users.otenet.gr/~ath sam/Data_Base/MM5314N_clock _alarm.htm

(the hex file) from the Nuts & Volts website, my computer can’t open it. Do I need a special program or software to view this file? I sure would like to see the code, as I am interested in building the project.

Brian via Internet

Cassette To PC

Q. I have a collection of vinyl records and cassette tapes that I would like to copy over to my PC. However, my system is an older, bookshelf stereo with no line-in or line-out jacks. It does have a 1/4 inch headphone jack, though, which I plan to use.

If possible, I would like to listen to the music while copying. How much power is needed by the line-in input of the sound card and how much is needed by the headphones? Do I need a circuit to reduce the headphone signal?

Dean Hansen New Lisbon, WI

directly feed the sound card line input as long as you have a compatible patch cable (1/4” to 3. 5 mm stereo, in your case) and adjust the playback system’s volume control to provide a solid signal without distortion. No special electronics are required.

All you have to do is tap into this line for monitoring — but it has to be done without pulling down the line with low impedance earphones. What I suggest is a low power headphone amplifier — like the LM4808 — to isolate the headphones from the sound card. The chip is available from Digi-Key. A typical circuit is shown in Figure 6.

I’ve adjusted the values for 4. 5 volt operation — three AA cell batteries, which you can replace with a 5 volt wall-wart. Also, note that I’m using R1 for the volume control. Adjust it to your needs; the lower the resistance, the louder the sound. Of course, you have to supply all the cable breakouts and end connectors. RadioShack should have what you need.

A. I’ve been monitoring a CD-ROM chat room for a while now and have learned a lot about the transfer of record/tape to a PC’s hard disk. One thing I learned is that you can use the headphone jack to

Project Needs PIC Burner

Q. In the April 2004 issue, there is a project entitled “Hand-held Messenger” that seems very interesting to me. However, when I try to download the file that contains the code for the micro

+ 4.5V

To PC Sound Card

Figure 6

100k

3.9k

2.2uF

3.9k +

100uF +

R1

10

LM4808

Headphones

2.2uF

3.9k +

+

100uF

+

1uF 100k 3.9k

LEFT RIGHT

Audio Line Monitor

From Stereo

A. When programming a micro-controller (or a CPU, for that matter), you first create a source code file. This file contains all the instructions in computer-ese ( probably assembly or Basic) that you can modify — or just read. However, the microcontroller can’t read computer-ese. It has to work with binary numbers.

So, the source code is converted into hex format, which the chip understands. This is done using another program, called an assembler or compiler. Once converted to hex, all you can see (using WordPad) are long ASCII strings of 0 through 9, and A through F. At this point, you can’t change the program without going back to the source code, making the changes, and generating a new hex file. (Don’t write — I know!)

Just having the hex code isn’t enough. To get the hex file into the microcontroller, you need a burner. This is a piece of hardware that the controller chip plugs into and connects to the serial, parallel, or USB port of your computer. When you run the burner software, the hex file is transferred to the microcontroller’s memory. You’re now set. PIC programmers are plentiful and include