>>>READER-TO-READER QUESTIONS AND ANSWERS
when Toshiba abandoned the competing DVD HD format is February 2008.
Peter Stonard
Campbell, CA
[#6083 - May 2008]
How can I configure a small
LCD display as a voltmeter and/or amp
meter?
#1 The raw LCD component is a
glass screen with the LCD liquid
sandwiched inside and transparent
terminals that usually connect to a
socket, ribbon cable, or other PCB-friendly contacts, such as this one
http://tinyurl.com/4hxuv6 An LCD
module is similar but has the driver
electronics embedded on the glass.
The raw display needs the electronics
to be added, and both voltage levels
and timing are critical to operate
the LCD — so an LCD module with
interface electronics is preferred.
Starting with an LCD module,
such as http://tinyurl.com/4enbco
would still require additional circuits to
scale the analog input voltage, rectify
it for AC ranges, and convert it to a
digital data stream that is decoded to
drive the LCD display. There are
custom and Application Specific
Integrated Circuits (ASIC) to do this,
and these are built into commercial
LCD voltmeter modules — which
can be had for little money on
auction sites.
To build an LCD voltmeter from
scratch would be uneconomical but
fun for a hobbyist. A good place to
start is with an Application Specific
96
August 2008
Standard Product (ASSP) like http://
tinyurl.com/4rbvjs. Another approach
would involve a uC (microcontroller)
— many of which have ADC
converters and I/O for driving an LCD
module on a single chip.
Peter Stonard
Campbell, CA
#2 There are basically two ways this
can be done, depending upon the
type of LCD display you want to use.
The easiest way is to use a digital
panel meter (available from quite a
few N&V advertisers), LCD, or LED,
with a voltage divider for the voltmeter application or a shunt for the
ammeter. (Figure 2) The other way is
to use a microcontroller with an A/D
converter driving a HD44780-based
LCD panel. There are several books
which cover this subject quite well:
Programming the PIC Microcontroller
with MBasic by Jack Smith is an excellent starting point using Basic as the
programming language and Advanced
PIC Microcontroller Projects in C by
Dogan Ibrahim if you want to use C.
PIC in Practice by D.W. Smith covers
this subject in assembler. Keep in
mind that the A/D converter will give
you a 10-bit word for most PIC
microcontrollers and needs to be
converted, which is tedious to write in
assembler, but is the fastest alternative.
There are other ways, such as using I2C
or SPI A/D converters (Microchip
Technology's MCP3421 18-bit I2C A/D
or their 22-bit converter).
Walter Heissenberger
Hancock, NH
Figure 2
[#7083 - July 2008]
How can I interface data
collecting hardware (data loggers and
real-time hardware) with Microsoft
Excel through serial or USB ports?
#1 There are two parts to solving
this job. Communication between
the PC and data loggers, and
converting the data to a format that
MS Excel understands. If the data
loggers/real time hardware store the
data, then send it on command; a
serial terminal program (like
Hyperterminal) with "capture to file"
turned on may be used to collect the
data. On the other hand, if the data
loggers send the data as it happens,
then a specialized communication
program is needed. This is because
Hyperterminal isn't designed to have
capture to file left on for long
periods. For a format that MS Excel
understands, I suggest CSV (Comma
Separated Values) files. This would be
done with a program or script that
parses the raw data and creates the
CSV file. A USB-to-serial converter
looks like a serial port, allowing
terminal programs to work over USB
connections. A data logger that has a
USB port — instead of a serial port —
should come with an interface
program for the PC.
Dale Yarker
via email
#2 There are several low cost
Shareware utilities that can read data
from your COM port and populate a
MS Excel spreadsheet, for example:
COMxL RS232C from Lye-tech,
http://tinyurl.com/4ac7xr
Peter Stonard
Campbell, CA
#3 I am assuming that you already
have the serial signal, therefore you
need a software fix. Windmill
Software Ltd. has a free RS-232
instrument driver with their Windmill
4. 3 software suite. For the free data
acquisition software, go to www.
windmill.co.uk/jsarrdms.htm. They
also have a newsletter that is worth
subscribing to.
Steve Lueck
Bisbee, AZ
