In article , SWbeginner
writes:

(Avery Fineman) wrote in

There are several LCD display units available commercially with the
LCD (typically 2 x 16 character rows), drivers and temporary
memory, and optional backlights. They are driven by ASCII coded
character digital byte-parallel input assemblies. PIC and Atmel
based counters can output ASCII according to count plus including
controllable legends for whatever purpose, all under the
microcontroller internal program.

I agree with all your points against LED's except they are very simple to
use and that's what I need for now.

Then you can go with LS TTL and use a pair of ICs per decade/digit.
A 74LS192 as a decade's actual counter with a CD4511 as a latch-
decoder-driver for the LED...or a CD40110B as a counter-latch-
decoder-driver at a slower input rate (with prescaler as needed to
reach the desired max. input rate). 74LS90s or 74LS290s as decade
dividers for the timebase...plus various NAND gates to select the
count gate times. All of those types figure in to drive LED 7-segment
numeric displays.

The displays at the aade.com site are very elegant.
If you or someone can recommend which LCD display to use and a site wich a
good tutorial then that would be fantastic.

There's over 50 different models and sizes of LCD display assemblies
available, from 1 line of 12 characters to 4 lines of 16 characters. To
use those assemblies, you need to know how to get the sequential
ASCII into them to show on the screen. That isn't simple for a tutorial
or anything else unless you know serial digital transmission basics.
AADE apparently gets their LCD assemblies in bulk to package with
their little frequency counters, have the necessary coupling from the
16F71 program coding.

The bare LCD unit needs special driver ICs since those are generally
of a sort of 3-state waveform needed to clear/energize (make black)
a selected place. Some are only 2-state. Varies depending on the
type and manufacturer. That's why I recommend getting an assembly
of the display and its driver board. A search of the Internet will turn
up several distributors selling to individuals. If the end applicaion is a
counter using a PIC or Atmel microcontroller, then the project website
will have the part number of the display assembly they used.

The whole point of homebrewing for me is to learn how these things work and
be able to design and make changes. Otherwise I can buy all the gear on
Ebay but not learn anything.

Understood. I'm still putting things together and still learning, still
having
fun with all these new things even though I've been in the electronics and
radio racket for quite a while (over 50 years).

You can get the basics of frequency and period counting from the Agilent
website from one of their application notes. There's several other sites
by individuals explaining basic counting. To make an IC counter using
two ICs per decade, a latch-decoder-driver is needed to hold the binary-
coded-decimal 4-bit state out of the counter after a count and then
decode that BCD to light the appropriate LED segment of a 7-bar segment
single digit display. The whole thing needs a timebase section which
is a crystal oscillator (usally at 10 MHz to beat against WWV for
calibration) followed by dividers (usually decade counter ICs running
continuously. The selectable timebase signals are used to gate the
counter's input for frequency indication with the gate opening time in
increments of 10 such as 1, 10, 100 mS, 1 or 10 Seconds for minimum
count digit display of 1 KHz, 100, 10, 1, and 0.1 Hz respectively. To
mesaure period, just reverse the count input and timebase gate control
so that you count the timebase frequency with the gate supplied by the
input signal.

To connect this to the outside world, you need a wideband amplifier to
help raise the level of the input signal, then a shaper such as a Schmitt
trigger gate or inverter to make the signal have nice, sharp leading edges
to apply to the count gate. With all that digital stuff there needs be
attention paid to bypassing the supply rails, but that is easier since all
the components can be running at the same + supply voltage; +5 VDC
if "74" chips, +9 or +12 or +15 if CMOS equivalent function types to TTL.

There are still lots of digital ICs available for this kind of project and
the
datasheets are all downloadable from the Internet. Putting them all
together is not an easy task but it is repetitious to the degree of the
number of digits to be displayed. The number of digits to be shown will
put a rather surprising large current demand on the supply for a maximum
digit indication, "8" in case of a 7-bar LED, all 7 segments on. 140 mA
per decade at 20 mA per segment. With 6 digits that is 840 mA max.
LED supply drain can go from 240 mA min. for all "1" to 840 mA max. for
"8" with 6 digits...can be fair jump in load change on the internal supply.

In going for a discrete IC per decade style, the overall task is a strenuous
one. To begin, it is much easier to get a KIT if possible, or one of the
little AADE counters (which have some user interconnects necessary).
Once you have it built or installed, you have a "learning" device and can
go back into its guts to find out how it works. For PIC or Atmel based
counters, most "learning" takes place in following the program source
code; the hardware itself is rather simple, just a handful of parts.

A frequency (and period if desired) is the most precision instrument you
can successfully design and build in the home workshop. Only one
circuit, the crystal oscillator, sets the accuracy, typically better than
10 parts per million beat against WWV. The rest is enabled by digital
ICs off-the-shelf at relatively low cost (less than $1 each, average). It
does embrace a number of electronics technologies not necessarily
those of old radio. "Simple" it isn't and that includes the micro-
controller types; those have most digital hardware functions
implemented in software. Experience in designing, building, and
working with them will come in handy on such future projects as PLL
or DDS frequency control, DSP, and many other subsystems of
modern radios. If you bother to study them in detail you WILL learn
a lot of new things, but there is considerable "home work" in that self-
assignment. Good luck and enjoy the course! :-)

Len Anderson
retired (from regular hours) electronic engineer person