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Thread: 4 digit auto-ranging frequency-meter.
www.piclist.com/techref/index.htm?key=digit+auto+ranging
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face BY : Regulus Berdin email (remove spam text)



Octavio Nogueira wrote:
>
> >The posted circuit is incomplete, for a more sensitive frequency
> >counter, it needs a pre-amplifier and convert its output to TTL level.
>
> Does anyone have a nice and simple pre-amplifier schematic for this kind
> of application?

I'll try on ascii:

                      +---------+---O +5V
                      |         |
                     3K3       1K
                    ohms      ohms
                      |         |
                  +---+         +-----+
                 +|   |         |    +|
            2.2uF =  10K       820    = 2.2uF
                  |  ohms      ohms   |
                 GND  |         |    GND
                      |         |                  OUT
                      |         +-----||----+----O TTL
                      |         |    10nF   |
IN  10nF         10nF  |       |/            |
O----||----+--+---||---+-------|   MPSH10   10K    adjust for DC
          |  |        |       |\           Ohms   level be in the
  1N4148  V  -       3K3        v         trimmer middle of TTL
    X2    -  ^       ohms       |           |     thresholds
          |  |        |         +----+      |
        GND GND      GND        |    |     GND
                               120   |+
                               ohms  = 10nF + 2.2 uF in parallel
                                |    |
                               GND  GND


This circuit could work from to 0.02-50 MHz.

Reggie

<361C051C.8FB57787@skyinet.net> 7bit

See also: www.piclist.com/techref/index.htm?key=digit+auto+ranging
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