Subject: Hold Function for Radio Shack Frequency Counter (Did It!)
From: galen@picea.CFNR.ColoState.EDU (Galen Watts)


How to add a hold function to the Radio Shack RF Frequency Counter:

Ground TP17.  In the schematic, TP17 is pin one of U3, connected to
+5V thru a 47k resistor.  On the circuit board, TP17 is on the display
side, just right of the lower-right corner of the IC.  Grounds are about
1/4 inch below and to the right, the three non-tinned points in the large
area of metal.

I grounded TP17 directly and the display stopped.  After lifting the ground,
the counter resumed counting at the beginning of a sampling cycle.

Personally, I would ground TP17 thru a 1k resistor.  I haven't performed
the mod to my RS counter, since the pads are VERY small and my fine-tip
iron is at work.  I will try the 1k Hold mod on Monday and give a report
(unless somebody beats me to it).

An amplifier mod to increase the sensitivity is in the works, reports to follow.

Happy Trails to You,
Galen, KF0YJ


Newsgroups: sci.electronics,rec.radio.amateur.misc,rec.radio.scanner,rec.radio.amateur.equipment,rec.radio.amateur.homebrew
From: galen@picea.CFNR.ColoState.EDU (Galen Watts)
Subject: RS FREQ COUNTER HOLD MOD!!!!!!!!!
Sender: news@yuma.ACNS.ColoState.EDU (News Account)
Message-ID: <Nov15.191532.82222@yuma.ACNS.ColoState.EDU>
Date: Mon, 15 Nov 1993 19:15:32 GMT
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Organization: College of Natural Resources, Colo. State Univ.
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How to add a hold function to the Radio Shack RF Frequency Counter:

Ground TP 17.  In the schematic, TP17 is pin one of U3, connected to
+5V thru a 47k resistor.  On the circuit board, TP17 is on the display
side, just right of the lower-right corner of the IC.  Grounds are about
1/4 inch below and to the right, the three non-tinned points in the large
area of metal.  TP17 is the tinned pad next to a SM resistor marked '473'
for 47k.

I rigged a momentary switch to ground TP17 thru a 1k resistor (you never
can tell) and it works just fine!  I drilled a small hole to mount the switch
just above the plastic depression so I could push the button with my right
thumb.  A small toggle switch would fit.

I'll be trying the other TP's to see what wonderful things RS didn't put
on the front.

Galen, KF0YJ