Message 25773 in TECH.WW
From: G8MNY
Date: Sun, 12 Jul 26 09:29:00 Z
Newsgroups: TECH.WW
Subject: Logic Probe
Message-ID: <64746_GB7CIP>
Path: N2MH4|GB7BED|GB7COW|GB7CIP
R:260712/0932Z 33616@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260712/0932Z 14207@GB7BED.#21.GBR.EU LinBPQ6.0.25
R:260712/0928Z @:GB7COW.#44.GBR.EU #:44672 [Hartland] $:64746_GB7CIP
R:260712/0929Z @:GB7CIP.#32.GBR.EURO #:64746 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Feb 07)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Although you can buy a commercial probe, here is one I designed to fit a probe
case I had.
Specification.
Supply 0V & +5V @ 10mA to 0V & +12V @ 25mA
Input Z > 15k
Logic 0 range 0V to 1V
Logic 1 range Supply to Supply less 1V
Single full level pulse detection > 10MHz.
Circuit Description.
Both power rail transistors T1 & T2 are normally on, shorting out the HI &
LOW indicating LED, unless the probe is within 1V of ground or the +ve rail.
When that occurs one of the shorting transistor across the LED is tuned off &
the appropriate logic 1 or 0 LED lights.
Pulses of Logic 0 from T2 feed through the 10nF cap to diode detector to turn
on T4 with the pulses. T4 discharges a 4u7 Cap to hold on the pulse indicator
LED. Pulses only of logic 1 from T1 do the same for TR3, which turns on T4 to
light the LED as before.
LED STATUS
Condition Hi LED Low LED Pulse LED
HIGH ON OFF OFF
LOW OFF ON OFF
HI/LOW 1:1 ON ON ON
HI/LOW 1:50 DIM ON ON
HI/LOW 50:1 ON DIM ON
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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