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G8MNY > TECH 09.07.04 22:22l 45 Lines 1818 Bytes #999 (0) @ WW
BID : 462_GB7CIP
Read: GUEST OE7FMI
Subj: Logic Probe
Path: DB0FHN<DB0FOR<DB0SIF<DB0GV<DB0LJ<DB0RES<ON0AR<IK1ZNW<GB7CRV<GB7CIP
Sent: 040709/1808Z @:GB7CIP.#32.GBR.EU #:462 [Caterham] $:462_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Correction Mar 04)
Although you can buy a commercial probe here is one I designed to fit a probe
case I had.
Specification.
Supply 0 & +5V @ 10mA to 0 & +12V @ 25mA
Input Z > 15K
Logic 0 0v to 1V
Logic 1 Supply less 1V
Single full level pulse detection >10MHz.
T1 PNPÚÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄ +ve
³/e _³_HI _³_ ³ ³ ³
ÚÄÄ´<ÃÄÄ´ \ /LED /_\ ³ 390 ³
³ ³\ ÄÂÄ ³ ³/e ³ ³
³ ÃÄÄÁÄÄ´ÃÄÄÄÁÄÄÄ´ T3 _³_PULSE ³
27K ³ 10n ³\ PNP \ /LED ³
³ ³ ³ ÄÂÄ ³+
Probe <ÄÄÄ´ 390 100K ³ ===
³ ³ ³ ÚÄÄÄ´ ³ 10u
27K ³ 10n ³ ³/ ³ ³
³ ÃÄÄÂÄÄ´ÃÄÄÄÂÄÄÄÄÄÁÄÄ´ ³+ ³
³ ³/ _³_ _³_ T4 ³\e === ³
ÀÄÄ´>ÃÄÄ´ \ /LOW /_\ NPN ³ ³4u7 ³
³\e ÄÂÄLED ³ ³ ³ ³
T2 NPN ÀÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄ -ve
Circuit Description.
Both power rail transistors TR1 & TR2 are normally on, shorting out the HI &
LOW indicating LED unless the probe is within 1V of ground or +ve rail. When
that occurs the shorting transistor across the LED is tuned off & the
appropriate logic 1 or 0 LED lights.
Pulses of Logic 0 from TR2 feed through the 10nF cap to diode detector to turn
on T4 with the pulses. TR4 discharges a 4u7 Cap to hold on the pulse indicator
LED. Pulses only of logic 1 from TR1 do the same for TR3, which turns on T4 to
light the LED as before.
/QSL
73 de John G8MNY @ GB7CIP
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