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G8MNY > TECH 30.12.05 12:20l 46 Lines 1883 Bytes #999 (0) @ WW
BID : 10992_GB7CIP
Read: DL1LCA GUEST OE7FMI
Subj: Logic Probe
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<GB7CIP
Sent: 051230/0102Z @:GB7CIP.#32.GBR.EU #:10992 [Caterham] $:10992_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Nov 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 PNP ÚÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄ< +ve
³/e _³_ HI _³_ ³ ³ ³
ÚÄÄ´<ÃÄÄ´ \_/>LED /_\ ³ 390 ³
³ ³\ ³ > ³ ³/e ³ ³
³ ÃÄÄÄÁÄÄÄÄ´ÃÄÄÁÄÄÄ´ T3 _³_PULSE ³
27K ³ 10n ³\ PNP \_/>LED ³
³ ³ ³ ³ > ³+
Probe <ÄÄÄ´ 390 100K ³ ===
³ ³ ³ ÚÄÄÄ´ ³ 10u
27K ³ 10n ³ ³/ ³ ³
³ ÃÄÄÄÂÄÄÄÄ´ÃÄÄÂÄÄÄÄÄÁÄÄ´ ³+ ³
³ ³/ _³_ _³_ T4 ³\e === ³
ÀÄÄ´>ÃÄÄ´ \_/>LOW /_\ NPN ³ ³4u7 ³
³\e ³ >LED ³ ³ ³ ³
T2 NPN ÀÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄ< -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.
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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