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G8MNY > TECH 24.01.26 19:08l 87 Lines 4326 Bytes #6 (0) @ WW
BID : 50345_GB7CIP
Subj: Eagle DB120 Sound Meter
Path: JH4XSY<N3HYM<IW2OHX<GB7CIP
Sent: 260124/1003Z @:GB7CIP.#32.GBR.EURO #:50345 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Correction Feb 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
The is a simple cheap sound meter.
____ PCB LAYOUT
ﾚﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳｳ~~~~~~~~~~ｳｳ ｳ /~~~\ ｳ
ｳｳ \ ｳｳ ｳQ12ｳMETERｳVR2ｳ
ｳｳ \ ｳｳ ｳ \___/ ｳ
ｳｳ__________ｳｳ 40dBA-120dBA in 2 ranges ｳ ｳ
ｳ ____ｳ In built calibrator ｳVR1 __ ｳ
ｳ /~~\ ｳ ｳﾚｿ Q5 /~ ~\ｳ
ｳ ｳ ｳｳ ｳｳｳ ｳSWITCHｳ
ｳ \__/ ｳ ｳｳｳIC \_ _/ｳ
ｳ ~~~~ｳ ｳﾀﾙ VR3 ~~ ｳ
ｳ ｳ ｳ ｳ
ｳ EAGLE ｳ ﾀｿ ﾚﾄﾄﾄｿ ﾚﾙ
ｳ ｳ ｳVR5ｳ ｳVR4ｳ
ｳ ｳ ﾀﾄﾄﾄﾙ ﾀﾄﾄﾄﾙ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
CIRCUIT
ﾚﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾄ2K2ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄ<+ve
ｳ 56K ｳ ｳ ｳ ｳ OPAMP
ｳ + ｳ ｳ/ ｳ+ ｳ ｳ The TD7120 provides
MicﾄｴﾃﾄﾅﾄｴQ3 === ｳ 56K fixed stable gain
ｳ 4u7 ｳ ｳ\e ｳ33u 7ｳ ﾚﾄﾄﾄｿ ｳ to drive the non the
ｳ 56K ｳ ｳ Low 2ｳ~\ｳ3 56K ｳ linear metering stage.
ｳ ｳ VR2ﾃﾄ)ﾄﾂﾄﾄﾄﾄﾄﾄﾄo<ﾄ2K2ﾄﾄﾂﾄﾄﾄｴTA\ 6ｳ ｳ +
ｳ ｳ Mic ｳ14K4 150K ｳ7120>ﾄﾁﾄﾄﾄﾄ)ﾄﾄｴﾃﾄﾄ3K3ﾄ>
ｳ ｳ cal ｳ ﾃﾄﾄﾄﾄﾄﾄﾄo ﾃﾄﾄﾄｴ /ﾀﾄﾂﾄ19Kﾄｴ+ 10u
ｳ ｳ ｳ ｳ220R High +ｳ 5ｳ_/ 1 ｳ ===
ｳ ｳ ｳ ｳ ｳ 10u=== ｳ4 ===3n3 ｳ10u
ﾀﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾂﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄ<
ﾀﾄﾄVR1ﾄﾄﾂo Cal
200R ｳ ﾚﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄ5K1ﾄﾄ<+ve
220K ｳ 33K 33K ｳ
PREAMPS ｳ 3K9 ｳ ｳ 3K9
The 3 wire electret mic ﾀﾄﾄﾄﾄﾅﾄﾄｴﾃﾁ\ /ﾁｴﾃﾄﾄｴ
& preamp Q3 is powered \ｳ X ｳ/
from a decoupled rail. Q2ﾃﾄﾄﾄﾙ ﾀﾄﾄﾄｴQ1
e/ｳ ASTABLE ｳ\e
VR2 calibrates the mic ﾀﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾙ
capsule & VR1 calibrates 100R
the astable calibrate ﾄﾄﾁﾄﾄﾄ<
oscillator Q1&2.
METER DRIVER oOff
+ve<ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄｿe ﾚﾄﾄﾂﾄﾄﾂﾄo<ﾄﾄﾄﾂﾄﾄｿ
10K ｳ/ 47uｳ+ \ / 2K2 ﾃﾄoHighｳ ｳ
ﾃﾄﾄｴQ5 === ﾄﾄﾂﾄﾄ ｳ ﾀﾄoCal ｳ ｳ
_ｳ_ ｳ\e +10u ｳ Q7ﾃﾄﾄﾄﾄﾙ ﾚﾄoBat ｳ ｳ
\_/ ﾃﾄﾄﾄ560Rﾄﾄﾂﾄｴﾃﾄﾄﾂﾄﾄﾄｿ ｳ ｳ ｳ oOffｳ ｳ
_ｳ_ ﾃﾄﾄｿ +ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ
D1 \_/ ｳ/e ｳ ===10u ｳ ｳ ｳ _ｳ_ ｳ ｳ ｳ
ﾚﾄｴ>ﾃﾄｿ ﾃﾄﾄｴQ6 100K ｳ ｳ ｳ ｳ /_\' ｳ === ｳ+
ｳ ｳ ｳ/ ｳ\ ｳ ﾚﾄﾁﾄｿ ｳ ｳ ｳ ｳ ｳ ｳ BATT
>ﾄﾅﾄ2K2ﾄﾅﾄﾄﾂﾄﾄﾄｴQ4 ｳ ｳ _ｳ_ _ｳ_ _ｳ_ _ｳ_ ｳ ｳ ｳ ｳ PP3
ｳ ｳ 100k ｳ\e ｳ ｳ \_/ /_\ \_/ /_\ ｳ ｳ ﾄﾄｿ ｳ ｳ
ﾀﾄｴ<ﾃﾄｴ ﾀﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄ)ﾄﾄｴ+ ｳD9 ｳD8 ｳD7 ｳD6ｳ ｳ VR3 680Rｳ ｳ
D2 ｳ 220R ｳ === ｳ ｳ ｳ ｳ ｳ ｳ 50K ｳ ｳ ｳ
ｳ ｳ ｳ ｳ10u ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ ｳ
<ﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾂﾄﾁﾄﾄﾄﾄﾁﾂﾄﾁﾄﾄﾄﾄ)ﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄ)ﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾁﾄﾄﾁﾄﾄﾙ
ｳ 10u=== ===10u ｳ ｳ ｳ
D3ﾃﾄｴ<ﾃﾄﾄﾁﾄﾄVR5ﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄｴ>ﾃﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄｴ
ｳ 5K D10 ｳ VR4 33u=== Meter
D4ﾀﾄｴ>ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄ2Kﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾙ
To get a usable 40dB scale on a meter quite a lot of compression is needed.
This circuit uses an AGC approach. Transistors Q4, 5 & 6 from a power amp to
drive the double voltage doubler bridge D6-10 rectified load of the meter &
also provide AGC with D3 & D4 making an variable input attenuator.
VR5 set the AGC log action & diodes D1 & D2 correct for over compression to get
the very linear 40dB scale. VR4 is the main calibrate & VR3 is the battery cal.
See my bul on "Sound Levels dBA dBB dBC".
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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