R:190705/0838Z 19755@OK2PEN.SP.BRA.SOAM [Sao Jose dos Campos] $:11326_GB7CIP R:190705/0837Z @:GB7CIP.#32.GBR.EURO #:11326 [Caterham Surrey GBR]

From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW

From: PA3BNX@PI8SHB.#NBO.NLD.EU (New Apr 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Hello All,
Subject: Handsfree ptt-switch for mobile use. ---------------------------------------------------
Using a vox is not nice in a car because it goes transmitting when it hears sounds.

Keeping a ptt switch pressed while driving & stearing is also unsafe.

Thats why I decided to make a large toggle switch on the dashboard with a Red 5mm flashing PTT led & a Mic gain control.

Construction of toggle switch
-----------------------------
I made from double clad PCB about 3 x 6 cm & a microswitch as a nice toggle switch. I did solder a small hange to the PCB& tinned box. And I mounted the microswitch in the metalbox & only the handle pin is pushed when the PCB piece is pushed. I did painted it red hi.
So I have a nice big easy to push PTT switch.

Circuit diagram
---------------
I have made a small metalbox with a large pushbutton (S1) on it.
And a big bright 5mm led.
The pushbutton is connected to a toggle circuit.
The output of the toggle circuit is connected to a watchdog circuit which drives a PTT transistor to switch the tranciever, & also the LED flasher circuit.
Use a 5 mm highbright led so you see it very easy flashing when transmitting without having to look at the tranciever.

So push S1 & PTT is on for maximal 3-5 minutes & the led flashes. After 3-5 minutes the watchdog switches off the mobileset from transmitting.
(use 100-220uF).

So if something happens your rig is not any more transmitting a carrier for hours.

Mount the small box some where on the dashboard next to the steering wheel so you can easy see the led & push the S1 Switch.

Further I mounted a small electreet at the sunscreen for getting the sound.

I also mounted a small mic-preamp with a gain potentiometer in the
ptt switchbox so I can adjust the audio level when driving.

PTT toggleswitch
----------------
100n┌────┬─────1M──┐
=== │S1 │ 10106 or 4093 etc.
│ o │
┌──┤ \ │\ │ │\
_│_ │1n ├──┤ `>o──┴──┤ `>o──┬────>to A
=== │ │/' │/' │
└────┴─────100k──────────┘

Watchdog & led flasher
----------------------
┌───┬──────── +Vcc 9─15V
│ │
A 3M3 _│_ 1N4148
│ │ /_\ ┌───┬────o Ptt
│ _ │ │ _ 4093 BC547 │ │
├─┤ `\ 100u │ │ ┌─┤ `\ │/ _│_
│ │ & )o─1k──┤├─┴───┴─┤ │ & )o─┬─10k─┬──│ /_\
└─┤_,/ + └─┤_,/' │ │ │\ e │ 1N4007
4093 │ 4k7 │ │
Ground────────────────────────)─────┴────┴───┴────o
│
┌─────────────────────────────┘
│ _
└──┤ `\ _ 4093
│ & )o───┤ `\
┌──┤_,/ │ & )o─┬───1k───┐
│ ┌─┤_,/ │+ _│_
1M 100k === 1uF \_/≡ Red 5mm Led.
└─────────┴────────┘ ┴───────Ground

Mic─ampliflier
--------------
2 wire electret.
┌────────┬───────────────────────┬──560──+Vcc 9─15V
│ │ 10uF │+
4k7 22k ===
│ │ 741 or LF353 _│_
│ ├─────┬─┤\ + 10uF
│ u1 │100p===│±`>o─┬─┤├─┐
│()─┬┴─┤├─4k7─)───┬─┴─┤/' │ │
│ === +┌──┤ │ │ 5k
│ │1nF === │ └─47k─────┘ pot<──o Rig Mic
│ │ 10u│ 22k │
└──┴──────┴──┴──────────────────┴────o

Gain = about 10x

I did not wrote the pin numbers of the ic's to it yet.

73's from PA3BNX@PI8SHB.


Y don't U send an interesting bul?

73 de G8MNY @ GB7CIP

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