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Defeating the mantis part 3

Just made a small mod to one of the PAL camera module, so I can have it genlock remotely. Wanted absolute minimum modification to the camera module:

camera module external circuit cable ............................ . -------------------------------------------------< +5V . | . | . | . | ------ 17 MHz xtal . R 3k9 | A |--|[]|--- 22p . | 100k (optional) | S | |-----||-------------- R -- > I | | . | | | C |--------- . c NPN | 1M | | . b------- R ----< control voltage ------ . e . | | . | BFR91 . | -------------------------------------------------o GND . | . . ----------------------------------------------------> Composite video .............................

The 22 pF goes inside the camera: ftp://panteltje.com/pub//PAL_camera_internal_genlock_mod_img_1594.jpg

An extra hole creates a third connection: ftp://panteltje.com/pub//PAL_camera_mod_extra_external_connecton_img_1598.jpg

And the crystal tuning circuit goes on the back: ftp://panteltje.com/pub/PAL_camera_freq_control_img_1600.jpg Note that I left out the collector - base resistor, maybe not needed, I get exact sync at about 1.1 V control voltage with this one. That resistor would improve linearity.

It is a nice method to control a crystal oscillator. The Cce of the BFR91 is specified .3 pF at 10 V Vce, and increases big time when collector voltage drops.

With this configuration the camera can be far from the control logic, as the control voltage is near DC.

Found a LM1881 in the box, these chips are no longer made it seems, Will likely use it in one channel, and a discrete sync separator, perhaps like this one

formatting link
in the other channel.

The LM1881 already has an odd / even frame output, so that can directly drive a HC4053 CMOS switch to select one or the other camera each frame. Then the other parts of the HC4053 can be used for the H and V comparators. Will have to look for some piece of veroboard to solder it all together,

Reply to
Jan Panteltje
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when collector voltage drops.

control voltage is near DC.

this one

a HC4053 CMOS switch to select

Might want to consider a wee 100pF cap across BE of the BFR91 so it doesn't go berserk. Sometimes RF transistors can do that while innocently continuing to work at low frequency.

--
Regards, Joerg

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Reply to
Joerg

On a sunny day (Mon, 28 Sep 2009 12:54:20 -0700) it happened Joerg wrote in :

Yes, I am planning on some 78L05 regulators and 10 uF + 100 nF per camera too. An other one I use has about 15 meters cable with a 7805 on the other end. Uses a few wires in the ethernet cable.. 12V in on this end. Not exactly 75 Ohm, put works perfectly.

Reply to
Jan Panteltje

camera too.

end.

You might want to consider the existing Power-over-Ethernet standard.

Reply to
JosephKK

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