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- I named this "TS-AVSPU-001E" -
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This pizzabox sized device was my solution to a need for more versatile video inputs as well as to easily switch between multiple inputs.
I also fancied the idea having rotary knobs to set the picture up with a nifty middle mark for the neutral position.
I took inspiration from classic HiFi equipment with AC outlets, my dad had a Sony HiFi setup in the living room with the tuner unit passing power to the other units with europlug sockets on the back.
That's why there's a chunky power button on the front to power an CRT TV.
The purpose here is mainly about to convert S-Video to RGB but it goes way beyond that by also converting composite to RGB and even RGB to RGB by using the "fast blanking input" on the scart inputs. And this contraption
also supports NTSC as well and by having an pure RGB output means it's easy to horizontally shift the picture around by processing the extracted sync signal with three NE556 chips (2x NE555 timers in a package each).
With this device there's no need to mod the TV for S-Video input or NTSC support, both features absent on the majority of 14-20 inch Trinitron TVs with a single RGB SCART input.
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A TDA8361 with it's breadboard unfriendly 1,778mm pin pitch runs the entire show that does all the video processing, three AD810 video op amps drive the RGB outputs, the iconic LM358 is used as audio amplifier, some CMOS logic, switches and comperators are used for certain tasks and all that
is powered by an internal 12V wallwart and two linear regulators (classic 7808 and 7805 in TO-220 package) that are bolted to the bottom metal plate.
And if you can believe it: There's a fuse hidden in that wire nest.
Very hard to see but it's there to protect from overcurrent.
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The front features an Horizontal Shift control with a ridiculous wide range, that the picture can wrap around to the other side. There's also a detection circuit that senses if the RGB input is permanently enabled, in that case the relays switch extra resistance to perfectly compensate for common left-shift many RGB monitors have.
The Brightness, Contrast, Saturation and Tint work in the same manner as they do in "old" TVs from the time when remote controls weren't an standard inclusion. Also the sharpness control is set internally to good looking value to display composite with decent detail and minimal ringing.
The inputs are selected with simple switches in the binary system, the audio input can be independently selected from the video input.
The output 2 "switch enable" button activates the (high current) 12V output to the 2nd scart output, this can be used to drive external relays on the scart cable. The blank screen button simply shuts off the RGB drivers, this is quite handy to quickly check the black level on the TV.
The back has all the connectors.
The AC input goes first to the powerswitch then to the AC output and power supply, which also lights up the three LEDs at the same brightness to indicate all voltage rails. The remote connector is able to override all controls on the front with the exception of the the pushbuttons, these are paralleled.
The usual AV connectors are outputs that work as expected.
The biggest connector is the key element to keep the main unit small and compact. All inputs are feed through external multiplexers, this interface is designed to select from 16 AV inputs, the supply voltage is not fixed but in this case it's 8V for VDD and VSS,VEE are tied to ground.
Originally I've "mounted" a 2x20 box header with locking tabs for this, but I wasn't really satisfied with that connector as the hotglue kept on breaking off. So in 2024 after 9 years of daily use, that crappy pin header was replaced with a big bulky D-Sub 37 connector. Which explains the little gap to the left.
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The white KV-M1420 was first paired up with this.
My design choice of white case with black front fits very well with that set.
But in 2020 I saw an local offer for the slightly bigger KV-M16, so the smaller TV was moved into storage.
The last thing I've planned is to replace these sloppy paper labels on the back with better transparent ones printed with a proper label printer.
- The AV-MULTIPLEX16 pinout-
1=Red
2=Green
3=Blue
4=VideoSel0
5=Y/C switch (OC, pulldown to enable)
6=VidelSel2
7=Spare input 1
8=Left Audio
9=Right Audio
10=AudioSel0
11=Fast Blanking (SCART RGB enable)
12=AudioSel2
13=SCART AV switching voltage (not used and connected in this, voltage divider 50%)
14=CVBS
15=Spare input 2
16=VSS
17,18,19=VCC
~~~
20,21=VEE
22=VSS
23=Spare input 2 return
24=CVBS return
25=AV switching voltage return
26=AudioSel3
27=Fast Blanking return
28=AudioSel1
29=Right Audio return
30=Left Audio return
31=Spare input 1 return
32=VideoSel3
33=Y/C switch return
34=VideoSel1
35=Blue return
36=Green return
37=Red return
All return pins are expected to be ground/VSS.
The actual used CMOS switching ICs limit the supply voltage, always consult the correct datasheet for this.
All signal inputs are properly terminated (my standard for Audio is 15Kohms) and are AC coupled to the CMOS switches, usually 47nF for Video and 470nF for audio.
The AV switching voltage could be up to 13V (even 15V if the AV device is crappy enough), a voltage divider and clamping diodes must be used for protection.
One last thing to mention is the phase 1 filter network consisting of one resistor and two capacitors.
The datasheet of the TDA836x (and the I2C controlled relative TDA884x) don't mention what values to use but all actual TV schematics I've seen had the same values.
I personally recommend 680K instead of 100K, the picture over CVBS/S-Video sometimes flickered weirdly with the lower resistance.
