Building an AV switchbox - electronic or analogue switching?

Construction finished!

On to software debugging.

 

Great to see it taking shape! Have you had a chance to test yet to see if you're getting any ghosting or noise on your image? That's the bit I'm paranoid about!!

 

Of course I have!

Composite sources are, well, composite, they look crap regardless, and they look no worse when going through the switch than direct to the monitor. I only have two consoles that rely on composite though, and that's the 2600 and the NES. Everything else is RGB or S-Video.

RGB I haven't been able to test yet, because my PVM doesn't accept composite video as a sync source. I need to build a sync stripper, doing that tomorrow.

What I was able to do was test my PS2 with Y/Pb/Pr Component video, and it looks absolutely immaculate. Played Kingdom Hearts with the PS2 connected directly for about 10 minutes, then swapped over to going via the box, and noticed no difference whatsoever.

 

Coming on nicely indeed.

You say your "PVM doesn't accept composite video as a sync source. I need to build a sync stripper, doing that tomorrow." - have you given pin 16 between 1-3v to tell it to work in RGB mode? C-Sync can be gained normally from C-Sync, or composite, or luma.

 

The Sony PVM's don't use SCART, they have 5 BNC connectors for R, G, B, C-sync/H-sync, and V-sync:



On the switch box, SCART pin 20 from the selected input goes to a BNC output on the box, then to the C-sync/H-sync input on the monitor. The wiring is correct, it's just that the monitor can't use composite video as a sync source. The picture appears scrambled.

The alternative to adding a sync-stripper would be to modify all my cables to pick up the C-sync signal from the consoles instead of the composite video signal, but that would be a lot of very fiddly work, particularly on the MD2 and Saturn cables. Eugh, no thanks!

Update: Built the basic LM1881 circuit as per the datasheet, and my switchbox is now perfectly complete!

 

Beautiful!! I want more pics XD

 

hold on a second, can those things take Y,PB,PR then? 'Cause it totally says that... why didn't I know this?

 

They do take component, but only up to 480i, well at least mine does. I've heard some of the PVM's in the UK take SCART.

 

Have a look: http://www.youtube.com/watch?v=AH5M4Xj5-RY

 

Just had a look and I've got to say, that UI is very snazzy looking.
One day I'll have more than a Sega Mega Drive / CD / 32X, Saturn and Dreamcast to hook in.
When that day comes, I'll probably follow along your path! :victorious:

 

That switch really does look amazing mate!! I need to get off my arse and finish my schematic, which will then let me hit up the layout functions in Eagle to progress it further and get a full parts list so I can start shopping.

I'll have to stop getting distracted with other things - have recently installed an s-video amp in my A2600, added a stealth chip to my PSone and installed a SuperCIC in my SNES. Oh, and I've started servicing my old betamax player

... so I think it's not just laziness, but it's getting distracted by projects easier to complete that's compounding the switchbox's progress for me XD

 

Hahaha, distractions... I think that's the problem of a lot of us on here. Getting distracted by other projects is so easy!
I had Sophia in pieces for well over 6 months and two Mega Drives that were 60Hz / Language modded just collecting dust for at least 9 months.
Needless to say I eventually got the drill and put holes in the case... that's all I needed to do!
But there were just always other things to do. Always! :biggrin-new:

 

Heh, I recently had to put my "to do" pile into ten 80 litre storage boxes and put them into storage! Well, some of it, at least! There's still a Betamax machine (or ten) scattered around the place in hundreds of pieces, too!

 

How did it come down to this. I am determined to recap that Sophia with the caps that did decide to turn up today.
Who knows, maybe one day it will be attached to a giant AV switch box like this one!

 

So, MangledLeg, gotten further with yours? Keen to see it!

 

Slowly making progress on the switch - was going to spend some time last weekend on it but ended up getting distracted by being a good husband and getting some stuff done around the house then selling some crap off on eBay. Might put in a little time tonight to keep going - need to make a component in Eagle for the 74HC174 and then continue working on the schematic. Shouldn't be too tricky, but my original schematic was a bit arse, and while the new one is still chunky, it will be a bit better than my original one I hope!!

Mind, once it's done then the real fun begins - I'm a little scared about what my shopping list for parts is going to look like

Have you been enjoying your switchbox?

 

Immensely. It's deeply satisfying having every console at my fingertips.

 

Potentially daft question on 14 segment displays. Since I'm not clever enough to know how to interface these with a microcontroller I'm thinking of how to proceed. I have a 4-way rotary switch in my current design that delivers power (+5v) to each family of inputs. What I'm thinking is that each input will send the +5v to the corresponding legs of the 14 segment displays to make the characters appear. I've seen the same thing done on a 7 segment display when you aren't being clever and using a simple driver IC + counter setup (which is what mine's based on).

So I'm trying to work out how to get the 14 segment display going. It's messy, but would directly feeding the appropriate legs for each module off the +5v by using something like:

+5v-----[NPN transistor]-----[Resistor]-----[Leg of 14 segment display]

, with the above repeated for each leg? This would mean 16 transistors per leg which seems a bit silly.

Alternatively, could a driver IC by used in a dumb mode - feed +5v to a driver IC (like a A6282) without any logic and wire up the regulated outputs directly to each component? I guess even doing it this way would be overkill because the lack of microcontroller logic (i.e. using it as a dumb amplifier) would mean one of those ICs for each display segment per family of inputs...

The other option might be to use a double pole rotary switch so that with each switch +5v goes to the ICs powering the relays and the other pole contains GNDs for the 14 segment displays, and use a common powered 14 segment display that turns LEDs on by virtue of the LED have a GND to complete the circuit.

This would still be messy compared to a microcontroller solution (this will still require each display segment's LED pins to have a 4-input bus to cater for the four family of inputs), but it would be cleaner than powering everything using +5v and regulating the feed so the LEDs behind the 14 segment displays...

Damn microcontrollers and my lack of understanding them

 

The obvious approach is to use diodes - just take each +5V supply and feed it via diodes to the anodes of the segments you want to light up (assuming this is a common cathode display - if it's common anode, then use 4 NPN transistors that switch down to ground and connect the diodes to those.

Edit: Depending on the messages you want to display it might be worth drawing out a truth table and identifying any segments that have common patterns across all the switch states and then just using one set of diodes (but obviously multiple resistors) for each set of common segments. If you find a segment that only activates in one state, then you can even leave the diode out, but you may need to adjust the value of the current limiting resistor because otherwise the current through the LED may be slightly higher due to the lack of the 0.6V drop across the diode.

 

Alright, have decided my brain's not doing a very good job around this. @Trimesh, apologies if I didn't note it but I was talking about using LED 14-segment displays, and driving them would be a bit convoluted.

So, I'm bringing it back to something more basic - I'm looking at whacking in a single 7-segment LED to display "AbCd" and then the input numbers afterwards. So input 1 on composite would display "A.01". Not all that fancy, but something at least.

So now I'm curious to see if there's an equivalent to something like a CD4511 but will drive "AbCdEF" on 7-segment displays using some basic binary logic (i.e. if pins 3 and 4 are set to +5v, the letter "b" is displayed). Does anyone have any ideas? I figured a driver IC would be cleaner than feeding voltages with resistors to the display module