Sync separator LM1881

powerbvd · Apr 29, 2005

Just got LM1881 from Jameco.
According to the doc, the pinout:

1 composite sync output
2 composite video input
3 vertical sync output
4 ground
5 burst/back porch output
6 Rset
7 odd/even output
8 vcc (5v-12v)

Sorry for being stupid, how exactly do I wire this IC
in the supergun(with NeoBitz installed)? Do I connect
sync signal from JAMMA to pin 2 and bring pin 1
to NeoBitz as the sync input? What about the other
pins?

dogtoy · Apr 29, 2005

powerbvd said:
Just got LM1881 from Jameco.
According to the doc, the pinout:

1 composite sync output
2 composite video input
3 vertical sync output
4 ground
5 burst/back porch output
6 Rset
7 odd/even output
8 vcc (5v-12v)

Sorry for being stupid, how exactly do I wire this IC
in the supergun(with NeoBitz installed)? Do I connect
sync signal from JAMMA to pin 2 and bring pin 1
to NeoBitz as the sync input? What about the other
pins?

pin 2 is where sync from jamma goes
pin 3 in V-sync output

the lm1881 does not actually output H-sync, but you can get H-sync by using two gates on the composite sync output line (pin 1) as described here:

http://www.epanorama.net/documents/vga2rgb/vgamonitor.html

You will also need the resistors, caps, whatever is recommended in the datasheet.

cheers,
-DT

Dean · Apr 30, 2005

You will pull the sync output from Pin 1 for use with the NeoBitz. You need to put a 0.1 uF cap and 680k metal film resistor in parallel between pins 4 and 6. The composite video input should be input to pin #2 using a 0.1 uF cap on the line. And make sure to wire ground and +5V

Pins 3,5, and 7 are not used.

Most importantly, you should note that sometimes you don't want the NeoBitz receiving filtered sync from this chip. Hence you need an SPDT switch in line to allow for switching between these.

powerbvd · Apr 30, 2005

D-Lite said:
You will pull the sync output from Pin 1 for use with the NeoBitz. You need to put a 0.1 uF cap and 680k metal film resistor in parallel between pins 4 and 6. The composite video input should be input to pin #2 using a 0.1 uF cap on the line. And make sure to wire ground and +5V

Pins 3,5, and 7 are not used.

Most importantly, you should note that sometimes you don't want the NeoBitz receiving filtered sync from this chip. Hence you need an SPDT switch in line to allow for switching between these.

Thanks for the killer instruction!! You rock!!

JMKurtz · Apr 30, 2005

www.gamesx.com has a nice article on using the LM1881:

http://www.gamesx.com/misctech/lm1881.htm

dogtoy · Apr 30, 2005

D-Lite said:
You will pull the sync output from Pin 1 for use with the NeoBitz. You need to put a 0.1 uF cap and 680k metal film resistor in parallel between pins 4 and 6. The composite video input should be input to pin #2 using a 0.1 uF cap on the line. And make sure to wire ground and +5V

Pins 3,5, and 7 are not used.

Most importantly, you should note that sometimes you don't want the NeoBitz receiving filtered sync from this chip. Hence you need an SPDT switch in line to allow for switching between these.

So the only point of using the lm1881 with the neobitz is to filter the sync line and not to actually separate horizontal and vertical sync?

-DT

Dean · Apr 30, 2005

dogtoy said:
So the only point of using the lm1881 with the neobitz is to filter the sync line and not to actually separate horizontal and vertical sync?

-DT

Yep.

dogtoy · May 1, 2005

D-Lite said:
Yep.

Makes more sense...I was wondering why the neobitz would require separate sync. :kekeke:

Juan ninten 369 · Dec 18, 2010

amm, I have a question :spock:

.
I'm doing an encoder based on the CXA1645, but so far I've managed to look good :confused:

.

This chip can solve the problem? :spock:

jew90 · Dec 18, 2010

I'm not too much of a fan of the LM1881 anymore.

It can strip a compostie video to composite sync fairly well (you can also get a c-sync / fake h-sync by using gates as described above) which works with most all but picky monitors.

The Elantec EL4583 is a much better soltuions.

£8 instead of £2.50 but won't have any problems with it.

http://www.intersil.com/products/deviceinfo.asp?pn=EL4583

I used one on one of my cabs that I has a retrofitted 'scart' socket on their for RGB consoles / DVD's etc.

The monitor wouldn't work with the LM1881 as it needs true H/V sync to operate.

Might be worth looking into depending on what you need

If it is just simple job then the LM1881 might be just what you need though

FusionITR · Dec 20, 2010

jew90 said:
EL4583 is a much better soltuions.

When I saw this post I was like "cool there is a sync separator that outputs HV sync directly unlike the LM1881"

Then I look up the price on digikey (don't know how £ converts).

:eek:

$10.50 for this IC :eek:

Damn I thought I found a good replacement for the LM1881 but not at that price

Xian Xi · Dec 20, 2010

Well if it does the job...

jew90 · Dec 20, 2010

FusionITR said:
When I saw this post I was like "cool there is a sync separator that outputs HV sync directly unlike the LM1881"

Then I look up the price on digikey (don't know how £ converts).

$10.50 for this IC

Damn I thought I found a good replacement for the LM1881 but not at that price

Yes.. unfortuantly it is like 3x the price but it is worth it, especially if you need it. I've had no problem driving picky monitors with it, plus you dont' need extra logic to do things unlike the LM1881N.

But if you can get away with using cheaper IC and sure you wont need proper HV sync then no point spending extra money...

Juan ninten 369 · Dec 21, 2010

ok, thanks for the info, but they only need to filter the synchronism of neo geo board, as the CXA1645 starts doing weird things like jumps and image distortion :confused:

.

if the LM1881 can filter the appropriate signal to the CXA1645 is what Need to Know :conf:

.

a greeting.

jew90 · Dec 22, 2010

Juan ninten 369 said:
ok, thanks for the info, but they only need to filter the synchronism of neo geo board, as the CXA1645 starts doing weird things like jumps and image distortion .

if the LM1881 can filter the appropriate signal to the CXA1645 is what Need to Know .

a greeting.

Are you using the CXA1645 to turn RGB into Composite Video?

If so it only takes upto 1vpp max on the RGB lines.. the Neo outputs much higher than this which could cause issues.

http://www.gamesx.com/rgbadd/cxa1645.pdf

Have you read the data-sheet?

Be sure to read the notes at the bottom, it also has some in-circuit examples.

Be sure that analog RGB signals are input at
1.0Vp-p maximum and have low enough
impedance. High impedance may affect color
saturation, hue, etc. Inputting RGB signals in
excess of 1.3Vp-p may disable the clamp
operation.

SC and SYNC input pulses
Attach a resistor and a capacitor to eliminate highfrequency
components of SC (Figure A) and SYNC
(Figure B) before input.

Juan ninten 369 · Dec 22, 2010

then, is not possible to convert the RGB to composite video with this IC? :confused:

was aware of the problem but do not have any other IC that makes this operation.

Any ideas to solve the problem or just can not. :confused:

jew90 · Dec 22, 2010

The CX1645A should convert the NEO GEO RGB + Sync into compostie video.

You will need some resistors on the RGB line to drop the voltage down as the chip only takes upto 1.0vpp on RGB lines but the NeoGeo outputs higher (2vpp) on RGB.

Probably need resistor on sync line too.

Otherwise chip will not work properly

You should NOT need the LM1881N...

Juan ninten 369 · Dec 23, 2010

ok, ok, thank you very much :glee:

.
I'm glad not to have to use another IC :rolleyes:

.
I'm going to get variable resistors in the input lines and complete the circuit for high frequencies.

Thank you very much again :tickled:

.

Sync separator LM1881

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