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Old Sep 21, 2012, 10:12 PM
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Legot's Avatar
United States, AZ, Gilbert
Joined Nov 2009
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Is there a video comparison of the LM1881 version and the resistor/diode(original) version?

I designed a PCB for the original design that I think is quite nice, but I'd like to know how it would stack up to an lm1881 based board which I admittedly only just learned about. It is actually the 3rd redesign of the board, and I'm finally happy with it. I just want to see if its worth it.
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Old Sep 22, 2012, 12:09 AM
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Henry.'s Avatar
Sweden
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I doupt that there would be are any major differences but i guess it could give a slightly better picture, if at all. The main difference by using the LM1881, which i choosed right away to my pcb when i saw it, is that you dont have to fiddle with anything to get a good picture.
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Old Sep 22, 2012, 07:38 PM
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Quote:
Originally Posted by Ace4 View Post
I had mine working well on a breadboard, so I transferred it to a perfboard. I made the mistake of trying to keep it small, and it isn't working. With the OSD hooked up, the video signal drops to black & white and has some distortion near the top of the screen. There is no text or text background showing up. Any suggestions on what could cause that? I'm guessing there's something on the bottom of the board touching that shouldn't be, but wiggling the wires and components doesn't affect the picture. None of the components themselves are touching each other. I built a voltage regulator into the board for the 5V and one for 3.3V for the GPS, they both appear to be working fine.
I ended up just desoldering all of the wires on the bottom and doing it all over again, and now everything is working great.
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Old Sep 24, 2012, 10:10 AM
Registered User
Latvia, Riga
Joined Jan 2012
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Hi to every one..
Can I use this current sensor?

http://www.ebay.co.uk/itm/ACS712-Mod...item4abc72ca3a

Thanks..
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Old Sep 24, 2012, 10:13 AM
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Denmark, Capital Region of Denmark, Naerum
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Quote:
Originally Posted by walkmanz View Post
Hi to every one..
Can I use this current sensor?

http://www.ebay.co.uk/itm/ACS712-Mod...item4abc72ca3a

Thanks..
I think that should be okay, but it's not the best suited sensor. It's used to measure both positive and negative current. That means large offset and lower resolution.
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Old Sep 24, 2012, 12:31 PM
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Originally Posted by Dennis Frie View Post
I think that should be okay, but it's not the best suited sensor. It's used to measure both positive and negative current. That means large offset and lower resolution.
Hmm.. How big the error can be? I looked at these sensors because they are first cheap, and second - they have some kind of filtering and so on I guess.. I'm total noob in electronics.. Also I'm looking to shematics and I see some differences in them.. I will make the final one which I will try to make on breadboard, could you check it so I don't buy wrong components?

Well I can use ACS758 but then I have to make some king of pcb board and add some components to filter signal, if I remember correct that somewhere in this tread was mentioned that there are some problems with mesurements.. And I don't know what components to use.
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Old Sep 24, 2012, 12:42 PM
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The Arduino analog in can only read 1024 finite steps in the 0-5V signal. If you use a sensor that measures positive and negative current, you are immediately cutting the resolution in half, since half of the 1024 steps will be for negative current that you will never use. You also will need to offset the signal, since usually 0 current will be Vcc/2 (probably 2.5V).
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Old Sep 24, 2012, 01:02 PM
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Ace4 Thanks.. Now I understand little bit more about it..

Well up for suggestions I made these schematics where I put aside 2 popular shematics used in this tread with LM1881 chip..

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Old Sep 24, 2012, 01:05 PM
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Denmark, Capital Region of Denmark, Naerum
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Ace4 explained the resolution and offset pretty well

If you just want something that works, I would buy something like this:
http://www.flytron.com/sensors/60-ul...nt-sensor.html

But pretty much all current-sensors should work.
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Old Sep 24, 2012, 01:12 PM
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Denmark, Capital Region of Denmark, Naerum
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I'll try to answer the questions in your drawing.

The resistor and diode connected to D11 is used to output pixels (white). It doesn't matter if diode or resistor is placed "first".

Your drawing on "voltage divider" is correct with bat input - and yes, it's used to measure battery voltage. The different resistor-values in the voltage-divider depends on how much you want to divide the current, and how large a current you will allow. Doesn't really matter, but something like 10K resistors is a good place to start.

The current-sensor can be connected to A1, A2, A3 etc. you just have to set the pin in the config-file. I can't remember the default pin.

By the way, I can recommend to use the filter suggested in the LM1881 datasheet (little lowpass-filter). I tested it with good results.
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Old Sep 24, 2012, 01:52 PM
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Henry.'s Avatar
Sweden
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Just want to add that the 1N4001 diode MUST be replaced with a 1N4148 or similar fast one since the first one is to slow for the fast signals where the second is perfectly suited for this.

----

If a bi-directional sensor i used so would this only output half the voltage 2.5V when the Arduino could use 5V. The Arduino has, as said before, a resolution of 1024 steps at full 5V input which mean, that if you used say a 50A bi-directional sensor which only put out 2.5V out at max, that the smallest resolution that then could be measured would be 0.0975A (50/512). If not used a bi-directional then the full 1024 resolution could be used and thus 0.048A in resolution for the same 50A sensor.

I ordered the wrong bi-directional one but 50A so i should then get a resolution of 0.1A and that work perfect for me.

With a 100A sensor all the resolutions are double in value and with a 200A 4 times in value.
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Old Sep 24, 2012, 02:06 PM
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Latvia, Riga
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Henry thanks for detailed description.. Now I understand it even more..

I looked at LM1881 datasheet and this was what I could get out of it (look at picture).. Hope that I didn't add too much components.. I think those two additional capacitors are good but don't know about resistor R6 in video line.. Comments wellcome..

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Last edited by walkmanz; Sep 24, 2012 at 02:54 PM.
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Old Sep 24, 2012, 02:14 PM
HOL
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Quote:
Originally Posted by walkmanz View Post
Hi to every one..
Can I use this current sensor?

http://www.ebay.co.uk/itm/ACS712-Mod...item4abc72ca3a

Thanks..
According to the data supplied on the page, this sensor can output +/- 2 volts (66 mV/A = 0,066 * 30). So Your resolution will be (1024/5*2) 409 steps for 30 Amps, yelding 0,073 Amp/step.
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Old Sep 24, 2012, 02:42 PM
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Henry.'s Avatar
Sweden
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walkmanz I dont think that R6 and C3 in your schematic is used by anyone here, me included, but they get good clear picture anyway so i guess they could be omitted its more to filter the input but i dont think there would be any problems with that since it not that noisy that its needed.

The LM1881 works both for NTCS and PAL so its nothing to worry about.
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Last edited by Henry.; Sep 24, 2012 at 02:49 PM.
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Old Sep 24, 2012, 02:50 PM
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Latvia, Riga
Joined Jan 2012
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You are right but as Dennis mentioned that with some kind of low pass filter he got really good results, as these components are really cheap then why not to put them in..
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Last edited by walkmanz; Sep 24, 2012 at 02:54 PM. Reason: my mistake
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