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Thread: Super Simple OSD Mods (4s + RSSI)

  1. #1
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    Super Simple OSD Mods (4s + RSSI)

    If you're not familiar, HobbyKing carries a really cheap OSD that displays Voltage x 2 and time.

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    Even though HK rates it from 7.2v to 12v, I've tested it from 4v to 17.3v, which means it will work with a 4 cell. Past 17.3v, the text starts bouncing up and down and the reported voltage drops. But since the peak voltage of a 4 cell is 500mv lower, its not a big deal.

    In case you fry your OSD in flight, the Video In and Video Out pins are connected, so you'll still get video, just no text. This also means that wiring your plane initially is easier, since you only have to connect video to one pin, not two.

    Onto RSSI mods...

    EDIT: I just tested this mod with my DragonLink. Works great.

    The BAT2 port (not isolated) on the OSD has a voltage range from 0.3v to 17v. Internally, there is a voltage divider (with values 4.7k and 1k) that steps this down so the 3.3v micro can read it. This is nice if you want the voltage of a second battery, but the the Corona receiver has an RSSI range from around 0.7v to 1.4v. This means that you only get two steps of resolution over your entire RSSI range.

    Look what that Sparkfun tutorial did to us. Now the whole world uses Eagle

    By removing the 1k resistor, and therefore disabling the voltage divider, the range decreases from 0-17v to 0-3v, with the tradeoff of much greater accuracy. This fits the Corona RSSI voltage range better. However the OSD will still inflate the voltages, so 1v of input will read a lot higher (~6v) on the OSD

    On the PCB, the resistor you need to remove is in red. I recommend desoldering it by putting a solder blob on one of the pins, and then heating the solder blob until both sides melt, then just pushing it off
    Click image for larger version. 

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    I found that I didn't need any sort of buffer to condition the signal for the OSD. The RSSI voltage ripple was lower than what the OSD could measure, and the input impedance of the OSD was high enough that it didn't affect the receivers internal RSSI handling at all. The OSD read around 5v with the TX off and 9v with the TX right next to the RX antenna.


    And that is how you put your hard earned $9 to good use.
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    Last edited by Hmfpa; 4th March 2012 at 02:57 PM.

  2. #2
    Crashing Vitamin J's Avatar
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    Thanks for the write-up! It's cool that I don't have to make a buffer for the RSSI off my Corona and sweet idea to increase the resolution.

  3. #3
    I Like Waffles... SENTRY's Avatar
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    You guys never cease to amaze me.
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  4. #4
    I like boobs OO Thumb's Avatar
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    Quote Originally Posted by SENTRY View Post
    You guys never cease to amaze me.
    I second that comment. Having committed myself to simple set ups, you have covered everything I need with this mod, improving a great little osd.

    Thanks mate for a fantastic contribution.
    Failure is an option.................... I opt for it quite regulary

  5. #5
    WormBurnin' aaron_gx's Avatar
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    My OSD's are the HK version. I see this OSD has 4 pairs of pins. Mine only have 3 pairs of pins. Batt1, Batt2, Video. What is the fourth set of pins on the supersimple OSD?
    Get me a Crocodile sandwich. And make it snappy.

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    On the OSD, the four sets of pins are (Video In, GND) (Video Out, GND) (BAT1, GND) (BAT2, GND)

    Since Video Out and Video In are connected, you only need one

  7. #7
    Crashing Vitamin J's Avatar
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    I just finished doing the RSSI mods to my Corona and getting it set up with my E-OSD. I read 1v to 1.6v straight off the Corona, after doing the resolution mod the OSD read 5.56v to 9.11v, that's tons of resolution! Thanks again, this mod turns the cheap little OSD into an excellent tool.

  8. #8
    WormBurnin' aaron_gx's Avatar
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    vitamin J, it would be cool if you can post a vid in flight of your RSSI OSD. I want to see how badly your voltage fluxuates without buffer, and with the extra resolution. Mine is not bad, but its not smooth either.
    Last edited by aaron_gx; 6th January 2012 at 12:03 PM.
    Get me a Crocodile sandwich. And make it snappy.

  9. #9
    Crashing Vitamin J's Avatar
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    No sweat! I should get some good testing in this weekend. Rerouted the antenna on my Specter so now it's in a straight line and passes out the back through the tail boom.

  10. #10
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    Will this work with a DL reciever? Interesting. I have the same exact OSD. Not sure if there is something wrong with it or not though. On that specific OSD what is does a blinking red light mean when everything is powered on?

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