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Mr.RC-Cam

HeadPlay HD Goggle Upgrade: Add 5.8GHz Diversity & DVR

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Really nice tutorial, thank you so much!

I was busy designing a circuit around a MAX4090 myself for the same purpose (I noticed ImmersionRC used those IC's in the Uno receiver) when I stumbled upon your project around the  THS7314. Really nice work and thanks for sharing! Much easier with the THS7314 and less components! I ordered the parts and will start building the circuit soon. 

One question:
Could you explain me why R7 is 100 Ohm (and the same for R6 with Pot1 in serie)? I thought it would be 75 Ohm. Is it 100 Ohm because the impedance of the DVR-VID-OUT is only about 50 Ohm (and R7 and the resistor on the DVR-VID-OUT are in paralell so it creates +/- 75 Ohm)?

Thanks!!
 

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Could you explain me why R7 is 100 Ohm (and the same for R6 with Pot1 in serie)? I thought it would be 75 Ohm.

The 100 ohm buffer input termination value was chosen to increase the attenuated video signal to the correct amplitude. Then the buffer IC's output provides a 75 ohm compatible drive characteristic.

If your buffer is being used in a common video application (not specifically for this HeadPlay project) then you would normally use 75 ohms in those locations.

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I see, thanks for the explanation! 

And the only way to find out those R values was by using a o-scope and see what value gives an amplitude of +/- 1Vpp? 

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And the only way to find out those R values was by using a o-scope and see what value gives an amplitude of +/- 1Vpp? 

Yes, that's how I do it. For serious video work it's important to have a scope with TV-sync capabilities.  I also rely on a calibrated test pattern generator during testing to provide the precise 1Vpp video signal.

However, the recently published DiY FPV Video Test Cal Tool would be useful solution for FPV'ers on a limited hobby budget. It provides a low cost way of accurately checking an FPV system's video levels.
https://www.rc-cam.com/forum/index.php?/topic/4126-diy-fpv-video-calibration-tool-low-cost/

 

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Wow! Your FPV Video Calibration Tool is simply awesome and so clever! Thanks for sharing! I have enough Minimosd's laying around and will built it! I was already checking for a cheap o-scope with tv sync options, but found it to be too expensive for the few times I will use it (I mainly design/use digital circuits and use a Saleae Logic to analyze it). 

 

 

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Great! I think you'll enjoy building & using the Vid Cal Tool.

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I don't know if anyone would be interested but I have had 10 circuit boards made of MR RC cams  buffer circuit  for the headplays. Three of the boards are spoken for leaving seven that I would sell for $4 + shipping. I can provide a BOM (parts list) with Mouser p/n's  so that there is no need to look up part numbers, this also insures that the proper physical size of parts. I have not tested the board yet because I'm still waiting on my diversity receiver from Banggood  which is due in next week so I would like to wait until it is tested before I ship any out. The board measures 2"X2"

Thanks,

Mark

IMG_0228.JPG

Edited by luckyflyer

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Does it fit inside the 3D printed case I published? If not, how does it mount on the HeadPlays? Pictures would be great.

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I've had a difficult time finding someone that would print your case for a reasonable price. I may resort to having a Chinese company print me a few. Can you measure your case and give me the size of the area where the buffer goes in the case? After I submitted the artwork I did an exploded view of your circuit board and realized that your board appears to be about 1.6X1.6 inch, I should have done this before I submitted the artwork I know. These boards are cheap to have made though, I can easily get the size down to 1.6X1.6

 

Edited by luckyflyer

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If you look at the photo of my blank Perfboard you can determine the size.

parts1_1000.jpg

Each drilled hole is 0.1". So I estimate the irregularly shaped board is approx 1.4 x 1.5 inches.

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Thanks for doing it. Maybe you'll find someone to trade a PCB for a printed case.

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I would be glad to trade a board for a printed case. I have PLA in red, orange, green & yellow. If you don't want to trade, I am definitely interested in just the board. Have you taken a picture of this attached to the whole project?

Edited by hippyengineer

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