Sign in to follow this  
Followers 0
Mr.RC-Cam

DiY FPV Video Calibration Tool. Low Cost!

6 posts in this topic

FPV Video Calibration Tool: DiY -- Low Cost -- EZ to use.

The calibration of our FPV system's vTx / vRx composite video signal level (amplitude) matters a LOT. Unfortunately many are incorrectly adjusted out of the box. There's a number of reasons for this -- marginal designs, poor manufacturing QA, compatibility problems due to brand mixing by end users, cheap component drift, and just plain bad luck.

Hold on you say! You are convinced that your system's video is fine. But perhaps that's wishful thinking. Here's the cold hard reality -- Many FPV systems have marginal video levels and this invites problems that are often blamed on other things. For example, the random "weak signal" blackouts we all hate are not always directly RF signal related. Poorly calibrated video levels will cause those random blackouts too. Plus a host of other image quality problems that are simply victims of marginal video levels.

Checking the composite video signal normally requires an oscope (oscilloscope). Ideally a test pattern generator is also used to provide the 1Vpp standard video signal that is measured with the oscope. Not many hobbyist have access to this equipment or know how to correctly perform the measurements.

So I experimented with video level testing using simpler tools than a oscope. My goal was to have something that worked well, but was cheap and simple to use. After a bit of head banging a clever DiY solution was born. How does ~$20 USD and a couple hours work sound to you? Yes, really.

Here's what my DiY FPV Calibration Tool looks like.

Full_Assy1_1000.jpg

 

Spoiler alert: Inside the small 3D printed plastic box is a $8 eBay circuit board and a 9V battery. To calibrate a FPV system you'll need two of them. Both boxes will use identical hardware but with different firmware. Oh you guessed it, Arduino is involved.

Come back soon. I'll show you how to build and use it. Your FPV system will thank you. The world will be a better place.

 

Share this post


Link to post
Share on other sites

Interesting :)

 

Terry

Share this post


Link to post
Share on other sites

The magic behind the Video Cal Tool relies on our eyes' ability to easily see relative differences in brightness during a side-by-side comparison. The basic test setup is as follows:

(1) A monochrome video overlay provides a video reference (comparison) target pattern on the FPV display (goggles or monitor). It is directly connected between the FPV vRx's Vid-Out jack and the display.
(2) A second video source provides a mating target pattern. It is directly connected to the video input of the FPV vTx (the FPV camera is removed).

During the test the vTx's pattern is superimposed on the vRx's reference pattern. The mating target sets will have matching brightness when the FPV system's video level is properly calibrated. To account for the display's dynamic range and/or gamma behavior, one target set has 80% luminance and the other has 120%.

Here is the vTx test pattern:

Vid_Cal_vTx2_600.jpg


Here is the VRx reference pattern:

Vid_Cal_vRx_600.jpg

 

Ok, so that's what the vTx source and reference vRx targets look like. But now you're asking, how do you use them to measure the video signal's level (amplitude)? Answer: Your eyes are the "measuring" equipment. When I say using the tool is EZ, I mean it!

During the test the T-target pattern fills the empty inside area on the R-target. Properly calibrated video level appears on your display monitor as shown below.

Vid_Cal_targets_600.jpg


But if the two interlocking patterns do not blend together (brightness not the same) then the FPV system's video level is incorrect. Here's two examples:

Vid_Cal_bad1_600.jpgVid_Cal_bad2_600.jpg


What do you do when the brightness does not match? Fortunately this problem can be fixed on most analog 900MHz / 1.3GHz /  2.4GHz FPV video systems since they usually have an adjustable video level POT (variable resistor) in the vTx or vRx. Unfortunately modern 5.8GHz systems don't provide a calibration POT, so if the test fails you will be out of luck. But at least you will know that your 5.8GHz system has a video level problem.

Share this post


Link to post
Share on other sites

So it's time to gather the parts to build this cool tool. As mentioned before, you need two video target pattern generators; One for the FPV vTx and another for the vRx. The target patterns are provided by low cost Arduino based FPV OSD boards.

Here's the Parts List:
2 pcs, MinimOSD (KV Team version recommended). Approx $8 USD each on eBay and AliExpress.
minimOSD_pcb2_600.jpg


To flash the custom firmware you'll need one (1) of these:
FTDI FT232RL USB to TTL Serial Converter (6-Pin version) for Arduino. Approx $3 on eBay and AliExpress.

FTDI_usb1_600.jpg

 

Keep in mind that there are several similar looking Chinese clones of the MinimOSD on the market. I recommend the "full size" board that has the KV Team Mod (built-in voltage attenuation resistors). Here is what the KV Team version looks like:

minimOSD_pcb1_800.jpg

How to tell the difference in board versions: The KV Team version will have the JP6 8-Pin header area (8 empty solder pads across the top). See photo above.

Useful Info:It's important that both OSD's have identical video signal characteristics. Therefore, I recommend that you purchase both boards at the same time from the same supplier. This should reduce the chance of any component variations that might cause unmatched video levels.

You can use your existing 7-12VDC FPV batteries (3S LiPO is fine) to power the boards. No other components need to be purchased. But if you want a power switch, A/V connectors (I used RCA phono chassis panel jacks), or plastic enclosure, then feel free to add these things to the shopping list.

Although you can simply protect your OSD board with some heatshrink or duct tape, the 3D printed plastic case gives it a professional appearance. Here's the STL files for it.
  Case Base: case_base1.stl
  Case Top: case_top1.stl
  Case Hole Plug: case_plug1.stl
Printing recommendations: ABS filament, 35% infill, 3 layer shell, 101% size scaling (shrinkage correction).

plastic_case1_1000.jpg

 

There's room for a mini toggle power switch, Alkaline 9V battery, and RCA panel jacks. The "Case Hole Plug" file is a small piece that covers an unused RCA mounting hole on the vTx pattern generator (Vid-In is not needed on the vTx side).

Here's how everything fits inside my vRx target generator:

Full_Assy2_1000.jpg

BTW, the vTx looks the same, but has only one RCA jack.

Share this post


Link to post
Share on other sites

Assembling the vTx and vRx video generators requires basic soldering skills. And in case I have not been clear, there are two (2) MinimOSD's used in this project.

First you need to connect some ground and power pads that are on the two MinimOSD boards. Just add a blob of solder across the pads shown below (Grounding pads on bottom side, SJ2 pads on component side). Some suppliers have already done this for you, but if the pads are not bridged then you must do it.

solder_blob_gnd_1_1000.jpgsolder_blob_SJ2_1_1000.jpg

 

The new firmware (to be flashed later) includes an optional battery voltage monitor feature. This requires adding a jumper wire, as shown below.

bat_jmpr1_1000.jpg

 

If your MinimOSDs are the old/original version (not "KV Team") then the voltage monitor feature will require adding some 1% 1/8W resistors, as shown below.

minimOSD_atten1_700.jpg

 

Each boards' Power and Video connections are available on the stacked 3-Pin headers. The pins are labeled on the bottom of the MinimOSD board. The vTx OSD only uses VOut and +12V power pins. The vRx OSD needs VOut, VIn, and +12V. I used 3-pin servo plugs to connect the MinimOSD boards, but direct soldering can be used instead.

wiring_bot1_1000.jpg

The video connectors you use are up to you. I installed RCA phono panel jacks and made some simple adapter cables that connect them to the FPV system. How you do this is your choice. As a reminder, the vTx's MinimOSD does NOT use the VID-IN signal, so be sure to omit it.

 

Share this post


Link to post
Share on other sites

Firmware flashing comes next. So come back soon for the details!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0