Steps to reproduce the problem

1. Connect MinimOSD to the APM in parallel to the Xbee or any other modem, following the instructions of the tutorial. Remember to do not connect the APM RX pin while using a parallel modem;
2. Connect video input (camera) and output (video TX) to the MinimOSD;
3. Do not tie Analog and Digital VCC;
4. Power up all systems, prefer using two batteries, one for video + MinimOSD and another to APM + Servos + ESC + Motor. I'm using three separated batteries, one just for ESC + motor, but it's not necessary to reproduce this issue.
5. Put your RC transmitter in "range test mode". I'm using Dragon Link, so the procedure is to use that 50 Ohms knob on TX to limit irradiation.
6. Execute range test and take note from the results;
7. Now turn off video battery and redo range test.

Expected output? What do you see instead?

The range decrease dramatically when MinimOSD is on. To be sure that the result is not compromised by video interference, you can also do the following test. To bypass MinimOSD connecting video TX at camera directly and power it up. Redo range test and you probably will see the issue.

Version of the product are you using?

MinimOSD V1.1 with APM 1.0

Please correct me if I'm wrong, but the analog power line is regulated by a switching circuit, right?

If this assumption is true, the cause is found. This switching circuit may be generating a considerable amount of electromagnetic interference at 433 MHz, as GoPRO camera do in the same kind of UHF RC systems.

Some other theory?

I am having the same issue.

Setup is - TSLRS UHF link - Generic 12v camera - 1W 1.2GHz Lawmate video transmitter, 60 cm away from the rest of the electronics - APM 2.5 with MinimOSD 1.1 - Separate 3 cells LiPo battery for video, powering camera, video transmitter, MinimOSD and microphone - Analog and Digital VCC not bridged on MinimOSD

With recommended range test procedure (UHF emitter antenna removed) I get 20 meters+ range. When I power the video link the UHF range drops to 1.5 meters.

If I connect the camera directly to the video transmitter I get full range back.

Isn't the camera side of the MinimOSD electrically disjoined from the APM side?

I'll try later to: - add a ferrite between the APM and the MinimOSD, or between camera and MinimOSD, see if there is any noise propagated from either the video transmitter or the camera - power the MinimOSD from a separate 5V linear regulator supplied from the 12V video battery to test the possible issue with MinimOSD onboard switching power supply.

Any other recommendation?

While checking for the best place to connect an external 5v AVdd I found out that I have electrical continuity between AGND and DGND. I did not bridge those on the board, but I have zero electrical resistance between the ground solder pads. AVDD and DVDD are electrically disconnected.

Is this normal? That would defeat the purpose of separate power supplies, methink.

Ok, another input: I added 12 turns ferrites near video in and video out of the MinimOSD, and range went from 1.5m to approximately 6 meters. Not good enough, but much better.

I am assuming that I have a noisy camera or video emitter, and that the noise is crossing to the UHF receiver through the AGND-DGND bridge.

2 questions, then: - Is it normal that AGND and DGND are bridged on my v1.1 board, or do I have a faulty PCB? - If it is faulty, where should I look to repair it (unbridge AGND and DGND)? I'm in EMEA and sending the board back for repair would cost too much, I think.

I still do not know if AGND and DGND are supposed to be connected, but I assume this is a bad idea.

I added an optocoupler on the digital input side, powering the minimOSD digital side from the video battery. I still had range issue. I then cut the +12v input to the analog side and bridged AVDD to DVDD and AGND to DGND (voluntarily, this time).

I now have full range back (20 meters), exactly the same as when the camera is directly connected to the video transmitter.

My conclusion is that the noise radiated from the analog side switching power supply is interfering with the UHF receiver.

Anyway, I now have great range AND a great OSD, so I am happy.

As I suspected! The step down regulator is messing everything.

Yves Riguet, could you please provide a wire skematic of your solution for everybody?

Hi Marcos,

I attached the wiring diagram that allows me to power the minimOSD and still isolate it from the rest of the aircraft's electronics. I am using an optocoupler, a bidirectional one because that's what I had available - this is what I usually use for any data transmission to a power transmitter, for example to a UHF downlink (RFD900).

I am using a UHF-friendly SBEC (any good SBEC, really). You could use a linear BEC instead or make your own from a 7805 linear regulator.

Hi Ives, Thanks for the heads up on the optocoupler. Would you have used a unidirectional one if it was handy? Which one. Have you used this isolation method in other areas of the aircraft? Thanks. Vik

any update on this? has anyone successfully been able to use minimOSD with a UHF system?

Very interesting the opto-coupled input solution. However, the noises on the OSD would rely on the quality of the filtering on the external uBec. The interesting part is that even using an ordinary uBec you still get the benefit of mounting it away from the other parts, with the plus of a ferrite ring as LP filter on the dc wire.

I'm changing this thread to "Enhancement" type.

Yves, Thank you so much for the workaround. Unfortunately I am not as technically inclined as you, and would really appreciate some clarifications, or even some photos of how you have isolated the minimosd. I am having horrible interference with my UHF system, crippling my range and basically making it no better than using 2.4 for RC.

If possible, could you contact me via email? raphaelkrengiel@gmail.com. I will make it worth your time! Best, Raphael

I've found v1.1 produces a strong RF spike around 459MHZ when using both power rails or just the 5v supply. Isolated the issue to the board by only connecting a 5v power and using different power sources. No matter what power supply is used the interference is the same, would this be the on-board regulator? How can we reduced the noise or change the frequency?

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If you want to bypass the on-board regulator and get rid of the noise, here's another way of doing it on a v1.1 board: http://www.rcgroups.com/forums/showthread.php?t=2175802