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helipirate

Futaba RSSI

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I have searched through most of the forums and I hope this is not somewhere else, if so please direct me to the correct topic.

I have a Futaba 14MZ with R5114 receiver (72Mhz). I am using the inspire OSD on my Trex600 and so far the whole project is going along nicely!

I want to use the RSSI on the OSD, but I cannot find anywhere that can help me find out the following:

1. Does the Futaba R5114 receiver have an RSSi pin?

2. If Yes, Where is it on the circuit board?

3. If anyone has any data about connecting the R5114 to the RSSI input on the Inspire OSD ? Maybe buffer circuits needed etc.

Great Forum, I have read so much here that has helped me along the long road to FPV success.

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One solution is to open up the Rx and locate the FM demod IC. Then find the data sheet to it and see if it has a RSSI pin. Some Rx's are constructed in such a way that it makes this task impossible, so be prepared for that.

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Thanks Mr RC-Cam.

I have opened it up, the problem is the chip (I am pretty sure its the right one) has Futaba code and no other manufacturer IDs.

Kinda makes it hard to check out the pint outs. Number is FP6350B. The only other number s 612201J. Anyone have any ideas about the possible pin outs? I thought of probing around with a DMM and seeing if I could see a voltage thats changes when the tx is turned off and on... I figure that if there is a rssi then it should drop to low value when there is no tx signal present. I am not sure how these work but there must be someway for the receiver to know when to switch to failsafe...I wonder if its using RSSi or some other method??

This receiver is actually the 5014, I use the 5114 and this is the obsolete and dodgey cousin that futaba stopped producing. I figure they probably did not make that many changes and I am playing with this one before I open up the new 5114.

The only other thing I see on the 2 boards that could be a chip (from its size and apart from a suspiciously op-amp looking 8 pin job). is housed inside a can. I figure its probably the oscillator though, because its on the piggy back board surrounded by crystals and RF tuning coils and what appears to be receiver front end circuitry. I am not opening the can to peek, I dont believe its a chip.

Any information or suggestions is appreciated!

I am going to start my probing so I will post the results (maybe kaboom!).

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Are you sure the FP6350B is the FM demod IC? My gut feeling that it is the microcontroller for PCM decoding.

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Are you sure the FP6350B is the FM demod IC? My gut feeling that it is the microcontroller for PCM decoding.

Absolutely, positively dont know! I am an old RF engineer from the days of discreet components where the high powered stuff still used valves! I have not played with radio gear for 28 years! My eyes are also not what they used to be. so I would trust your gut feeling over my observation anyday...

Anyway.. upon further squinting I can see a little chip on the "RF Board" sandwiched between the 2 boards. Maybe this is the thing I am looking for? Ye gods, unless I break out the micro desolderer, a large magnifying glass and the ACME hand steadier MKVI, there is no way I will be checking its pinouts for anything! Besides, I would have to rig 11 connectors to keep the boards functioning while apart.

I can see this is fast becoming an exercise in futility, unless Futaba would release a circuit diagram and board layout! Somehow I don't think they will be doing that anytime soon!

Below is a couple of pictures of what I am up against...I am open to the wildest suggestions - apart from buying another receiver!

Does your gut have any feelings about a good place to prod with the DMM?? Is there any reason the rssi would make the trip to the other board with the big (maybe PCM decoder)?

post-4369-1206981337_thumb.jpg

post-4369-1206981424_thumb.jpg

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The picture of the big "Futaba" chip is the PCM decoder (servo encoder) microcontroller. The FM circuitry is definitely somewhere else on your Rx. I doubt that they have a convenient RSSI test point for you to utilize, but anything is possible.

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Mr RC-Cam...

Well after some prodding about with the DMM I have these results..

The pin in the picture puts out 1.987 volts when the TX is turned on next to the receiver. When the TX is turned off it drops to .667 volts.

Then when I moved the TX into another room in my apartment with 1 brick wall in the way, the voltage dropped to 1.877 volts. When I moved the TX into the bathroom (3 brick walls away) it dropped to 1.574 Volts. I put in inside the bath (without water!) and the voltage dropped again to 1.398 volts. Bringing the TX back into the room next to the RX and the voltage read 1.987 again....

Do you think I may have it? Seems like a valid result to me, but with my lack of experience in these RX I am not sure. Are other RSSI voltages similar?

Next I am going to try the 5114. Oh and using a DMM did not seem to affect the signal (servo testing while TX is in other room).

If you agree then we could extract this picture and use it as a reference for everybody.

post-4369-1207020883_thumb.jpg

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Well Well, I have been smiled upon!

The pin is correct, it is the RSSI pin for both the Futaba 72 MHz G3 receivers 5014DPS and 5114 DPS. The voltages vary slightly between models but low (no signal) is .667 V and .775 respectively, and high (full strength signal) is 1.987v and 2.21v.

I soldered wires to the ground and RSSI pinout, plugged them into the RSSI input on the OSD and Bingo! it works like a charm. A walking test recording to my MP4 player from the video RX shows the signal strength indicator working like a charm.! When RC TX is turned off the OSD RSSI indicator flashes to note no signal and the indicator drops to 0, when TX is on and as I move towards the Heli the signal indicator moves upwards!

Mission Complete! I hope this helps anyone out there trying to do the same thing!

A final pic to show the pins I used.

post-4369-1207044231_thumb.jpg

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Thanks for posting the information. It should help others that are looking to utilize RSSI in their projects.

It is a rare treat to have such convenient access to the signal. I wish all the Rx's were like that!

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Well Well, I have been smiled upon!

The pin is correct, it is the RSSI pin for both the Futaba 72 MHz G3 receivers 5014DPS and 5114 DPS. The voltages vary slightly between models but low (no signal) is .667 V and .775 respectively, and high (full strength signal) is 1.987v and 2.21v.

I soldered wires to the ground and RSSI pinout, plugged them into the RSSI input on the OSD and Bingo! it works like a charm. A walking test recording to my MP4 player from the video RX shows the signal strength indicator working like a charm.! When RC TX is turned off the OSD RSSI indicator flashes to note no signal and the indicator drops to 0, when TX is on and as I move towards the Heli the signal indicator moves upwards!

Mission Complete! I hope this helps anyone out there trying to do the same thing!

A final pic to show the pins I used.

You wouldn't happen to know where the RSSI is on a Futaba R319DPS? I've done a lot of prodding and came across one pin that seems to be a likely culprit. It wasn't easy to find either. However this voltage when next to the transmitter (9C) is around 1.2 volts. Turning off the transmitter it drops to around 0.5 and continues to slowly discharge down to 0. The voltage does get lower and lower the farther distance you go and while flying, it seems to stabilize around 0.2 volts. Weird. Most RSSI's i've found have been leading back to an IC chip somewhere on the board and have been inversed (Low signal yields a high voltage and vice versa). The pin I found may be it but it doesn't fully fit the description. Just wondering if anyone has had some experience finding it.

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I have a feeling that the signal you found is conditioned RSSI that is being used for a basic AGC function. The ideal solution is to identify the FM demod IC and then follow the IC's data sheet for RSSI info. Or keep on probing. :)

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a nice little demo video with the osd would have been cool :-)

but ok I think you need to unmount your TX antenna,

and then walk/run the 100meters with plane and osd will look funny ?

I suggest you adjust the bars so you have a nice 0-100% bargraph

indication, make zero bars = rc fail, and one bar = jitter

and so on, then you know exactly how far to can go away

and still have a nice margin,

remember to put your address and phone number on your plane :-)

one of my friends just lost an FPV plane 5km away due to video range loss,

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