This is quite an old school problem, because I need to connect the AGFRC MRFS01 FASST receiver to the ZEUS F722 Mini flight controller. This FASST receiver has an RSSI output on a separate pin as a PWM signal. Unfortunately, the receiver cannot set the RSSI signal as one of the 1-16 signals in the s.bus line, which would allow easy setup in Betaflight. So the question is, is it possible to bring to the input of this flight controller a PWM signal in which the RSSI value is coded? Or must an LP filter be used to obtain the RSSI voltage value?
Thanks for the help.
Momo

There is the RSSI pad. You can wire the RSSI output from receiver to the RSSI on FC. You need to toggle the RSSI ADC feature on the configuration tab in BFC.

Thank you for the quick response. I know about the RSSI pad on the FC, but I would expect that there must be a voltage value that will be converted by the ADC. The PWM signal is not a voltage value, but a modulated signal. Therefore, an LP filter is usually used to perform demodulation to a voltage value. So the advice is that I should connect it directly without an LP filter?

It was late last night when I replied. Missed the PWM part. So yes, you need a LP filter to convert the PWM to analog output. But there is possibility another way. I personally never try it, but hear me out. So according to the configuration file, you have three PWM inputs. They share resource pin with a few uarts (see below) . In theory, if you just wired to one of these pins, and set the rssi_channel according, you should get the RSSI into the FC. Well, only PWM1-3 are available. And if you use one of these channels, you will conflict with AERT which is ch1-4. But you can reassign whichever was on channel 1, 2 or 3 in your radio to a different channel, and tell BF your changes via the channel map settings. You can also instead just remap and assign one of the UART to eg PWM 8 and you will not have conflict. This is just a theory. Even the BF remap wiki has the "?" next to PWM input.

resource PWM 1 A02
resource PWM 2 A01
resource PWM 3 A00
resource SERIAL_TX 2 A02
resource SERIAL_TX 4 A00
resource SERIAL_RX 4 A01

That sounds interesting and that's what I originally meant, if there is a way ...
How can I remap and assign UART input to PWM more than 4?
I'll definitely try it, but FC is on its way to me right now, I hope it will be here soon.
Finally, I will compare the difference between the ADC and the PWM version of RSSI.
Thanks.

When you do a list your resource, you can you will see that there are 8 PWM. In your FC, there will be three PWM assigned. Let assign the resource on PWM 1 (A02) to PWM 8.

In CLI


In theory, if now you solder RSSI from receiver to UART TX2 pin. And select channel 8 for RSSI, you should get some RSSI value. Sometimes the RSSI is inverse.

set rssi_invert = ON

I did read something interesting. See the excerpt below. Might be worth trying.

https://github.com/betaflight/betaflight...s-receiver

OK, I understand that. The FC should have an unused UART TX3 pad, so I'll try to remap it to it.
As for the inversion, I have found it before, as well as the LQ of the s.bus signal based on the number of lost packets per time interval (set_rssi_src_frame_errors). I read somewhere that this is not a very good parameter for determining link quality, because a very short time interval is monitored, which does not actually correspond to the real status of the transmission channel, and it was added to betaflight for those who did not have RSSI signal from the receiver on Futaba receivers. It would probably be best to display both in the OSD at the same time, but I don't think that's possible.

so i was really curious as to whether my theory will work. i tried it and realized that it will not work. first off, to get PWM input to work, you have to select PWM receiver. If you selected serial based receiver, it disable PWM. just from that, you can't have serial and PWM working at the same time.

anyway, I went further to see if I can even input a PWM through a serial UART that shared the same resource. I set to PWM for receiver. and input a PWM signal to an UART TX. I got nothing.

sorry to break the bad news, but I think your only option is a LC filter.

Thanks for trying it, for sacrificing time. I will use an LP filter, it is not complicated for me. At least we tried it, if you don't try, you never know ...

Yesterday I finally found the time and solved the connection of the RSSI output from the FASST AGFRC MRFS01 receiver to the Zeus F722 Mini. First I looked at the output from the receiver on the oscilloscope, the output was PWM at a frequency of about 110 kHz (very unusual), the full signal corresponds to a pulse width of 95% and no signal 5%. Just for testing, I connected this signal directly to the FC on the RSSI pad, but of course it showed fluctuating meaningless value, I was not surprised. Due to the high frequency, an RC low-pass of 1 kOhm and 100 nF only is sufficient. After connecting the low-pass filter, Betaflight shows an RSSI value of about 5% without signal and 95% with full signal from Tx, so it displays absolutely exactly according to PWM. In the CLI, I set the necessary parameters rssi_scale and rssi_offset and now I have the RSSI values exactly as they should be in the range of 0 to 100%, so the problem is solved.

Great. Thanks for the good info.

Hello colleagues.
I have an AGFRC MRFS01 FASST receiver, Futaba 14sg, cinelog 35 - GEP-F722-45A AIO.
There is no RSSI pin on the FC board. Is it possible to output from AGFRC MRFS01 FASST RSSI to another pin on the motherboard?
Is it possible to reassign any contact?