Upgrade 8 channel receiver to 32 channel

After I received my Nano QX FPV I just couldn’t wait for the receiver I’ve already ordered. I knew my current 8 channel receiver wasn’t compatible with the immersion RC VTX.

But just to be sure it couldn’t be changed easily I opened up the RC701 8 Channel diversity receiver/monitor.
The actual receiver chip is an RTC6715. After reading the datasheet I found out it does support other bands, but those don’t included the frequencies I needed. So no quick fix there.
But the receiver chip also has an SPI interface. So I started to search and found some others that already figured out the SPI protocol and created an Arduino sketch.
info Info

First thing I needed to do was to enable the SPI mode. For this to happen I had to remove the pulldown from pin 7.
IMG_1398
That’s some tiny traces. I had to use a magnifier to do that.

Then I had to put in an Arduino and disconnect the SPI pins from the dip switches and connect them to the arduino. Because the receiver is an 3V3 module I’ve used an 3V3 Arduino Pro.

IMG_1401

I started on the right receiver module. The pins from left to right are MOSI (aka data in) ChipSelect (aka SS) Clock (aka SCLK). These connect to the Arduino pins 11,10 and 13.

Because this SPI bus is write only, I’ve hooked up the receiver on the left to the same pins. (don’t forget to disconnect from the dip switches)

Now just find 5V somewhere on the board for power, connect ground and connect a button (I used pin 3). The header is placed so I can connect an FTDI through the hole used for the dip switches when the case is closed.

IMG_1402

The RSSI pin from the receiver is hooked up to A0. When I long-press the button it does a full scan and then tunes to the strongest signal.

Now I just need to learn how to fly FPV 🙂

RX5808_SPI_Frequenz_32CHArduino_autoscan_v1

7 thoughts on “Upgrade 8 channel receiver to 32 channel”

  1. Hi! I am new in arduino. Can you help me to do same thing?
    I am going to use separate rx5808 module with Arduino pro mini
    Your connection diagram rx5808 to pro mini:
    5808 – pro mini
    CH1 – 11
    CH2 – 10
    CH3 – 13
    RSSI – A0

    Button GND+3
    Correct?
    You connected RAW to arduino, I cant see GND Arduino connection?
    Is that right?

    1. I think you are correct with the pinouts. GND is not connected because there is a common ground. (Arduino and rc5808 share the power supply so also share ground)

    1. I have been wanting to do that but I don’t have a race band transmitter to test. But I’ll do it anyway. Should be finished somewhere this week.

      1. Sweet, cheers. I like the simplicity of 1 button to autoscan without the need for a GUI. Love your work.

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