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I've been trying to build an FM broadcast receiver for the last few weeks know, with simple designs like with LC circuits, but I've realized that an IC based radio outperforms simple transistor radios. I've started looking a round for cheap FM receiver chips, and I've found one that is used in many soldering kits, called the RDA5807FP. I found a schematic online for the soldering kit, as pictured below. radio

I also looked at the datasheet, and it seems like it wouldn't work in the above configuration. By default, the chip is muted, and it seems like there is no way to change that, besides with I2C. I2C is volatile (I believe), so if they programmed it once with I2C and turned it off, everything would reset, and the chip would be muted again, leaving us with the same problem as before. The only way the datasheet says that it can interface is this: "Only support 2-wire bus interface", so (I believe) it is referring to the earlier-mentioned I2C. Even the example circuit in the datasheet is configured to work with I2C:

more radios!

So, my question is, how does this simple FM receiver work without a microcontroller? Is there something in the datasheet that I'm missing?

I'm also open to suggestions about different chips, along as it's simple, cheap, and still produced.

Thanks for all your help, and I apologize for my beginners ignorance.

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  • \$\begingroup\$ You are not missing anything. This part is controlled by I2C. The volume is set to max at power up so maybe that's why it is in mute mode. \$\endgroup\$
    – Rodo
    Sep 21, 2023 at 2:38
  • \$\begingroup\$ @Rodo If it is controlled by I2C, then how does the circuit that is used in simple soldering kits operate? That circuit isn't using the I2C interface, and in fact, it has buttons on the SCLK and SDA pins. Thanks for your help, BTW. \$\endgroup\$ Sep 21, 2023 at 11:01
  • \$\begingroup\$ Seems a similar chip (FM 1310?) is self-contained, requiring no I2C - however, pinout appears different. Not to be confused with MC1310 stereo decoder chip. electrodragon.com/product/fm-radio-module-64-108mhz-wo-mcu \$\endgroup\$
    – glen_geek
    Sep 21, 2023 at 13:05
  • \$\begingroup\$ It is curious that RDA5807FP data sheet shows pin #6 GND, while OP's schematic shows pin #6 VDD. The purpose of this pin is not documented. IMO a somewhat sketchy data sheet. \$\endgroup\$
    – glen_geek
    Sep 21, 2023 at 13:50
  • \$\begingroup\$ @Charlie Nicholson: Can u provide a link to this "simple soldering kits"? \$\endgroup\$
    – Rodo
    Sep 21, 2023 at 17:27

2 Answers 2

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I think the RDA5870FP is a programmable FM Radio chip can be controlled in a simple way with push buttons when pin6 is held High. Then the GPIO pins 1,7,8,15,16 are then: power, ch-, ch+, vol-, vol+ and there is a datasheet, RDA7088, which refers to this configuration. When pin 6 is held lo, then it can be controlled by i2c with rds and i2s output, which is shown in the RDA5870FP datasheet.

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**Danger! This circuit with the RDA5807FP (**HEX3653); has SEVERAL PROBLEMS:

  1. THE CIRCUIT WITH THE NPN TRANSISTOR DESTROYS THE IC! THIS POWER ON OFF function MUST NOT BE USED IN THIS WAY!! BECAUSE THIS CONFIGURATION WILL DESTROY THE IC!! BECAUSE DURING POWER ON, THERE IS A VOLTAGE OF 0.88 V ON THE AUDIO PINS 12 AND 13, WHICH REVERSES THIS VOLTAGE AS A NEGATIVE VOLTAGE WHEN THE IC IS TURNED OFF BY THE TRANSISTOR! THE CMOS IC CAN’T TOLERATE THIS! THIS CIRCUIT MUST BE OMITTED!! THIS IS MANDATORY! FURTHERMORE, THE CIRCUIT AT THE ANTENNA INPUT HAS AN INPUT LEVEL MUCH TOO SMALL FOR THE IF!! THE RESULT IS A POOR RECEPTION!! THE LEVEL HERE IS JUST PRESET AT 0.3 dbm! THE LIMITER DIODES ARE MANDATORY! SO NOTHING LEFT FOR FM STATION RECEPTION!!! THIS MEANS THAT HERE THE IF IS PRACTICALLY SLOWED OUT TO THE EXTENT THAT RECEPTION IS REALLY NOT POSSIBLE! THERE IS NO REMEDY!! IT MAY HELPS AN UNREALLY LONG WIRE WITH AT LEAST 1 METER, BUT THIS IS NOT AN OPTION IF YOU WANT TO INSTALL THE RADIO KIT INTO A CASE OR RADIO! A telescopic antenna is practically WITHOUT sufficient reception power! Therefore: The RDA5807 FP (**HEX3653) is NOT REALLY USABLE!! CONCLUSION: THE POWER ON OFF FUNCTION, CONTROLLED VIA THE NPN TRANSISTOR FROM THE AUDIO OUT PIN IS POINTLESS!! BECAUSE THAT WILL DESTROY THIS IC!!! UNFORTUNATELY!! The resistors included in the kit MUST be used AFTER the decoupling electrolytic capacitors!!! THIS IS ALSO MANDATORY!!
  2. THE FM RECEPTION of these two ICs IS UNUSABLE WITHOUT AN APPROPRIATE ANTENNA LENGTH OF AT LEAST 1 METER!! ANOTHER NOTE ABOUT THE CIRCUIT REGARDING THE I²C BUS: THE CONTROL USED HERE WITH BUTTONS FOR TUNING ON THE SDIO AND SCLK IS FUNCTIONAL, BUT THERE IS NO INFORMATION ABOUT IT IN THE MANUFACTURER DATASHEED! I found this circuit interesting at first, but I quickly had to experience the aforementioned for myself! AND IF THE PIN 6 HERE HAS TO BE SWITCHED TO VDD INSTEAD OF GND, THAT CAN ONLY BE A SPECIALLY PROGRAMMED GPIO THAT SWITCHES THE I²C BUS ON OR OFF HERE!! BECAUSE, AS MENTIONED, THERE IS NO DOCUMENTATION IN THE DATA SHEEDS!! THE SAME THING DESCRIBED HERE ALSO APPLIES TO THE HEX3653 FM RADIO IC - IN THE DIY KIT WITH THIS IC WHICH IS PIN COMPATIBLE AND FUNCTIONAL SAME TO THE CIRCUIT VERSION HERE OF THE RDA5807FP (*HEX3653 ALSO!)!! AS PROOF: I HAVE SET UP THIS RADIO KIT 10X AND THE FINDINGS ABOVE LEAD TO IT DESTRUCTION!! I was at least able to “save” 3 kits after the kits that were first manufactured!!(SEE POWER ON/OFF FUNCTION) ON THE AUDIO PINS! So: STAY AWAY FROM THIS FAKE CIRCUIT!! IT DOES NOT WORK ERROR-FREE AND WILL DESTROY THESE ICs!!!
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    \$\begingroup\$ Please don't shout, change to regular caps. \$\endgroup\$
    – Voltage Spike
    Apr 3 at 16:05

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