Car MP3 player

In local supermarket I bought small car MP3 player. It cost about $25 (79Ltl). It is USB MP3 player with FM modulator. Just plug it to cigarette igniter socket, tune car radio, put your USB flash memory stick and enjoy the music.

mp3 player FM

I didn’t hope to receive good quality sound from such cheap device, but the real situation is much worse. The sound is full of interferences. Especially when there is some pause in your music. The interference is dual- from the car itself and from USB player.

Both interferences are solved in different ways. So, first of all, we must disassemble the device. It is very easy, just unscrew the fuse holder and remove the ring.

mp3 player FM

Inside you can see three PCBs: indication and control, FM transmitter, MP3 player and PSU. The red wire is just antenna and it tends to tear off. It goes from transmitter to car’s +12V line. So the car’s electric lines acts like big antenna.

mp3 player FM

That yellow capacitor is added by myself. This is the part of the struggle against interferences from MP3 player’s CPU and USB line. I also added one 470uF capacitor to USB connector. This decreased “reading from USB” noise.

The PSU of the player is very simple. (Component name come from silkscreen.) +12V from the automobile, L1 choke (too small to be significant), 22uF 16V (c17) capacitor, U5- UTC78D05L linear regulator, small ceramic cap and 100uF 6V tantalum capacitor. Now there are two linear regulators U2 for U4 for 3.3V and CPU BU9432-C1 Vcore. The CPU is made by Rohms. The comapny is very ugly- they didn’t publish datasheet of their products.

There is possibility to find player with switched regulator- there PCB traces for some small Switching Regulator instead of U5 and landing places for U1, D1 and L?. The Switching Regulator is much more economic device but more noisy. The power drain is quite big, as I replaced the fuse with appropriate inductor and it melted.

mp3 player FM

I found only this information about MCU and I only discovered that there are more features of the MCU than it is used.

The BU9432-C1 and BU9434-C2 audio system processor ICs implement a USB 2.0 full-speed host controller, an MP3 decoder, a D/A converter, and a system controller—allowing playback of MP3 files contained on flash memory via USB. The BU9432-C1 features a headphone amplifier, while the BU9434-C2 incorporates an SD card interface controller, a sound effecter, and I2S/SPDIF interface support.

The chips’ MPEG audio 1, 2, 2.5 decoder features a sampling rate of 8 to 48 kHz and a bit rate of 8 to 448 kbits/s, VBR. The D/A converter has 0.03% distortion, a 93-dB SNR, and an 88-dB dynamic range. The ICs have a FAT file system and are offered in TQFP64V and VQFP64 packages. ($5 ea/1,000—8 to 10 weeks ARO.)

The FM transmitter and stereo encoder is made on HY1417LP chip. I didn’t find any useful information in the internet about it.

mp3 player FM

Also, there is small serial RAM using 24C02 chip. It must store some setting in it, but I didn’t find it working, as after power-off the player starts playing from the beginning of the playlist.

On display and control board other chip, AM81SA10705, is placed. It is some sort like LED buffer and serial-parallel converter.

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33 Responses to Car MP3 player

  1. James Thompson says:

    I ordered a naked version of one of these from
    Unfortunately the seller didn’t have any information on the chip either. I emailed Rohm and they sent me an email back saying the person who handles questions was on vacation and couldn’t get back to me right away, but they did send me a catalog of their various chips. The catalogs didn’t have any useful information in them either, not even prices. They were very useful as packing material for items I needed to ship. I contacted them over 3 months ago and they haven’t gotten back with me. That’s one hell of a vacation. I plan to contact them again and see if I can get some sort of fire lit under their asses. If I get anything (useful) from them I’ll forward it to you. I would like to know if you can help me a little with the one I have. As I typed earlier the one I have was naked. It had no case and the simple instructions that came with it simply gave the buttons commands. I would like to know if you could send me via email a copy of the instruction manual that came with yours or at least let me know what mode the LEDs are supposed to represent (repeat, random, etc). Thanks.

  2. James Thompson says:

    I was emailed a PDF for the BU-9431-D1. Not an exact match, but close enough. Send me an email and I’ll forward it to you.

  3. rahimkv says:

    if you have the datasheet of bu9432-c1 or bu9431 and hy 1417lp, kindly e-mail me.

    thanks in advanced

    rahimkv india.

  4. hamid says:

    I also buy MP3 player like you ( same as photo ) .I would like to chang frequency in all FMM band ( 87 to 108 ) .I work with many synthesizer frequency IC but I didnt find any info about HY1417LP . Do you
    know how data for chose frequency send to HY1417LP? with which pin ?
    best regrds

  5. Read Lithuanian version comments. There is some datasheet information:

  6. andy says: – look for circuit and data of hy1417lp. pozdrawiam andy

  7. anonymous says:

    the same IC is used in a thomson-brand radio/alarm/clock type cd340usb which I recently aquired for 15€

    I’d be interested in the datasheet, too.

    Although it seems that there is not much to discover. I got curious as it detects mp3s that have been deleted. maybe the fat is damaged!?

  8. anonymous says:

    The IC couldnt play mp3s off a 128mb usb-stick dos-formatted on an older macos x (10.3.8 ?).
    no problems with fat32 formatting on windows.

  9. petalo says:

    The FM tramsmitter is the BH1417 from Rohm…lot’s of info on the net…!

    The USB controller has 2 versions, C1 and C2, C1 is standard (no more options), C2 has an Eq, Sound enchanger, enz enz

    Have fun…!

  10. Logger says:

    Could e-mail me the datasheet of am81sa10705 if you have?


  11. James Thompson says:

    Sorry for not responding sooner. Very busy. A small line of text from the email sent to me said “Please note that the 1st generation of ROHM’s memory host + media decoder solution was to be released as BU9432; however, the part number that actually went to mass production was BU9431”. That means the 9432 is the same as the 9431. I don’t know what your emails addresses are, so I’ll post my email here. Send me an email with the subject line of “Rohm BU9431”. My email is “moc.liamtoh@timmaj”. It’s typed in backwards to fool spammers.

  12. James Thompson says:

    I’m an idiot.
    My backwards address is moc.liamtoh@999timmaj.

  13. Vovchik says:

    It is possible to make in the given device function of memory at switching-off ?Here that has found:

  14. ajib says:

    please help me, I want not use fm modulator circuit, I will use audio out from mp3 player to aux in another amplifier w/o fm modulator, in my circuits saw IC HY1418, can helpme give me solution about it, thanks before

  15. Instead of searching for HY1418, look for BH1417F… 🙂

  16. tri says:

    I also looking for HY1418 datasheet, this 16 pin, i think this’s different with BH1417F….anyone have HY1418’s datasheet? tks

  17. paparak says:

    And i need some info for HY1418.I want to make outputs on my mp3 transmitter but there is no any examples.

  18. oha says:

    You are a genus
    please help me, i have the same MP3 player and i want to use it away from my car (inside home)
    i ask you
    1- It is possiple to use it with only usb port to take the power from(or use a special wire)?
    2- How can i extend the signal of transmitter ?

    plz help me i need it so much

  19. 1. Yes. If it is not some apple i-crap stuff. Apple use info from data lines to prevent users use “uncertified” hardware- no money for Steve Jobs. You can get stabilized 5V upto 100mA officially (up to 500 … 1000mA depending on hardware) from USB port. To make USB “power” port from other source is very simple- just connect stabilised 5V PSU to USB power pins. It is posible to use even simple 7805 chip for this.
    2. Best way to extend sygnal from transmitter is to user normal antena- simplest and best antena for FM is quarter wave wire. Lenght of wave can be calculated- divide light speed from frequency. The result must be something about 75cm (~30 inch).

  20. oha says:

    thanx alot for your quick response i really appreciate that
    1- the USB is work property.thanx
    2- but i dont know or not sure how to make antenna(or buy the right one) and how to connect it with mp3 player in good way??

    plz if you have a explanation
    thanx again.

  21. Attal says:

    You are a genus
    please help me, i have the same MP3 player and i want to use it away from my car (inside home)
    i ask you
    1- It is possiple to use it with only usb port to take the power from(or use a special qire)?
    2- How can i extend the signal of transmitter ?

    plz help me i need it so much;

  22. It is very interesting… look at messages from “Attla” and “oha”… They are identical, but from different IP and emails.
    Text is a bit random, but logical. Is it strange coincidence or there is new AI software is born?

  23. OHA says:

    its really weird, who is Attal and why he is copying my first massage ???
    what ever
    thanx alot for your quick response i really appreciate that
    1- the USB is work property.thanx
    2- but i dont know or not sure how to make antenna(or buy the right one) and how to connect it with mp3 player in good way??

    plz if you have a explanation
    thanx again.

  24. The only difference in these messages was that second comment had link to some webshop. 🙂

    Antena- is a piece of wire (~70cm lenght). It must be connected to output stage of transmitter (or/and receiver). In this mp3 player, original antena is few centimeters of wire, little sping, fuse and car’s inner wiring. This tingy must be inserted in cigarette lighter. And this socket typically is near car’s radio. So everything is working.
    If we need bigger distance, new antena (that damn 70cm wire) must be straight in the air.

    There is small image about antenna is this post:

  25. Jmudko says:

    I’ve got FM transmiter with 16 pin HY1418 and it seem that it’s like the one that andy gave
    pins 6 and 8 are inputs
    I’m gonna take the signal from there and put it directly into my car radio. No more FM radiation 🙂 And the sound quality should be much better.

  26. cvrc says:

    I have a very similar device, and not too good FM reception on the car radio. Does it make sense to unwire the antenna from the ground connector of the transmitter and connect it directly to the radio antenna input?

  27. Antenna is not connected to ground. It is connected to +12V via capacitor. So your car’s inner wires act like antenna.

  28. cvrc says:

    You’re right, it’s connected to the ground through coil, I was wondering what is that doing in the PSU (it’s around TD34063AM).

    BTW this is with remote control, both USB and MMC ports, reads folders (it was written on the packaging that it doesn’t :).
    My plan is to wire the ANT pin of the FM transmitter part directly to the radio antenna in. I’m not sure if there are not going to be more problems because it won’t go through capacitor, what would you recommend, should I add one? Or this whole action is in vain?

  29. cvrc says:

    Now when I’m thinking about it, it would be nice to make also a 3 way switch that enables me to change between external car antenna and the mp3 for the radio, but also enables to connect the device directly to the external antenna, hopefully reaching to the nearby cars.

  30. Cvrc: from your photo I don’t see antena wire. So I can not comment. But, in real world there is enough power from mine player to broadcast music for about 100 meters. And I don’t need any antena’s modifications. Too powerfull signal to antenna can cause distortions in sound.
    FM frequency is from 80 to 110 MHz and at this frequency any capacitor is transparent for any signal. If you have bad receive quality and strenght, better check your device with handheld radio out of the car. Maybe you car radio is well shielded from internal electronics interference? It is possible to tap antenna cable and “add” your broadcast.

  31. guest says:

    is it possible to make a line output from this fm transmiter?best regards

  32. Yes, FM transmitter and mp3 player are different devices (chips). Read datasheet.

  33. CableGuy says:


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