Latest ELM327 Bluetooth module

[enslinm123]

Hey there Freddy,

First of all, hats off to you on a great project !

So I have been reading up on your project and got myself a cheap Chinese ELM327 pictured as a dual board dongle, but turns out mine has a single board (identified by ELM327 Identifier as a V1.5) with an unmarked Bluetooth chip similar to yours but with a FKCYM438 chip (which is basically the ELM chip) that they reckon is similar to the 25K80. Below is a picture of the circuit for reference.

Anyways, I wanted to find out how you determined which lines from the Bluetooth chip was TX and RX for the ELM chip ?

I have already opened up the 4 traces running towards the ELM chip, soldered some thin copper wire to the traces and tried to determine which is TX and which is RX to the FKCYM438 chip, I've tried almost all combinations without any communication success at all and am starting to wonder if I should not cut the traces eliminating the BT chip completely and retry again.

I did however determine that the middle two traces go to the FKCYM438's pins 6 and 7 (starting from the top right on the picture where the indent is as pin 1) if that could help.

So with all that jibber jabber out of the way, I just wanted to know how you determined which trace is which as that will help me a lot to move further with my Chinese ELM.

Thank you

PS: Photo is a bit blurry but it gives the general idea

[enslinm123]

Here is a more recent picture, showing the traces that I opened up.

Starting from the left (shortest soldered piece) goes to pin 8, next one over to pin 7, next one over to pin 6 and the last one to pin 11 on the FKCYM438 (the ELM chip).

So far I have not been able to successfully communicate with the FKCYM438 on either of those traces towards the FKCYM438 and tried all possible combinations. I do however suspect that the BT chip on this device is similar to yours so the pinout should roughly translate over to be the same.

I would really appreciate any inputs you might have on how I can go abouts finding the TX and RX traces to be able to communicate with the ELM chip.

Please note that I do not have an oscilloscope on hand to test with and I do not want to go the HC05 bluetooth route.

Thank you in advance.

[freddy-]

Hi enslinm123.

Anyways, I wanted to find out how you determined which lines from the Bluetooth chip was TX and RX for the ELM chip ?

I have used one of these cheap logic analyzers from aliexpress with PulseView software, I strongly reccommend you to buy one of these, they are really handy in these cases.

Looking at your pictures, I would say that it is probably SPI(miso, mosi, sck, cs), but only a logic analyzer will confirm that for us.

[enslinm123]

Hi Freddy,

Thanks for getting back to me.

Oh yes, I did not even think about a logic analyzer.

Thanks for the links, I've ordered myself one and it should be here in a couple of weeks to a few months depending on our customs.

Once I have it in hand I'll post again.