DFR0781 (B401) SD-card not reading
Per.Svensson 2025-04-23 22:59:06 439 Views4 Replies I have a BT401 module with firmware VER2.3-20191228
Playing music over bluetooth audio works perfect, but switching to SD-card using AT+CM03/r/n over the UART does not work. The command is accepted but returns ER=5 ( Device offline or abnormal)
I have searched the entire internet for help, but all I get is instructions to format my 8GB card to FAT32 and to clean the contact fingers etc. All this is of course already done, but with no success.
The electrical connection is like the picture below. "Card detect" is not used. I assume it is not necessary?
A schematic showing the standard connections would be helpful
I have also tried other brands of SD cards but none of them work.
Could it be that VER2.3 lack support for playing via SD-card?
I really have no ideas left now. Any input from the DfRobot team would be much appreciated.
/Per
Double-check all connections between the BT401 module and the SD card slot. Check if the SPI lines (MISO, MOSI, SCK, CS) are correctly connected.
Verify that the SD card is receiving the correct voltage (typically 3.3V).
ahsrab.rifat Thank you SO MUCH for this find Tonny! I never found this schematic during my internet scan.
Yes you are right. There is a difference in how they use the clock signal. It seem to have a double use.
Probably for determining whether a card is inserted or not.They probably change direction of the SDCLK at some point to check the CARD_INSERTED pin of the card holder.
This is NOT mentioned in the BT401 data sheet so I am very grateful that you found this schematic.
I will test to add this 3k resistor and report the result here. It should be important to other users as well.
/Per
Per.Svensson I have found the schematic diagram, which you can refer to. Additionally, I think the issue might be with the SD circuit; you may want to check that.
Tonny12138 Hello again Tonny
Your schematic certainly helped!
Adding the 3k resistor was all that was needed.
It is obviously used for Card insert detection.
Strange that not a dedicated input on the module was used for this.
Again, Thanks for your supportiveness!
/Per
