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I am using HC-05 bluetooth module for sending large data(80-100KByte) from my phone to arduino-uno. I had found that this module has a flash chip of 8Mbit (SST39VF800A) but the datasheet of HC-05 has nothing about buffering of the data to be transmitted or data received. I need clarity about the buffering of data so that I can change the data rate from the phone for better communication.

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  • Mhh, interesting question. As bluetooth itself is packaged, I think the module needs to at least buffer a few packages. This answer states, that maximum package size could be around 1KB. But to be sure, one would to read the firmware code or ask the one, who wrote that. I'm not sure, if that firmware is opensource.
    – chrisl
    Mar 3, 2021 at 13:05

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I didn't find any help in any data-sheets I could find, either. So I'd suggest a simple experiment, sending increasingly large packets before the other side attempts to read anything, until some data goes missing. The packets don't even need to be very sophisticated if all you want to know is whether N_received == N_sent and for what maximum 'N'.

Update:

All bytes were received correctly if there is no delay but with increasing delay in reading from HC-05 data was not fully received and with delay greater than 800ms only 63Bytes were received.

If you're collecting data as it arrives, then you can't measure the buffering. When you wait until all data has been set before you try to read any, the number of bytes you receive is the buffer size. It sounds like a 63 byte buffer, probably only what the HC-05's hardware UART can buffer, without using any of its memory to increase that.

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  • I did the experiment by sending 100B and 1000B of data separately which took 4ms and 70ms respectively. All bytes were received correctly if there is no delay but with increasing delay in reading from HC-05 data was not fully received and with delay greater than 800ms only 63Bytes were received.
    – Gamma Ray
    Mar 5, 2021 at 20:16
  • I think the buffer is FIFO since the data received were FIRST 63 bytes.
    – Gamma Ray
    Mar 5, 2021 at 20:30

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