Voice Transmit on ble

[HakJae]

Hi. I am trying to transmit a microphone signal to the nrf52832 DK board.

Before development, i checked it by connecting a microphone(ADC) and a speaker(PWM) to one board.

This worked relatively well.

So i developed using two boards. One board(peripheral) is connected to a Mic and one board(central) is connected to a speaker.

After pairing, mic board transmit microphone signal to speaker board(128Byte). But the transmission speed is slow.

I refer to thingy F/W. Thingy Board's transmission speed is 6ms or 24ms. and my mic board's transmission speed is 30ms.

I tried to send it faster. but error has occured. err code is  'NRF_ERROR_RESOURCES'

Please help me solve this problem.

Thank you.

[haakonsh]

Hey HakJae,

From sd_ble_gatts_hvx API docs: 

NRF_ERROR_RESOURCES; Too many notifications queued. Wait for a BLE_GATTS_EVT_HVN_TX_COMPLETE event and retry. 

 

After pairing, mic board transmit microphone signal to speaker board(128Byte). But the transmission speed is slow.

I refer to thingy F/W. Thingy Board's transmission speed is 6ms or 24ms. and my mic board's transmission speed is 30ms.

Do you mean latency? If so what are your connection parameters?

 

Cheers,

Håkon.

[HakJae]

I used my cell phone to pairing on the thingy board. And i receive microphone data. In nRF Connect's log, the receive interval was repeated 6ms and 24ms. But my mic board's receive interval was 30ms. My mic board used Nordic UART Service.

[haakonsh]

"After pairing, mic board transmit microphone signal to speaker board(128Byte). But the transmission speed is slow.

I refer to thingy F/W. Thingy Board's transmission speed is 6ms or 24ms. and my mic board's transmission speed is 30ms."

Do you mean latency? If so what are your connection parameters?

[HakJae]

this is mic board, speaker board's connection parameters.

The connection parameters of 'mic board' and 'speaker board' are the same.

static ble_gap_conn_params_t const m_connection_param =
{
(uint16_t)MIN_CONNECTION_INTERVAL, // MIN_CONNECTION_INTERVAL MSEC_TO_UNITS(7.5, UNIT_1_25_MS)
(uint16_t)MAX_CONNECTION_INTERVAL, // MAX_CONNECTION_INTERVAL MSEC_TO_UNITS(30, UNIT_1_25_MS)
(uint16_t)SLAVE_LATENCY, // 0
(uint16_t)SUPERVISION_TIMEOUT // MSEC_TO_UNITS(3200, UNIT_10_MS)
};

[haakonsh]

What about MTU size and Data Length Extension? 

[HakJae]

I set the MTU size to 247.

#define NRF_SDH_BLE_GATT_MAX_MTU_SIZE 247;

nrf_ble_gatt_data_length_set(&m_gatt, BLE_CONN_HANDLE_INVALID, NRF_SDH_BLE_GATT_MAX_MTU_SIZE + L2CAP_HDR_LEN);

[haakonsh]

Hey HakJae, 
I still do not understand what your problem is. I need you to describe your symptoms in more detail, specifically what you mean by transmission speed and receive interval.

Cheers,

Håkon.

[HakJae]

I am sorry about my expressiveness.

I try to transmit microphone data.

So i should transmit 8000 bytes per second.

i setted the MTU size, and connection parameter as above. and i send 128 bytes each time.

Then i should be able to send more than 8000 bytes in 1 second.

but when i checked transmit speed, i could only send 4224 bytes in 1 second..

i want to improve the transmission speed.

please help me. thank you.

[haakonsh]

1. What is your connection interval?
2. Have you enabled Data Length Extension?
3. Are you testing throughput with our DK or a custom board?