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WICED Smart Bluetooth

ShawnA_01
Employee

[On 5/30/2014, this entry was modified to enhance clarity]


In SDK 1.x.x, the function bleprox_mod_Create() makes calls to blecm_setTxPowerInConnection() and blecm_setTxPowerInADV().


Although SDK 2.x.x does not use bleprox_mod_Create(), we do see calls to the power control functions mentioned in thread title.

Within bleprox_mod_Create(), we see the following comments:


//default is 4dB

// 3 , -1, -5, -9, -13, -17, -21, -25 db

Question: What are the acceptable values to pass and how much granularity is there when controlling the transmitter on the radio?

1 Solution
ShawnA_01
Employee

Answer:

Per the technical reference manual, the radio will not transmit at greater than +4.0dBm.  


The silicon has nuances -- time, temp, process variation -- which can sway the transmitter.  Since it can never transmit hotter than +4.0dBm, there is a "rounding process" in steps of 4dB.


Think of the transmitter capabilities as entries in an array in C-Code:


signed int Power_Table[] = { 3, -1, -5, -9, -13, -17, -21, -25 };


Function calls to blecm_setTxPowerInConnection() round to the nearest value in the table and the middle value rounds "up".


blecm_setTxPowerInConnection( 4 ) = Maximum radio transmission, not to exceed +4dBm.

blecm_setTxPowerInConnection( 3 ) = Maximum radio transmission, not to exceed +4dBm.

blecm_setTxPowerInConnection( 2 )  = Maximum radio transmission, not to exceed +4dBm.

blecm_setTxPowerInConnection( 1 )  = Maximum radio transmission, not to exceed +4dBm.


blecm_setTxPowerInConnection( 0 )  =  -1dBm plus or minus variance of silicon.

blecm_setTxPowerInConnection( -1) = -1dBm plus or minus variance of silicon.

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Passing numbers higher than 4 is permitted but ignored and equivalent to using the value of 4.

View solution in original post

5 Replies
ShawnA_01
Employee

Answer:

Per the technical reference manual, the radio will not transmit at greater than +4.0dBm.  


The silicon has nuances -- time, temp, process variation -- which can sway the transmitter.  Since it can never transmit hotter than +4.0dBm, there is a "rounding process" in steps of 4dB.


Think of the transmitter capabilities as entries in an array in C-Code:


signed int Power_Table[] = { 3, -1, -5, -9, -13, -17, -21, -25 };


Function calls to blecm_setTxPowerInConnection() round to the nearest value in the table and the middle value rounds "up".


blecm_setTxPowerInConnection( 4 ) = Maximum radio transmission, not to exceed +4dBm.

blecm_setTxPowerInConnection( 3 ) = Maximum radio transmission, not to exceed +4dBm.

blecm_setTxPowerInConnection( 2 )  = Maximum radio transmission, not to exceed +4dBm.

blecm_setTxPowerInConnection( 1 )  = Maximum radio transmission, not to exceed +4dBm.


blecm_setTxPowerInConnection( 0 )  =  -1dBm plus or minus variance of silicon.

blecm_setTxPowerInConnection( -1) = -1dBm plus or minus variance of silicon.

.

.

.

Passing numbers higher than 4 is permitted but ignored and equivalent to using the value of 4.

View solution in original post

Anonymous
Not applicable

What is the default power output setting without making this call? Is it 0 dB or +4 dB?

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ShawnA_01
Employee

The default is +4dBm.


The spec calls for a 2.5dB loss via the on-board antenna, so you'll measure a bit less at the output.

Anonymous
Not applicable

Shouldnt changing the txPower levels affect the amount of current the chip draws?

I am cycling through all the dB settings above at the end of the create functon and dont see much of a difference at all in how much current the BT chip is drawin .. is this not the place to try these?

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ShawnA_01
Employee

One would think the current draw would indeed tightly track the transmit power level.  However the radio is only on for a very short period of time and without a power meter to measure the consumption at very fast intervals, you probably won't even see the increase when using a traditional ammeter. 

What equipment are you using to measure the power draw?

Are you sure the new transmit settings are taking effect?

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