[Tinyos-help] Calculating RSSI in dBm locally on a mica2 mote

[Sean Casey]

Thanks for your quick reply.  I neglected the fact that the value was 
being stored in flash as an unsigned number.  Thanks for pointing this 
out for me.

- Sean



Michael Schippling wrote:

> 200 (decimal) is a negative number in an 8 bit signed int...about -55.
> Does that make more sense for your level?
> MS
>
> Sean Casey wrote:
>
>> Hello,
>>
>> I'm working with mica2 motes and I would like to know if it's 
>> possible to calculate the rssi value in dBm on the mote locally.  I 
>> had been sending the rssi value to the UART and then calculating the 
>> dBm value with a java program, but now I would like to calculate it 
>> locally on the mote, and store it in flash.  I've attempted this and 
>> I'm not getting a value in the right range. This is what I've been 
>> using:
>>
>> /* Calculate the RSSI Value */
>> V_RSSI = 3.0 * (RSSI_VAL/1024);
>> RSSI_dBM = (int8_t) ((-50.0 * V_RSSI) - 45.5);
>>
>>
>> Where V_RSSI and RSSI_VAL are of type double.  Using this I'm getting 
>> a value of around 200, which is much higher than the range I'd 
>> expect.  Does anyone know what data types I could use to locally 
>> compute this?
>>
>> Thanks for any replies.
>>
>> - Sean
>>
>>
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>
>