04-03-2009 01:26 PM
Hi,
I have attached a screenshot of the time domain waveform graph. If I'm not wrong, the signal displayed is from the onboard microphones of SPEEDY-33 in digitize value. The peak amplitude is 557 and the rms value is 236.23 (and the values look wierd). Hence, how do I convert back to analog input value measured in mV?
Please advise. Thanks!
Regards,
Bee Kwang
04-05-2009 11:21 PM
Hi,
What is the unit of '557' you have obtained. Find the output from speedy manuals. Having given the unit of the output obtained it is possible to figure the conversion method.
04-06-2009 03:18 AM
04-06-2009 04:43 AM
The SPEEDY-33 User manual did not state much information except that it support either onboard microphone or line-in input via the jumper settings. It support 16-bit A/D and sampling freq of 8, 18, 24, 36 and 48KHz.
I guess the "557" should be the digitize value (level) of the "analog volt" measured by the microphone. The maximum given voltage of the input is given as 600mV.
Can I assume that
65535 levels = 600mV
1 level = 600mV / 65535
557 = 557 x (600mV/65535) = 0.005mV?
04-06-2009 05:04 AM
Hi guys,
I found something new >> http://digital.ni.com/public.nsf/allkb/073133DA607E702A86256FE8007A8D79?OpenDocument
The link mentioned that the analog output amplitudes from –32,768 to 32,767 (digitize value?) corresponds to approximately ±1.5 volts. This 1.5 volts is refering to the maximum working voltage for analog outputs on page A-1 of the data sheet.
04-06-2009 05:28 AM
BK Lian wrote:peak amplitude from graph X (each digitize step value)
= peak amplitude from graph X (1.2/65535)Thanks!
Yes this is correct. Have you tried to hook up your bord to a signal generator. This way you can check if the ADC works as expected
04-06-2009 05:47 AM
04-06-2009 05:53 AM
04-06-2009 06:29 AM
Yup, previously I've checked with the NI support engineer, the flow is input sound >> 1) microphone with buid-in gain >> 2) op-amp >> 3) ADC >> 4) LabVIEW.
Hence, the maxi working analog input voltage of 600mV is refering to which stage (before 1 or after 2)? Also, what is the typical voltage from a microphone?
04-06-2009 08:10 AM
BK Lian wrote:Yup, previously I've checked with the NI support engineer, the flow is input sound >> 1) microphone with buid-in gain >> 2) op-amp >> 3) ADC >> 4) LabVIEW.
Hence, the maxi working analog input voltage of 600mV is refering to which stage (before 1 or after 2)? Also, what is the typical voltage from a microphone?
Actually non of the above. 600mV is the max input level for the analog input channels.