You're getting the level of a sine waveform. Do you really need to use an RMS detector.
I'm not familiar with this particular pic.Most of them come with at least a 10bit ADC.
You can sample the peak of the sine and convert to equivalent RMS.
Even a cheap peak detector would work for this. Or generate a quadrature from the fundamental and zero crossing detector to trigger ADC.
Maybe a cheaper way would use a auto-scaling DVM IC and drive relays to affect input attenuator instead of the display. Or even cheaper would be an attenuator built around the multi-comparitors in the LM3914.
THx-RNMarsh
PIC16F688 Digital Voltmeter - Electronics-Lab
http://www.kitelectronica.com/2016/02/tutorial-ic-lm3914-lm3915.html
THx-RNMarsh
PIC16F688 Digital Voltmeter - Electronics-Lab
http://www.kitelectronica.com/2016/02/tutorial-ic-lm3914-lm3915.html
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Dare I ask how fast this thing switches between levels? What will a soundcard see if the input goes from 0V to a 140Vp 20KHz sinewave?
Attenuation rate is about 100dB per second. But the output is limited to a safe value so such a step won't be a problem.
Jan
Another milestone in the development of the autoranger!
Finalised and tested the cal procedure.
Especially calibrating the freq response for 0.1dB flatness out to 100kHz is a challenge if you don't have a fully equipped lab
I now have a procedure that needs only an AC DMM with reasonable performance and a signal generator that can output 10kHz and 100kHz, preferably up to 10V or more but that's not critical.
The procedure directs you to do some measurements and enter values in a small spreadsheet and the spreadsheet then tells you what to adjust (cap trimmer) for which DMM indication.
For -20dB and -40dB settting, in both SE and BAL mode.
It's done faster than described!
Jan
Finalised and tested the cal procedure.
Especially calibrating the freq response for 0.1dB flatness out to 100kHz is a challenge if you don't have a fully equipped lab
I now have a procedure that needs only an AC DMM with reasonable performance and a signal generator that can output 10kHz and 100kHz, preferably up to 10V or more but that's not critical.
The procedure directs you to do some measurements and enter values in a small spreadsheet and the spreadsheet then tells you what to adjust (cap trimmer) for which DMM indication.
For -20dB and -40dB settting, in both SE and BAL mode.
It's done faster than described!
Jan
Attachments
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I have to decide how to get this out to people who want it. Probably as a kit, PCBs, box and a BoM. Or maybe complete units.
I have to count all the bits and parts see how much it will actually cost. As a complete unit it will be close to $300 for sure. The box and PCBs as a kit will be much lower of course.
The box I have now is not painted and not labelled and I am thinking about getting in an order of painted and labelled boxes.
There are a lot of SMD parts but I have made sure the smallest is 0805 so still easy to solder.
Maybe Group Buy, maybe Kickstarter? If I get 100 made prices will drop considerably.
This is new territory for me,
Jan
Nope, still a big delta. No triggering features (think synchronous averaging), limited LF extension, no reference channel, etc...
Yes. An AP does all that. And is also about 40dB more expensive
Really?
Audio Precision System One | eBay
Audio Precision Portable One Plus P1P 10612 with Probe Self Test Passed | eBay
Audio Precision ATS 1 Audio Test System | eBay
Prices for second hand lab equipment dropped well under 50% (more like 70% on average) in the last 12 months.
Of course, the fun of building something yourself is priceless.
P.S. And still available:
http://www.ebay.com/itm/Audio-Preci...425967?hash=item3d225b7c2f:g:cDAAAOSwRgJXiPzH
http://www.ebay.com/itm/Audio-Preci...252066?hash=item4d496b52a2:g:xU0AAOSw0UdXqibU
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