[sdiy] Measuring Vpp

[Oren Leavitt]

On 6/11/2014 6:58 PM, Nicholas Keller wrote:
> John,
>
> Thanks for your suggestion, but that won't work for my scope.  The screen is tiny and digital with poor resolution.  I need an option that does not require the use of a scope, unless it is software-based and can utilize my sound card for signal input.
>
> Nick
>

Hi Nick,

Another possibility is a simple level indicator circuit made of two 
comparators and two LEDs - one set at -5V, one set at +5V.


>
> On Jun 11, 2014, at 7:43 PM, John Speth <jspeth at avnera.com> wrote:
>
>>> The scope I have isn't great, more just for visual display of waveform
>> than
>>> accurate measurements.   I can't afford to get a proper scope, so I'm
>> looking
>>> for another way to calibrate outputs to 10Vpp and 20Vpp.  I looked up
>> how to
>>> do it with a DMM and it seemed more complicated than I had hoped. Does
>> anyone
>>> here have a suggestion of how to do this (easily) using a DMM, decibel
>>> levels, or freeware?
>>
>> A calibrated scope is nothing more than knowing the voltage difference
>> between graticule hash marks.  You can calibrate that yourself with a
>> known reference voltage for vertical and a known clock for horizontal
>> (time).
>>
>> The voltage reference can be attained by getting a voltage reference IC,
>> wiring it up, and sending the voltage to your scope.  Then use some tape
>> with carefully drawn hash marks.  Stick the tape to your scope screen and
>> adjust your vertical gain so that you get a nice calibrated scale (for
>> example, 1V per division).  Now you have a calibrated scope.  You'll need
>> to recalibrate every time the vertical gain changes and maybe even every
>> time you turn on your scope.  Be sure to verify your reference with your
>> DMM for sanity.  You might need an op-amp circuit to gain up your
>> reference voltage.
>>
>> JJS
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