<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div style="" class="" id="yui_3_16_0_1_1428723133426_3699">Hi Dwight,</div><div style="" class="" id="yui_3_16_0_1_1428723133426_4246"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_4247" dir="ltr">How much speed do you need. :-)<br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_4129"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3029" dir="ltr">The
primary purpose of an oscilloscope is to capture / show a signal. The
scope must be fast enough to capture the highest frequency of interest
in the signal. Advanced triggering modes and deep buffers are great but
they are lipstick on a pig unless the basic mechanism is up to the
task.<br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3028" dir="ltr"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3027" dir="ltr">If
you are looking at a pure sinusoid, the needed -3dB Bandwidth is the
frequency of the sinusoid, but most interesting signals consist of a
fundamental and an assortment of harmonics. The highest frequency
harmonic of interest is the driver. In analog applications, the fastest
frequency is often implied by the application or governing body.
Digital applications are a bit different. The key parameter is the
clock edge's rise time (time required for the driver to charge the line
from 10% of the rail to 90% of the rail). Ideal clocks (zero rise time)
have inifinite bandwidth, but they don't exist outside text books.
-3 dB Bandwidth of periodic pulse trains (clocks) is often estimated by 0.35 /
rise time.</div><div id="yui_3_16_0_1_1428723133426_5688" style="" class="" dir="ltr"><br></div><div id="yui_3_16_0_1_1428723133426_5689" style="" class="" dir="ltr">(- 3dB Bandwidth means a signal of that frequency is attenuated by -3dB (voltage is reduced by about 30%, power by 50%) before it is digitized. Attenuation increases rapidly with frequency)<br></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3615" dir="ltr"><br style="" class=""></div>Slow Ex.<div style="" class="" id="yui_3_16_0_1_1428723133426_3428" dir="ltr"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3716" dir="ltr">5 ns edge (10% to 90% rise time)</div><div style="" class="" id="yui_3_16_0_1_1428723133426_3292" dir="ltr">Bandwidth = 0.35 / 5 ns = 70 MHz</div><div style="" class="" id="yui_3_16_0_1_1428723133426_3717" dir="ltr"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3718" dir="ltr">Fast Ex.</div><div style="" class="" id="yui_3_16_0_1_1428723133426_3719" dir="ltr"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3720" dir="ltr">200 ps edge</div><div style="" class="" id="yui_3_16_0_1_1428723133426_3721" dir="ltr">Bandwidth = 0.35 / 200 ps = 1.75 GHz!</div><div style="" class="" id="yui_3_16_0_1_1428723133426_3930" dir="ltr">(This scope costs more than my car) :-)<br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3723" dir="ltr"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_3794" dir="ltr">There
is a close corollary to Bandwidth which is Sample Rate. It should be
at least 2 times the Bandwidth to meet Nyquist but 4 x Bandwidth gives
more comfortable margin. Sample rate can be enhanced in post processing
(after the AtoD converter) with repetitive signals so it is probably
not going to be the limiting factor for you. Bandwidth will trip you up
first because fast probes, preamps and converters are expensive and
can't be replaced after the fact with Digital magic. This is really the
heart of the instrument.<br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_4012"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_4117" dir="ltr">For
further information, spend some time at tektronix.com or agilent.com.
National Instruments (ni.com) also has some good whitepapers with
further information.</div><div style="" class="" id="yui_3_16_0_1_1428723133426_4118" dir="ltr"><br style="" class=""></div><div style="" class="" id="yui_3_16_0_1_1428723133426_4119" dir="ltr">Good luck,</div><div style="" class="" id="yui_3_16_0_1_1428723133426_3987" dir="ltr">Kevin Schilf</div><div id="yui_3_16_0_1_1428723133426_5817" style="" class="" dir="ltr">Digital Telesis, Inc.<br style="" class=""></div><div id="yui_3_16_0_1_1428723133426_5469"><span></span></div><br> <div id="yui_3_16_0_1_1428723133426_5473" style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div id="yui_3_16_0_1_1428723133426_5472" style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div id="yui_3_16_0_1_1428723133426_5471" dir="ltr"> <hr id="yui_3_16_0_1_1428723133426_5560" size="1"> <font id="yui_3_16_0_1_1428723133426_5470" size="2" face="Arial"> <b><span style="font-weight:bold;">From:</span></b> Dwight Morgan <dwight.w.morgan@gmail.com><br> <b><span style="font-weight: bold;">To:</span></b> Triangle Embedded Computing Discussion <triembed@triembed.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Friday, April 10, 2015 9:56 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> [TriEmbed] Oscilloscope Question<br> </font> </div> <div id="yui_3_16_0_1_1428723133426_5516" class="y_msg_container"><br><div id="yiv9575330733"><style><!--
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--></style><div id="yui_3_16_0_1_1428723133426_5515"><div id="yui_3_16_0_1_1428723133426_5514" class="yiv9575330733WordSection1"><div id="yui_3_16_0_1_1428723133426_5513" class="yiv9575330733MsoNormal">I’m thinking of getting an oscilloscope or a pc-based device that does that function like the NI MYDAQ. I’m not an electrical engineer, I just want to be able to look at what kind of wave form I’m getting for the small circuits I’m using or planning to use with Arduino and Raspberry Pi. Something with good instructions, ease of use, and inexpensive would be nice.</div><div class="yiv9575330733MsoNormal"> </div><div id="yui_3_16_0_1_1428723133426_5783" class="yiv9575330733MsoNormal">Any suggestions/comments are appreciated.</div><div class="yiv9575330733MsoNormal"> </div><div class="yiv9575330733MsoNormal">Thanks!</div><div class="yiv9575330733MsoNormal"> </div><div class="yiv9575330733MsoNormal">Dwight Morgan</div></div></div></div><br>_______________________________________________<br>Triangle, NC Embedded Computing mailing list<br><a ymailto="mailto:TriEmbed@triembed.org" href="mailto:TriEmbed@triembed.org">TriEmbed@triembed.org</a><br><a href="http://mail.triembed.org/mailman/listinfo/triembed_triembed.org" target="_blank">http://mail.triembed.org/mailman/listinfo/triembed_triembed.org</a><br>TriEmbed web site: <a href="http://triembed.org/" target="_blank">http://TriEmbed.org</a><br><br><br></div> </div> </div> </div></body></html>