----- Original Message ----- 
From: "ThePicMan" <thepicman@infinito.it>
Subject: [EE] Poor man's very low frequency oscilloscope.


> 2) Use a full MAX232 or some diode/transistor-based hack? Consider

> 4) Would it be wise to power everything off the PC's RS232? Together

If you are always going to use the SAME PC, then use your transistor hack
and power it from the serial port.

Keep in mind that serial ports are becoming extinct, and perhaps more
frustrating, there is wide variation in PC serial ports.  I did a survey
about a year ago and serial port voltages range from +/- 15 (which used to
be the standard) to +/- 0.9 (!). On some ports, anything below about +0.7
will be counted as negative, on others, you need to get below -5.  The
MAX232 is simple and will get you a nice swing that will work with about
anything.  The transistor probably is already sitting in your parts drawer,
but what works with your current PC might not work with the next, if it even
has a serial port.

Ditto for the power.  Most PCs seem to put out about 9 volts, but much lower
voltages aren't uncommon.  If you power your circuit from the port, be
prepared for some nasty surprises from the next PC you try it on.

--McD



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