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<div class="moz-cite-prefix">I'm going to disagree with sing
opto-isolators. They are slow (non-squarewave forming, but very
rounded waves) and very noisy (interference with PWM signals, and
mis-triggers for other I/O).<br>
<br>
I really like the solution provided in the pair of articles in
Circuit Cellar magazine, August & September. Basically he
uses a separate higher voltage, higher current power supply
suitable for driving motors, solenoids and any other loads you
might want. Then use a 5V regulator which connected to the R-Pi
GPIO pins 2 & 4 through a 0.74A fuse to supply power to the
R-Pi -- avoiding the proven delicate miniUSB-B power connector.<br>
<br>
Noting that the Gertboard uses level shifters, and you have to
know which direction the signal is going. Instead the author uses
a $1 dual-channel Si8421 isolator to buffer each pair of I/O
lines. Each side will operate with 2.7 to 5.5 V logic levels. He
also uses a bidirectional Si8602 isolator for pairs of
bidirectional I/O (like I2C). And these chips are far faster than
anything the R-Pi can produce. This will keep any back EMF or
other spikes generated by the I/O from working its way back
through to the R-Pi I/O pins, and offer the ability to drive
regular signals while not hurting the R-Pi. Note that the outputs
should have similar specs to those in an AVR chip (Arduino),
depending on which digital isolator you use. That should be
enough to drive a MOSFET or Darlington pair directly.<br>
<br>
I just noticed that Analog Devices makes 6-channel digital
isolators for around $2. (ADuM_764x)<br>
<br>
On 09/26/2013 10:41 AM, John Vaughters wrote:<br>
</div>
<blockquote
cite="mid:1380206509.11295.YahooMailNeo@web163005.mail.bf1.yahoo.com"
type="cite">
<div style="color:#000; background-color:#fff; font-family:arial,
helvetica, sans-serif;font-size:12pt"><br>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
'times new roman', 'new york', times, serif; background-color:
transparent; font-style: normal;">Also, on the power control
discussion, one of the best circuit protection plans is to use
opto-isolators. I did not see that mentioned. The basic
concept is you only power an led witch turns on a photo
transistor, which completely isolates your microprocessor from
back EMF issues. This does not protect the other circuit from
back EMF, so you still need to deal with it, but usually those
components are not as sensitive. Here is the best Motor
H-Bridge design I have found and it is entirely controlled
through opto-isolators. </div>
</div>
</blockquote>
<br>
<pre class="moz-signature" cols="80">--
Scott G. Hall
Raleigh, NC, USA
<a class="moz-txt-link-abbreviated" href="mailto:ScottGHall1@GMail.Com">ScottGHall1@GMail.Com</a>
</pre>
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