<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body >I have these level shifters, https://anibit.com/product/ptt02004<div><br></div><div>4 channels, but they are compact and less than half the cost of the adafruit 8 channel. I could bring some to tonights meeting, though I'm not allowed to sell stuff in the meeting, so we would have to meet in the parking lot.</div><div><br></div><div>Check out the docs and description to see if they would work for your case, but it sounds to me like they would.</div><br><br><div>-------- Original message --------</div><div>From: Carl Nobile <carl.nobile@gmail.com> </div><div>Date:08/11/2014 10:41 AM (GMT-05:00) </div><div>To: Jeff Highsmith <jeff@jeffhighsmith.com> </div><div>Cc: triembed@triembed.org </div><div>Subject: Re: [TriEmbed] Question For Meeting Tonight </div><div><br></div><div dir="ltr">Brian,<div><br></div><div>Adafruit has an 8 channel level converter for $8.00 ea. The reason that you need a level converter is that the <font face="arial, sans-serif">MCP23017 is not supposed to work on 3.3V, it does in some situations, but is bad practice to do it, as it will cause some weird issues at times--like using an external power source.You can make a level converter out of a bunch of 2N7000 MOSFETSs, but this will cost you more in money and time.</font></div>
<div><br></div><div><a href="http://www.adafruit.com/products/395?gclid=Cj0KEQjw06GfBRCR9tDI4t6n5_MBEiQAFo6kuAZUlnzsKVp8bN5d3FFaA6C7nQnUfTtJBW3DTIYfAi0aAuOW8P8HAQ">http://www.adafruit.com/products/395?gclid=Cj0KEQjw06GfBRCR9tDI4t6n5_MBEiQAFo6kuAZUlnzsKVp8bN5d3FFaA6C7nQnUfTtJBW3DTIYfAi0aAuOW8P8HAQ</a></div>
<div><br></div><div>Carl</div><div><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Aug 11, 2014 at 10:33 AM, Jeff Highsmith <span dir="ltr"><<a href="mailto:jeff@jeffhighsmith.com" target="_blank">jeff@jeffhighsmith.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div>Brian,</div><div><br></div><div>I propose for consideration a third option, power the MCP23017 from the 5V rail and use an i2c-safe level converter ( <a href="https://www.adafruit.com/products/757" target="_blank">https://www.adafruit.com/products/757</a> ) to connect your Pi to the i2c bus. This would scale well, if needed, as you could keep hooking up more MCP23017 chips to the 5V i2c bus.</div>
<div><br></div><div>Don't forget to connect the grounds of your 5V and 3V3 buses together. </div><span class="HOEnZb"><font color="#888888"><div><br><div><span>Jeff :)</span></div><div><span><br></span></div></div></font></span><div>
<div class="h5"><div><br>On Aug 11, 2014, at 10:11, Grawburg <<a href="mailto:grawburg@myglnc.com" target="_blank">grawburg@myglnc.com</a>> wrote:<br><br></div><blockquote type="cite"><div><span>Many of you are aware of my traffic light project with the Raspberry Pi. I currently have 12 LEDs that are connected to the Pi through an MCP23017 I/O port expander. The Pi provides 3.3 VDC to the LEDs with 470 ohm current-limiting resistors. This combination works just fine (I'll have it with me tonight.) But I want to also make a set-up that uses an external 5 VDC to power the LEDs; I will still use the MCP23017 to provide the additional output pins. There are two options I am aware of and would like some comments tonight.</span><br>
<span></span><br><span>1. Use 12 2N3904 transistors (with appropriate resistors)</span><br><span>2. Use three 4-channel LTV-847 opto-couplers (also with appropriate resistors)</span><br><span></span><br><span></span><br><span></span><br>
<span></span><br><span>Thanks,</span><br><span>Brian Grawburg</span><br><span></span><br><span></span><br><span></span><br><span></span><br><span>_______________________________________________</span><br><span>Triangle, NC Embedded Computing mailing list</span><br>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br>-------------------------------------------------------------------------------<br>Carl J. Nobile (Software Engineer)<br><a href="mailto:carl.nobile@gmail.com">carl.nobile@gmail.com</a><br>
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