[TriEmbed] Question For Meeting Tonight

[Jeff Highsmith]

Brian,

I propose for consideration a third option, power the MCP23017 from the 5V rail and use an i2c-safe level converter ( https://www.adafruit.com/products/757 ) 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.

Don't forget to connect the grounds of your 5V and 3V3 buses together. 

Jeff :)


> On Aug 11, 2014, at 10:11, Grawburg <grawburg at myglnc.com> wrote:
> 
> 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.
> 
> 1. Use 12 2N3904 transistors (with appropriate resistors)
> 2. Use three 4-channel LTV-847 opto-couplers (also with appropriate resistors)
> 
> 
> 
> 
> Thanks,
> Brian Grawburg
> 
> 
> 
> 
> _______________________________________________
> Triangle, NC Embedded Computing mailing list
> TriEmbed at triembed.org
> http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
> TriEmbed web site: http://TriEmbed.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20140811/35b5cc53/attachment.htm>