[TriEmbed] Question For Meeting Tonight

[Jon Wolfe]

I have these level shifters,   https://anibit.com/product/ptt02004

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.

Check out the docs and description to see if they would work for your case, but it sounds to me like they would.

<div>-------- Original message --------</div><div>From: Carl Nobile <carl.nobile at gmail.com> </div><div>Date:08/11/2014  10:41 AM  (GMT-05:00) </div><div>To: Jeff Highsmith <jeff at jeffhighsmith.com> </div><div>Cc: triembed at triembed.org </div><div>Subject: Re: [TriEmbed] Question For Meeting Tonight </div><div>
</div>Brian,

Adafruit has an 8 channel level converter for $8.00 ea. The reason that you need a level converter is that the 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.

http://www.adafruit.com/products/395?gclid=Cj0KEQjw06GfBRCR9tDI4t6n5_MBEiQAFo6kuAZUlnzsKVp8bN5d3FFaA6C7nQnUfTtJBW3DTIYfAi0aAuOW8P8HAQ

Carl



On Mon, Aug 11, 2014 at 10:33 AM, Jeff Highsmith <jeff at jeffhighsmith.com> wrote:
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




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Carl J. Nobile (Software Engineer)
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