[TriEmbed] "Latching" device

Glen Smith mrglenasmith at gmail.com
Thu Apr 10 08:20:00 CDT 2014


A set reset latch will do just what you are asking for. You can build your
own with cross coupled Nand gates or you can plop down a ready made one.
The 74LV00 is a 3.3v quad Nand in a 14 pin DIP. With this you can make 2
S-R latch's.

Digikey has the  74LVC574 available for $0.59 each in 20 pin DIP which gets
you 8 of them in a pack.
http://www.digikey.com/product-detail/en/SN74LVC574AN/296-12910-5-ND/476078

Glen


On Thu, Apr 10, 2014 at 8:55 AM, Grawburg <grawburg at myglnc.com> wrote:

> I'm making a traffic light project for the Raspberry Pi using an MCP23017
> port expander. The Python code works fine and lights up the
> 6 LEDs in the correct pattern. Now I want to add some other features and
> need a way to "latch" a device that is connected to one of the
> input pins on the MCP when I press a push button. It needs to remain high
> until specifically set low by a Python command. Perhaps there is
> some type of solid state device (3.3 VDC) that will function in this
> manner.
>
>
> Brian Grawburg
> Wilson
>
> --
> I use Opera Web Browser.
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