Electronics > Beginners

9-bit Addressable Latch Required

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Docara:
Hi,

I'm using 3 Piezo Switches with RGB LEDs included. The LED's resistors are part of the assembly and the whole device is rated for 12V.

I would like to have individual control over each of these LEDs via uC but I cannot multiplex them in the usual way because they are too dim in operation and so I need them on 'statically'

The only way I can think off to is a 9-bit addressable latch (8-bit + 4-bit in practice) and just have the uC use 4 I/O pins for the addresses and 1 I/O pin for the data.

1. Is there an alternative (better) way to do this
2. Just to confirm - the output would always be present

Thanks
Matt

JS:
9 bits on a single chip seems odd, pcf8574 is an adressable latch, active high, hi-z low (works as input when low) 8 IO pins, you would only need 2 pins on the micro to drive up to 8 of them, I2C control so adress is selected in the data bus, no external chip select. Pretty common and modules come with those to test as they are used to drive lcd displays and is a very versatile chip.

If you need a single chip a 9 bit shift register would do what you nees but it could generate some flikker as you load the data to it. Or a 16 bit serial to parallel converter. I don't know any 9 bits converter...




JS

Docara:
Hi JS,

I know you cant get a 9-bit addressable latch,  I need one - that's my problem!

Please read my post again I've suggested an 8 and 4

The I2C port expander route  looks an interesting direction to pursue

Thanks
Matt

JS:
I saw that, but using 2 different ICs for the same task seems odd, and if you are short of pins you can probably use some of those extra 7 anyway, and the ones I said can be used as IO. I2C would be my first choice, even more olif you are counting your pins. 1 wire might hafe some solutions but I2C is the most obvious one to go.

JS

Docara:
The 16bit version (PCF8575) I think is a viable alternative, unfortunately it's only rated for 5V output so Tranny's will be needed.



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