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Topic: serially addressable digital mux (Read 696 times) previous topic - next topic

eriknyquist

Jan 23, 2013, 11:39 am Last Edit: Jan 23, 2013, 11:43 am by eriknyquist Reason: 1
I need a digital mux part with the following features (havent beeen able to find one, thought maybe somebody here knows of one);
 
   4-8 serially addressable switches
   2 inputs only-   [1]serial in (to select output) and     [2]the signal to be switched

does anybody know of a part that does this? surely there must be one out there somewhere!
see diagram below



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johnwasser

You could use two chips:  a counter to count the pulses and a multiplexer to select the output.
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eriknyquist

Yeah that maxim part was actually my first option, they're 6 bucks a pop though! this is for something I'll be manufacturing quite a few of, so unfortunately this solution has to be < 50c.

clock, yes I forgot to include a clock in that diagram, but a clock signal WILL be part of this setup....so are there any parts out there that let me do it with 3 lines? clock, signal, and serial (line select)

olof_n

Just an idé. You could use a cheap MCU instead of the expensive serial mux.

Atmega8 cost 0,88$ with free shipping.
http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=atmega8&_sacat=0&_from=R40

Would be easy to write code which read address and state from UART or I2C and toggle outputs.



eriknyquist

johnwasser- That's an interesting idea, could you elaborate any more on that? doesn't a counter just take a clock input, and have a single output? how could I control a mux with that?

Chagrin


johnwasser- That's an interesting idea, could you elaborate any more on that? doesn't a counter just take a clock input, and have a single output? how could I control a mux with that?


He meant that you could program the ATMega8 to act like a mux. It's just like adding another Arduino to your project to take over the mux duties.

An ATMega8 is just an older style of ATMega328. Same number of pins but less memory and a bit cheaper -- well, actually the ATMega328 is a bit cheaper if you buy it from domestic sources (Digikey/Mouser/Newark/etc.).

See: http://arduino.cc/en/Tutorial/ArduinoISP or http://0000b.blogspot.com/2010/09/using-atmel-atmega8-as-arduino.html or http://hlt.media.mit.edu/?p=1695


johnwasser


johnwasser- That's an interesting idea, could you elaborate any more on that? doesn't a counter just take a clock input, and have a single output? how could I control a mux with that?


It's not clear exactly what you want.  Did you want an ANALOG multiplexer or DIGITAL?  If DIGITAL, did you want 1 input and 8 outputs or 8 inputs and 1 output?

Let's assume analog.  Take a CMOS counter like the TI CD4024B  7-stage ripple counter and connect the low three bits to the address inputs of the TI CD4051BC "Single 8-Channel Analog Multiplexer/Demultiplexer".  Each pulse to the counter will select a different connection in the multiplexer. 

With CMOS you have to be sure to tie all unused inputs HIGH or LOW.  If an input is left floating it might turn on both of the Complimentary-symetry MOS transistors and try to drive a signal both HIGH and LOW.  This can burn out your chip.
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