AVR-Chat

Hi Folks,

I need to read an 8 switch dip switch but I only have 3 inputs left. 
I'm using 2 AAA batteries for this project so I need to use low
voltage/low power parts.  Anybody have any good ideas?

Thanks again,

Richard Cooke

Unfortunately I can't.  I don't have the space in this design and I
need to make it as easy as possible for the end user to make their
selection.  This limits me to a dip switch that can be switched with a
pencil or finger nail.  I can't expect them to have a screwdriver
handy.  I also don't have the room for a rotary knob.

Richard Cooke

--- In AVR-Chat@yahoogroups.com, "Cat" <catalin_cluj@...> wrote:

>
> Can you use a BCD switch? All done for you.
> 
> Cat
> ----- Original Message ----- 
> From: "Richard Cooke" <rcooke@...>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Sunday, June 24, 2007 4:29 PM
> Subject: [AVR-Chat] 8 to 3 demultiplexer?
> 
> 
> > Hi Folks,
> > 
> > I need to read an 8 switch dip switch but I only have 3 inputs left. 
> > I'm using 2 AAA batteries for this project so I need to use low
> > voltage/low power parts.  Anybody have any good ideas?
> > 
> > Thanks again,
> > 
> > Richard Cooke
> > 
> > 
> > 
> > 
> > Yahoo! Groups Links
> > 
> > 
> > 
> >
>

Can you use a BCD switch? All done for you.

Cat
----- Original Message ----- 

From: "Richard Cooke" <rcooke@digitalwavelength.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Sunday, June 24, 2007 4:29 PM
Subject: [AVR-Chat] 8 to 3 demultiplexer?


> Hi Folks,
> 
> I need to read an 8 switch dip switch but I only have 3 inputs left. 
> I'm using 2 AAA batteries for this project so I need to use low
> voltage/low power parts.  Anybody have any good ideas?
> 
> Thanks again,
> 
> Richard Cooke
> 
> 
> 
> 
> Yahoo! Groups Links
> 
> 
> 
>

A 74HC165 perhaps?

On 24 Jun 2007 at 22:29, Richard Cooke wrote:

> Hi Folks,
> 
> I need to read an 8 switch dip switch but I only have 3 inputs left. 
> I'm using 2 AAA batteries for this project so I need to use low
> voltage/low power parts.  Anybody have any good ideas?
> 
> Thanks again,
> 
> Richard Cooke
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
>

At 10:29 PM 6/24/2007 +0000, you wrote:
>Hi Folks,
>
>I need to read an 8 switch dip switch but I only have 3 inputs left.
>I'm using 2 AAA batteries for this project so I need to use low
>voltage/low power parts.  Anybody have any good ideas?

A priority encoder such as 74x148?  Encodes the highest priority switch 
into a 3 bit value.  Basically the inverse of a '138

Robert

http://www.aeolusdevelopment.com/

 From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time?  37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live.... we 
currently have stock."

Has anybody mentioned using a 74x165?  8 parallel in, serial out?
Load, shift, data: 3 pins.

Robert Adsett wrote:
> At 10:29 PM 6/24/2007 +0000, you wrote:
>> Hi Folks,
>>
>> I need to read an 8 switch dip switch but I only have 3 inputs left.
>> I'm using 2 AAA batteries for this project so I need to use low
>> voltage/low power parts.  Anybody have any good ideas?
> 
> A priority encoder such as 74x148?  Encodes the highest priority switch 
> into a 3 bit value.  Basically the inverse of a '138
> 
> Robert


-- 
erikc
--
GILLETTE'S PRINCIPLE: "If you want to make people angry, lie. If
you want to make them absolutely livid with rage, tell the
truth."

Three dip-switches and a binary table for the user?

On 24 Jun 2007 at 22:41, Richard Cooke wrote:

> Unfortunately I can't.  I don't have the space in this design and I
> need to make it as easy as possible for the end user to make their
> selection.  This limits me to a dip switch that can be switched with a
> pencil or finger nail.  I can't expect them to have a screwdriver
> handy.  I also don't have the room for a rotary knob.
> 
> Richard Cooke
> 
> --- In AVR-Chat@yahoogroups.com, "Cat" <catalin_cluj@...> wrote:
> >
> > Can you use a BCD switch? All done for you.
> > 
> > Cat
> > ----- Original Message ----- 
> > From: "Richard Cooke" <rcooke@...>
> > To: <AVR-Chat@yahoogroups.com>
> > Sent: Sunday, June 24, 2007 4:29 PM
> > Subject: [AVR-Chat] 8 to 3 demultiplexer?
> > 
> > 
> > > Hi Folks,
> > > 
> > > I need to read an 8 switch dip switch but I only have 3 inputs left. 
> > > I'm using 2 AAA batteries for this project so I need to use low
> > > voltage/low power parts.  Anybody have any good ideas?
> > > 
> > > Thanks again,
> > > 
> > > Richard Cooke
> > > 
> > > 
> > > 
> > > 
> > > Yahoo! Groups Links
> > > 
> > > 
> > > 
> > >
> >
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
>

----- Original Message ----- 

From: "Richard Cooke" <rcooke@digitalwavelength.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Sunday, June 24, 2007 11:29 PM
Subject: [AVR-Chat] 8 to 3 demultiplexer?


> Hi Folks,
> 
> I need to read an 8 switch dip switch but I only have 3 inputs left. 
> I'm using 2 AAA batteries for this project so I need to use low
> voltage/low power parts.  Anybody have any good ideas?

You could use a shift register, like the 74HC165.

Leon
--
Leon Heller
Amateur radio call-sign G1HSM
Yaesu FT-817ND and FT-857D transceivers
Suzuki SV1000S motorcycle
leon355@btinternet.com
http://www.geocities.com/leon_heller

--- In AVR-Chat@yahoogroups.com, "Richard Cooke" <rcooke@...> wrote:
> I need to read an 8 switch dip switch but I only have 3 inputs left. 
Take a look at the PCF7854 I/O expander (standby current is 10uA).  It 
has an I2C interface and implements 8 I/O lines.  If you already are 
using other I2C devices it won't require any additional I/O lines on 
the AVR.  If you aren't, it only takes 2 I/O lines, preferably SDA and 
SCL.  If those pins are already irretrievably commited, any two I/O 
pins will do if you have the space for the code to bit bang the I2C 
protocol.

Don Kinzer
ZBasic Microcontrollers
http://www.zbasic.net

--- In AVR-Chat@yahoogroups.com, "Don Kinzer" <dkinzer@...> wrote:
> Take a look at the PCF7854 I/O expander [...]

Sorry, that should be PCF8574 or PCF8574A.  The only difference 
between the two is the slave address.

Don Kinzer
ZBasic Microcontrollers
http://www.zbasic.net

> I need to read an 8 switch dip switch but I only
> have 3 inputs left. 
> I'm using 2 AAA batteries for this project so I
> need to use low voltage/low power parts.
> Anybody have any good ideas?

You can use several approaches:
1) Diode matrix with pull up resistors as a 8 to 3
decoder. Use schottky diodes to keep VL within 0.3V.
2) If ADC lines are available, use a resistor network
to sense several keys from one line while keeping a
respectable noise margin. Will also detect multiple
key presses.
3) I2C or SPI ICs (see maxim site) which have a
working range of 2.5 - 5.5V.
4) If some of the output lines could briefly be
switched without disturbing the circuit (say while the
ENABLE signal is unasserted as in the case of LCD
bus), connect those lines via a (schottky) diode and
the switches to a common input line. The input line
should be pulled to inactive state when the switches
are OFF by a suitable resistor.
5) Are 8 switches *really* required? Will combinations
of switches or a menu based approach not work? Will a
BCD switch work?

Cheers,
Samir.


       
____________________________________________________________________________________
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You all have given me a bunch of valid options - thank you.  I think
the best fit for my application will be the 8-to-3 priority encoder. 
It's not too expensive and it works down to 2 volts.

Richard Cooke

--- In AVR-Chat@yahoogroups.com, Samir Lohani <slohani90182@...> wrote:
>
> > I need to read an 8 switch dip switch but I only
> > have 3 inputs left. 
> > I'm using 2 AAA batteries for this project so I
> > need to use low voltage/low power parts.
> > Anybody have any good ideas?
> 
> You can use several approaches:
> 1) Diode matrix with pull up resistors as a 8 to 3
> decoder. Use schottky diodes to keep VL within 0.3V.
> 2) If ADC lines are available, use a resistor network
> to sense several keys from one line while keeping a
> respectable noise margin. Will also detect multiple
> key presses.
> 3) I2C or SPI ICs (see maxim site) which have a
> working range of 2.5 - 5.5V.
> 4) If some of the output lines could briefly be
> switched without disturbing the circuit (say while the
> ENABLE signal is unasserted as in the case of LCD
> bus), connect those lines via a (schottky) diode and
> the switches to a common input line. The input line
> should be pulled to inactive state when the switches
> are OFF by a suitable resistor.
> 5) Are 8 switches *really* required? Will combinations
> of switches or a menu based approach not work? Will a
> BCD switch work?
> 
> Cheers,
> Samir.
> 
> 
>        
>
____________________________________________________________________________________

> Sick sense of humor? Visit Yahoo! TV's 
> Comedy with an Edge to see what's on, when. 
> http://tv.yahoo.com/collections/222
>