Low power ibutton reader/writer

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For orienteering, I'm considering building an ibutton device.
The runners carry a button (4096 bit NVRAM) and click into each
control point where their button gets the time at that control.
The final control has RS232 or other external comms to a laptop
which displays scores.

The control points need an battery powered MCU with piezo, LED
and possibly EEPROM attached via the 1-wire bus to a button socket.

The question is, what's the minimum power required to run the
control point? Is it possible (say with a small MSP-series) to
idle the reader in the uA range so it doesn't need a switch?

Can you point me to any published low-power ibutton designs?

Clifford Heath.


Re: Low power ibutton reader/writer
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Have you tried Maxim's web site?

A "standard" iButton reader should consume zero power until an ibutton is
connected.



Re: Low power ibutton reader/writer
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The info at Maxim's site seemed flooded with appnotes showing PC-based
readers, searches for "low power" turned up matches, but little relevant.
Thanks anyhow, I'll dig into the data sheets.


Re: Low power ibutton reader/writer
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I have some PIC drivers for the Dallas/Maxim Touch memory stuff hidden away
on CD. I am desperately searching for that CD now becasue I need one of the
designs I backed up to it. Email me at: a dot pearson at optusnet dot com
dot au and if I find it i will send the stuff to you. It has both loop
driven CRC and table driven CRC routines. Trade off between speed and
size...



Re: Low power ibutton reader/writer
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You can definitely do this with a PIC. I think the CCS C compiler
comes with a library for reading/writing to iButtons. I have to ask
where you are though? In the UK we are using two RF schemes one with
Atmel RFID chips. If you're in the UK I'd be interested to talk about
what you're doing - I know my club would be interested in cheap
control-site equipment so it's not the end of the world if it gets
stolen. Follow the links on our website and email sales.

Iain

Iain Tebbutt
www.claritech.co.uk - Hardware and Software Design

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