Hi Terry
On 06/06/18 15:44, Terry Coles wrote:
I'm not sure that I understand that. My 1-Wire Temperature Sensors (https://
www.amazon.co.uk/gp/product/B00HCB8GLU/ref=oh_aui_detailpage_o01_s00?
ie=UTF8&psc=1) only have three wires; +3.3 V, 0 V and data. When I connect
them to my Pi I can read the temperature without any messing with pulse
generation or measurement.
That's fine - whoever has written the 1-Wire interface driver software
will have needed to mess with those things.
I can see that if we wanted to design the interface in discrete components or
low-level logic, we would probably need to think about such things, but even
we aren't daft enough to try that :-) What we need is the 1-Wire interfacing
components that are integrated into the DS18B20.
I wasn't suggesting that, only implementing the 1-Wire driver code on
the Pi, but I gather that's all been done.
In terms of multiplexing several Hall effect sensors, you could use a
PISO shift register (eg 74HC165) and clock the bits out as with SPI.
For longer distances, I'd suggest a single chip micro to read the Hall
devices and send the data over asynchronous serial (RS232, RS485 etc).
An MC9S08SH8 is available in DIL package and a USBDM programmer can be
bought on Ebay for around £20.
We are happy with getting the bits into serial and have considered several
designs. We've got to the point of deciding the best interfacing technique at
the moment. Currently we are prototyping a system using I/O expander chips
and I2C. If that throws up problems then we'll look at SPI, 1-Wire or
RS232/422/485 and whatever logic we need to get the bits to the bus.
Looks like Ralph has located what you were looking for!
Cheers
Tim
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