Re: 1-wire to USB converter that can use 1820s directly

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Wed, 19 Apr 2006 09:08:24 +1000, "Rod Speed" <rod.speed.aaa@xxxxxxxxx>
wrote in message  <4al9ruFt6fgiU2@xxxxxxxxxxxxxx>:

>Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote
>> Rod Speed <rod.speed.aaa@xxxxxxxxx> wrote
>>> Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote
>
>>>> 5) Despite what OP writes, Dr Anderson's site does indeed
>>>> include schematics and explanations for the devices in question.
>
>>> Maybe you could post the precise url for the schematic for say
>>> http://www.phanderson.com/tm128/tm128.html
>
>> Sure:
>
>Nope.
>
>> here's the interconnect diagram:
>> http://www.phanderson.com/tm128/tm128_config.jpg
>
>Not the schematic, you cant see how he's
>powering the 1wire strings from that.

If one connects pin 3 of a  DS18x20 to V+, the chips are powered; if not,
they run in parasitic mode..

The diagram shows *clearly* that pin three of the "DS18S20 or DS18B20 or
DS1822" is connected to the wire that interconnects "Pin 1 GND" on the
DS2438 to "Black (GRD) " on the TM # 128. And that position 5 on the #128
connector is "Black ground".

So the two channels are being powered by data lines on pin 2 in parasitic
mode, not by V+ on pin 3. There are also 4.7k resistors in series with the
PIC data lines to protect the PIC.

... Marc
Marc_F_Hult
www.ECOntrol.org