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

[Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Wed, 19 Apr 2006 03:29:50 GMT, Marc F Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>
wrote in message  <ebbb42tef1lcu4jfm6ldm1a9qpenqso0ac@xxxxxxx>:

>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.
>

Not sure why my fingers wrote the last sentence. The 4.7k resistors are
pullups to V+ (from the output to 5vdc).

... Marc
Marc_F_Hult
www.ECOntrol.org