Re: 24 Volt 1-Wire dry contact relay??

Across the coil because that's where the 2406 will be connected.

Coils (inductors) produce a voltage proportional to the rate of change 
of current going through it.  Switching on and off a voltage source to 
the coil produces a high rate of change of current -- imagine the 
current going from zero (or some value, "I") to some value "I" (or 
zero).  This is a "step", and has a very high rate of change in the 
transition.  Hence, a relatively large voltage will be produced by the 
coil (opposite to the voltage applied).  The diode will provide a path 
for the current produced by this voltage so that it doesn't go through 
the 2406.

The direction the diode is connected is very important.  In the 
schematic, the arrow tip in the diode symbol should be attached to the 
plus (+) end of the coil, and the other end to the ground (or -ve end 
of the coil).

Hope that provides some clarity.

	-Shawn

On 23-Jun-04, at 7:04 PM, Matt Chapman wrote:

> Should the diode be connect across the relay load or the
> relay coil?
>
> Thanks,
>
>   - Matt
>
>
> Kelly Smith wrote:
>
>> All - And be sure to add a "back-EMF kickback" diode strapped across 
>> the
>> relay, or you will blow out the DS2406 on the 8x1-Wire board (cathode 
>> goes
>> to the relays +V).
>> Best regards, Kelly Smith
>> -----Original Message-----
>> From: tini-admin-6tN4nzCoH/[email protected] [mailto:tini-admin-6tN4nzCoH/[email protected]]On Behalf 
>> Of
>> Bruce Boyes
>> Sent: Wednesday, June 23, 2004 9:59 AM
>> To: Joel Rowley
>> Cc: tini-6tN4nzCoH/[email protected]
>> Subject: Re: [TINI]24 Volt 1-Wire dry contact relay??
>> At 06:52 PM 6/22/2004 -0400, Joel Rowley wrote:
>>> Hey List,
>>>
>>> I am looking for a 24 Volt 1-Wire dry contact relay.  What I mean by 
>>> this
>>>
>> is
>>> that the relay can handle 24 volts going through it, not that the 
>>> relay is
>>> powered by 24 volts.  Do any of you know if there is something like 
>>> that
>>>
>> out
>>> there or not?
>>>
>> You can purchase these at DigiKey and connect them to an 8x1 Wire 
>> board as
>> long as the relay coil can be powered by 12 volts or less at 50 mA or 
>> less
>> so that it can be driven by PIOA from a DS2406.:
>> http://www.systronix.com/expansion/8x1wire/81w.htm
>> and
>> http://www.systronix.com/expansion/8x1wire/DS2406_relay_drive.pdf
>> Regards
>> Bruce
>>> Thanks!
>>> Joel Rowley
>>>
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