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From: "Jason Hotchkiss" <jason_hotchk...@hotmail.com>
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Subject: Re: [brighton-hacker-space] Protection diodes for relays
Date: Sat, 17 Nov 2012 22:36:51 -0000
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Hi Seb

so you you mean you have it attached without a transistor? I=E2=80=99m =
surprised the current sourced from the Arduino pin is good enough to =
energise a relay coil at all - but I don=E2=80=99t think it will be =
doing your Arduino any good, both from the =E2=80=9Con=E2=80=9D current =
draw and the high voltage flyback pulse when you turn the coil off

Without knowing any more about your setup, I think you should get both a =
diode and a transistor in there (like the diagram you linked)

Go for the highest current NPN switch transistor you can get. Even with =
a wimpy transistor like a 3904 you will at least be protecting the =
Arduino (the transistor will blow first)

Ideally get a darlington switch (uln280... tip120) or at worst something =
like a 2n2222

Cheers
Jason


From: Seb Lee-Delisle=20
Sent: Saturday, November 17, 2012 10:28 PM
To: brightonhackerspace=20
Subject: [brighton-hacker-space] Protection diodes for relays

Hi everyone! =20

We've attached a relay directly to an arduino pin and gnd, and I now =
gather that that's not a great thing to do :)=20

We'll be rebuilding the circuit (as in this diagram =
http://www.kpsec.freeuk.com/components/relay.htm#protect ) when I get =
back to Brighton, but in the meantime, can I protect the arduino using =
just a diode?=20

Any advice would be appreciated.=20

thanks!

Seb=20

--=20
You received this message because you are subscribed to the Google =
Groups "BuildBrighton - the Brighton Hacker Space" group.
To post to this group, send email to =
brightonhackerspace@googlegroups.com.
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<HTML><HEAD></HEAD>
<BODY dir=3Dltr>
<DIV dir=3Dltr>
<DIV style=3D"FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: 12pt">
<DIV>Hi Seb</DIV>
<DIV>&nbsp;</DIV>
<DIV>so you you mean you have it attached without a transistor? =
I=E2=80=99m surprised=20
the current sourced from the Arduino pin is good enough to energise a =
relay coil=20
at all - but I don=E2=80=99t think it will be doing your Arduino any =
good, both from the=20
=E2=80=9Con=E2=80=9D current draw and the high voltage flyback pulse =
when you turn the coil=20
off</DIV>
<DIV>&nbsp;</DIV>
<DIV>Without knowing any more about your setup, I think you should get =
both a=20
diode and a transistor in there (like the diagram you linked)</DIV>
<DIV>&nbsp;</DIV>
<DIV>Go for the highest current NPN switch transistor you can get. Even =
with a=20
wimpy transistor like a 3904 you will at least be protecting the Arduino =
(the=20
transistor will blow first)</DIV>
<DIV>&nbsp;</DIV>
<DIV>Ideally get a darlington switch (uln280... tip120) or at worst =
something=20
like a 2n2222</DIV>
<DIV>&nbsp;</DIV>
<DIV>Cheers</DIV>
<DIV>Jason</DIV>
<DIV>&nbsp;</DIV>
<DIV=20
style=3D"FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; =
COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: =
none">
<DIV style=3D"FONT: 10pt tahoma">
<DIV><FONT size=3D3 face=3DCalibri></FONT>&nbsp;</DIV>
<DIV style=3D"BACKGROUND: #f5f5f5">
<DIV style=3D"font-color: black"><B>From:</B> <A =
title=3D...@leedelisle.com=20
href=3D"mailto:s...@leedelisle.com">Seb Lee-Delisle</A> </DIV>
<DIV><B>Sent:</B> Saturday, November 17, 2012 10:28 PM</DIV>
<DIV><B>To:</B> <A title=3Dbrightonhackerspace@googlegroups.com=20
href=3D"mailto:brightonhackerspace@googlegroups.com">brightonhackerspace<=
/A>=20
</DIV>
<DIV><B>Subject:</B> [brighton-hacker-space] Protection diodes for=20
relays</DIV></DIV></DIV>
<DIV>&nbsp;</DIV></DIV>
<DIV=20
style=3D"FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; =
COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: =
none">Hi=20
everyone!&nbsp;=20
<DIV>&nbsp;</DIV>
<DIV>We've attached a relay directly to an arduino pin and gnd, and I =
now gather=20
that that's not a great thing to do :) </DIV>
<DIV>&nbsp;</DIV>
<DIV>We'll be rebuilding the circuit (as in this diagram <A=20
href=3D"http://www.kpsec.freeuk.com/components/relay.htm#protect">http://=
www.kpsec.freeuk.com/components/relay.htm#protect</A>=20
) when I get back to Brighton, but in the meantime, can I protect the =
arduino=20
using just a diode? </DIV>
<DIV>&nbsp;</DIV>
<DIV>Any advice would be appreciated. </DIV>
<DIV>&nbsp;</DIV>
<DIV>thanks!<BR><BR>Seb </DIV>
<DIV>&nbsp;</DIV>-- <BR>You received this message because you are =
subscribed to=20
the Google Groups "BuildBrighton - the Brighton Hacker Space" =
group.<BR>To post=20
to this group, send email to brightonhackerspace@googlegroups.com.<BR>To =

unsubscribe from this group, send email to=20
brightonhackerspace+unsubscribe@googlegroups.com.<BR>For more options, =
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om/groups/opt_out</A>.<BR>&nbsp;<BR>&nbsp;<BR></DIV></DIV></DIV></BODY></=
HTML>

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