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Nick
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| simple resistor led question |
 Posted: Fri Oct 22, 2004 12:32 pm |
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I have my pic pin turn on an 1ma LED and a SSR off the same pin, should i put the resistor before the i split the line off to the two different compents? I want to limit the current to each of the compents? My other idea is to just put the resister between the ground of the led and ground of the SSR
btw when I say SSR i mean solid state relay.
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newguy
Joined: 24 Jun 2004
Posts: 1908
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| Posted: Fri Oct 22, 2004 12:50 pm |
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| Your SSR might not like getting anything less than 5 V (or whatever your Vdd is). Run a line from the SSR directly to the PIC. Put the LED and its resistor in parallel with the SSR. I assume this is an indicator LED so that you know when the SSR is active? |
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yerpa
Joined: 19 Feb 2004
Posts: 58
Location: Wisconsin
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| Posted: Fri Oct 22, 2004 2:35 pm |
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| Better check the specs for your SSR. Using a separate resistor for the LED and another for the SSR would be the safest - to use a single resistor you first need to know the forward voltage drop and recommended current of both the SSR and the LED. Running a line directly from the PIC to the SSR will blow the input of the SSR if it is not internally curent limited. |
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simple resistor led quest
Guest
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| simple resistor led question |
| Posted: Fri Oct 22, 2004 2:49 pm |
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If the spec's read 3~30vdc, the resistor is built in.
Most SSR have built in current limit.
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newguy
Joined: 24 Jun 2004
Posts: 1908
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| Posted: Fri Oct 22, 2004 3:16 pm |
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| Quote: | If the spec's read 3~30vdc, the resistor is built in.
Most SSR have built in current limit.
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Sorry, that's what I was assuming. I just put together a project with a SSR that's driven by 5V, and draws about 40 mA when being driven. I ended up driving through a 2N7000 fet, as that's more current than a PIC pin can source. |
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