Ah, I've seen that kind of cct for MCLR in several places, and wondered what
was going on.  It now makes more sense, thanks.  I want to put in place a
header for connecting to Wouters Wisp628 (which I have bought, but not yet
used), and use it for ICP.

I am providing all power from a 12vDC plug in adapter (it says it's regulated,
should be ok out of the box, right?), then I'm using a couple of LM317LZ's
(with caps' and resistors) to produce the 5v and 1.5v from this for my
application.  The 12v is solely used to drive the relay (via the transistor).
Is this setup ok, or were you thinking something different?

Regards,
Mark

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu]On Behalf
> Of Jinx
> Sent: 23 November 2004 12:38
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] I/O Pin cct design help please
> 
> 
> > Fortunately, I've been through the relay driving part of the cct a
> > few times with a colleague at work who has a degree in electronic
> > engineering, and he suggested the same changes - i.e. the diode
> > across the relay coil
> 
> It's also required on other coil devices such as solenoids. It diverts
> the back-EMF resulting from the coil's field collapsing when the coil
> is turned off. Without it there's the risk of stuffing the 
> transistor, at
> least
> 
> Even with this diode in place the circuit, especially Mclr, may still
> be susceptible to pulses that reset the PIC, hence also isolating the
> 12V and 5V supplies with diodes and reservoir caps. It's good
> practice to power devices like coils from the unregulated or non-
> PIC supply
> 
> _______________________________________________
> http://www.piclist.com PIC/SX FAQ & list archive
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> 

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