[sdiy] PSU rise-time and uP reset

[Trevor Page]

Hi again,

Many thanks indeed for all of your opinions so far on the reset circuit
issue. Yes, it would be wise to go with the external reset circuit if it
could save some problems in the future, as I know it will be operated
using various kinds of supplies - presenting a whole bunch of unknowns -
and no doubt the occasional iffy PSU too. So I shall shove a safe reset
circuit in there and be done with it. 

While I'm rattling away an email to the list, I have another completely
unrelated, and OT question: has anyone here (maybe you, Magnus?) had any
dealings with implementation of GPIB interfaces at all?

Trev 


> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl 
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of 
> Magnus Danielson
> Sent: 14 July 2003 23:51
> To: t at introspectiv.eclipse.co.uk
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] PSU rise-time and uP reset
> 
> 
> From: "Trevor Page" <t at introspectiv.eclipse.co.uk>
> Subject: [sdiy] PSU rise-time and uP reset
> Date: Mon, 14 Jul 2003 22:01:22 +0100
> 
> > Hi list,
> 
> Hi Trevor,
> 
> > This is going to be a bit of a 'How long is a piece of string' type
> > question, but here goes.
> > 
> > Say we have a microcontroller that contains an internal POR 
> (Power-on
> > Reset) circuit. The datasheet for this device specifies 
> that the +Vdd
> > rise rate, to ensure good POR operation, should be at 
> minimum 0.05 V/ms.
> > If this cannot be guaranteed, then the user is advised to use an
> > external reset circuit. 
> > 
> > I know a reset circuit is only a negligable amount of 
> components, yet I
> > am still curious as to whether I could get away with using 
> the internal
> > reset circuit or not. The design in question is a MIDI to 
> CV converter
> > (yawn!) that will be used by more people than myself and I 
> have no idea
> > what sort of power supplies are going to be in use. 
> > 
> > Would it be unsafe to make the assumption that the rise 
> time of the 5V
> > from my on-board 5V regulator, which takes its power from 
> the modular
> > +12/+15V PSU, is going to take longer than, say, 100ms to 
> fully rise?
> > 
> > This is a really stupid question, isn't it? I reckon I 
> should just stick
> > to using a slow RC reset.. 
> 
> If I where you I _would_ stick with the RC-network stuff. 
> Why? Not that it is
> the neatest solution, but it is a way for you to avoid 
> getting a bunch of
> questions from customers using the brand X PSUs and not the 
> flashy brand Y PSU
> which you used for all the testing. That is, you don't have 
> control over how
> fast the rampup really is, so why not make yourself 
> sufficiently independent of
> it to make this issue virtually irrelevant in your relations 
> to all those other
> people having it.
> 
> But I agree, it would be neat to do without it. Minimalism is 
> an artform in its
> own right, but you should cut the right corners. If you where 
> suppling the PSU
> to go along with the MIDI-2-CV then you could rely on it's 
> rise-time to make
> it work. But that would be more hassle for you I guess...
> 
> Cheers,
> Magnus - DIYed a new gate for the summerhouse today - a 
> hammer & nail job!
> 
>