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Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 12:15 am
by Icky
Yep I have both of those.

Just looking at the Rt now

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 12:22 am
by exxos
Seems like that chip is simply junk then to me. Just doesn't do what its supposed to. Could probably design a simple reset circuit using a few,cap, transistor. Will look into it in the morning...

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 12:27 am
by Icky
exxos wrote:
Sun Nov 11, 2018 12:22 am
Seems like that chip is simply junk then to me. Just doesn't do what its supposed to. Could probably design a simple reset circuit using a few,cap, transistor. Will look into it in the morning...
Works fine at 5.4V but below its unusable.

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 12:29 am
by exxos
1-Figure1-1.png
1-Figure1-1.png (6.5 KiB) Viewed 1049 times

Should only really need that above...

Capacitor assumed zero on power up, so charges via the resistor, when the voltage hits about 2v it triggers the gate..

On power down, the 5v rail collapses and the cap is discharged via the diode.

Reset switch goes across the cap.

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 12:33 am
by Icky
exxos wrote:
Sun Nov 11, 2018 12:29 am
1-Figure1-1.png


Should only really need that above...

Capacitor assumed zero on power up, so charges via the resistor, when the voltage hits about 2v it triggers the gate..

On power down, the 5v rail collapses and the cap is discharged via the diode.

Reset switch goes across the cap.
Sounds right. For something so simple there are many designs and chips out there. Even Atari have used different circuits in each of their machines.

I thought you were going to look at it in the morning ;-)

I have my morning planned - SR98 Recap

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 12:42 am
by exxos
Yeah but I thought there be a image on Google and there was ;)

I don't see the need for a ic to do this job. The only missing feature is if the voltage drops below 5v it should do a reset, but who cares ? I mean if powers dropping the machine is going to be not functioning regardless if reset is triggered or not.

So take out the reset board and try the simple circuit instead ;)

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 10:59 am
by Icky
exxos wrote:
Sun Nov 11, 2018 12:42 am
Yeah but I thought there be a image on Google and there was ;)

I don't see the need for a ic to do this job. The only missing feature is if the voltage drops below 5v it should do a reset, but who cares ? I mean if powers dropping the machine is going to be not functioning regardless if reset is triggered or not.

So take out the reset board and try the simple circuit instead ;)
A good mantra to have "keep it simple" have been doing that for many many years.

Reset board has now been removed and now looking at a simple solution based on your thoughts last night.

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 11:04 am
by exxos
:thumbup:

If we can do away with the IC 555 or whatever,then its saving pcb space and the cost of a part. We got the cap and resistor and diode already on the MB... May need to swap around if we need to invert the reset line... But pretty much just remove the 555 and link over the rc line to the 555 output..

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 11:05 am
by PhilC
Morning,

Can't help think why don't we just keep the 555? I know you want to limit the amount of chips etc but if the reset chip fails it's easier to diagnose a faulty 555 than start looking at failed components?

Re: RESET circuit tweaks

Posted: Sun Nov 11, 2018 11:06 am
by PhilC
That and 555 cost pennies.