RESET circuit tweaks

[exxos]

I hope you are keeping track of all these changes and nuances

Not really the thread here is where I got up to...viewtopic.php?f=19&t=1230

I have been working on the STE boosters all this past week, plus now I have the PSU's to test and box up for my store.. plus I got distracted with my 3D printer, so not had time to make any more changes to the schematic lately

I need a good run of free time to sit down and look at all the gates to remove and change etc.. I may do some little LS replacement boards to test these changes.. but again.. time is not on my side at the moment

Once I get this stuff out of the way, I hope I can start making more changes to the thing.. though mainly its spending the video dac board more than anything.

[Icky]

Right - tried the inverse diode, resistor, cap & switch combo using my makeshift reset circuit hack

Initially I used 10uF and 10K as per the original circuit but that was a no go. Turn on and reset press did nothing as it just sat at white screen.

Reduced the resistor to 1K and on switch on nothing white screen but on reset press it resets (boots) so we are missing the initial reset on power on.

IMG_3259.png (863.85 KiB) Viewed 1300 times

[exxos]

so we are missing the initial reset on power on.

Check the voltage on the cap, it should drop to 0v (or close to) on power down, it should "track" the 5V rail dropping.

[Icky]

so we are missing the initial reset on power on.

Check the voltage on the cap, it should drop to 0v (or close to) on power down, it should "track" the 5V rail dropping.

Yes the voltage on the cap drops to 0v on power down. Was wondering if we needed a different cap value and tried a 22uF the power down tracking of the 5V rail was better but still no reset on boot.

[exxos]

Odd.. The cap at 0v on power up means reset is pulled high.. Then as the cap charges, reset starts going low.

Something like 10k and 47uf. Should work... I guess it may need 22k even. Higher values will struggle to charge the cap up.

[Icky]

Seem to of got it working with 1.5K and 47uF. Been playing around with different values.

This seems to be the best so far but there is still an oddity sometimes when hitting the reset button quickly the screen jumps stays on the desktop but its frozen and the res got bigger i.e. the borders got smaller.

It you hold the reset button down for about a second in this state it resets

[Icky]

Cleaned up old reset circuit ready for new one. Reset switch swapped to be +5V.

IMG_3260.png (503.55 KiB) Viewed 1278 times

[exxos]

This seems to be the best so far but there is still an oddity sometimes when hitting the reset button quickly the screen jumps stays on the desktop but its frozen and the res got bigger i.e. the borders got smaller.

Might be iffy contacts on the switch maybe ?

[Icky]

This seems to be the best so far but there is still an oddity sometimes when hitting the reset button quickly the screen jumps stays on the desktop but its frozen and the res got bigger i.e. the borders got smaller.

Might be iffy contacts on the switch maybe ?

My thoughts too that’s why I am cleaning up the board to use the proper switch etc

[exxos]

My thoughts too that’s why I am cleaning up the board to use the proper switch etc

I guess thats the problem with switches, it would be better if it driven a "one shot" timer like the 555..