RESET circuit tweaks

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exxos
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Re: RESET circuit tweaks

Post by exxos » Sun Nov 11, 2018 11:21 am

because its a extra part.. assuming I sold kits, its another part I have to bag 20 times, another part I have to stock and look for, its another part which has to be soldered.. if I ever went into a production batch of these boards, saving 1 part makes a huge difference.

But really, the 555 isn't really doing anything. So removing it is good thing. Not only that, I want to do away with a lot of inverters on the MB, I can't do that and use the 555 as it needs a inverter on it. One reason the TL chip is good, as it has inverted and non-inverted output.. but it doesn't work, and I don't think we need a chip anyway.

if we stuck with the 555, the next board would still have to have a inverter, which is a extra part, which has to be stocked etc etc.. so basically 2 parts taking up room and cost which basically do nothing.

Also its extra routing on the PCB, less chips makes a good thing as I really had issues routing the alpha in 2 layers..
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Re: RESET circuit tweaks

Post by PhilC » Sun Nov 11, 2018 11:25 am

Ok, now I understand, the aim is also to get rid of the inverter, hadn't thought of that. In turn will free up space.

Good point well made.
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Re: RESET circuit tweaks

Post by Icky » Sun Nov 11, 2018 11:26 am

exxos wrote:
Sun Nov 11, 2018 11:04 am
: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..
Yep - looks like reset line needs to be inverted. I think there is a spare one on one of the chips on the board I can use.

Holding down the reset button and the board boots.

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Re: RESET circuit tweaks

Post by exxos » Sun Nov 11, 2018 11:41 am

Icky wrote:
Sun Nov 11, 2018 11:26 am
Holding down the reset button and the board boots.
You actually need at this point to replace the inverter with a buffer next then. So you need a 74LS07 (open collector buffer) which will remove that inversion, then all should be fine..
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Re: RESET circuit tweaks

Post by Icky » Sun Nov 11, 2018 11:45 am

exxos wrote:
Sun Nov 11, 2018 11:41 am
Icky wrote:
Sun Nov 11, 2018 11:26 am
Holding down the reset button and the board boots.
You actually need at this point to replace the inverter with a buffer next then. So you need a 74LS07 (open collector buffer) which will remove that inversion, then all should be fine..
So you are saying to replace the U1 LS05 with a LS07?

Looking in my LS stash for an LS07.

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Re: RESET circuit tweaks

Post by exxos » Sun Nov 11, 2018 11:53 am

Icky wrote:
Sun Nov 11, 2018 11:45 am
Looking in my LS stash for an LS07.
yep..

ah nope, it wont work , well it will, but midi ports wont work as 2 of the gates in that chip are used for midi... if midi isn't being used, then you can swap out the LS05 for a LS07.
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Re: RESET circuit tweaks

Post by exxos » Sun Nov 11, 2018 11:55 am

You can wire the RC circuit upside down which should do the inversion..

power-on-reset-passive-circuit.png
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Re: RESET circuit tweaks

Post by Icky » Sun Nov 11, 2018 11:57 am

exxos wrote:
Sun Nov 11, 2018 11:55 am
You can wire the RC circuit upside down which should do the inversion
Yeah - I noticed the MIDI hence the ask.

Decision made anyway as I don't have an LS07 everything but. Going for the upside down version.

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Re: RESET circuit tweaks

Post by exxos » Sun Nov 11, 2018 12:02 pm

Icky wrote:
Sun Nov 11, 2018 11:57 am
Decision made anyway as I don't have an LS07 everything but. Going for the upside down version.
:thumbup:

Those other inverters in the midi line will be replaced with buffers (non-inverting) so it won't be a problem on the next revision anyway. Its more just making sure the machine is happy without the 555 in place.
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Re: RESET circuit tweaks

Post by Icky » Sun Nov 11, 2018 12:28 pm

exxos wrote:
Sun Nov 11, 2018 12:02 pm
Icky wrote:
Sun Nov 11, 2018 11:57 am
Decision made anyway as I don't have an LS07 everything but. Going for the upside down version.
:thumbup:

Those other inverters in the midi line will be replaced with buffers (non-inverting) so it won't be a problem on the next revision anyway. Its more just making sure the machine is happy without the 555 in place.
I hope you are keeping track of all these changes and nuances

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