Below is a link to my first shot at the Rio Rand Motor Speed

General CNC CNC Routers
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#OXSpindleDriver

Below is a link to my first shot at the Rio Rand Motor Speed Controller schematic.

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Nice job.
Would you agree now that the PWM control in (from tinyG) to Motor drive is DC coupled, not AC coupled as you originally thought?

I have seen on some external motor driver spec sheets that have opto isolator input like this that R65(620 ohms) should be increased if input logic was higher than 5V swing, with a suggested limit of 10ma to the input LED.
In this case, I would guess that logic 1 current flow into the opto isolator from tinyG is 3ma or less, assuming tinyG can source even that much. The 555 timer acts as an amplifier and clipper for the signal at R63, so a direct connect from 3V logic(tinyG, DUE) to the controller might work, but might also contribute to some Duty Factor (I learn fast) reduction at the motor due to rise and fall times on the input pulse.
I continue to prefer a buffer/level translator, such as I show here:

Just FYI - I recently started to use KiCAD for drawings like this.
It is a full Open Source CAD, so far I am just into schematics.
I use on Linux, very fast learning curve if you have done this before.

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@cmcgrath5035 the output of the 555 is AC coupled to the driver Mosfet through a high pass filter and that was my suspect for the reason I can’t get to 100% DF. At 100% the PWM is a DC value.
I did not do any freq analysis on that filter yet. So it’s AC coupled internally.
I ran the numbers configured as a direct input from the tinyg to the coupler LED and it looks like it loads at about 4ma which keeps the output of the coupler in a reasonable range. The specs on the Atmega 192A3 is 20ma, so loading should be ok.
My guess is that the opto-coupler and 555 rise and fall times are a pretty small portion of the PWM signals period especially at 1500hz.
At this point all these theories can be verified by a scope, now that we have a schematic :). I return from vacation in a week and will anxiously complete an end to end test.
I prefer buffers as well to isolate the processors I/O and drive long wires with better noise immunity.

Thanks I will take a look at KiCad. I use SchemIT when I want to share with others as there are no installs and you can imbed the schem into a blog or website.

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@donkjr just wanted to mention bud, I can get 100% duty cycle from the set-up. My current 400w spindle will reach 12150.

Hope you have a great vacation! Looking forward to you getting back already… :slight_smile: