septillion:
Low indeed makes the pin GND. And it's okay to use that as a GND as long as you mind the current. Aka, if that motor driver only uses that as a reference for the logical inputs it's fine. But it can NOT supply the motor current.
the thinking was indeed to keep it for only the logical side.
this motor driver doesn't "mix" the supplies with the controller, like the L293/L298 motor shields where you can pipe out the 5V for the microcontroller via the motor shield connection.
it's a "L298 replacement" from eBay(China) which i've tracked down as the MX1515.
the datasheet is in chinese and an english version doesn't seem to be available.
FWIW: this is what the schematic looks like;
Datasheet itself is at;
MarkT:
No, this is not good practice - output drivers on the ATmega chip have about 40 ohms of resistance, very roughly,
too high an impedance for anything that takes current and wants a stable rail voltage, which expect a
solid voltage source. Most modules or circuits you might want to power this way have (and need) decoupling capacitors,
so switching them will involve current spikes well in excess of the output pin's 40mA aboslute maximum.
oh my, i understand the individual words in those sentences, but my grounding in fundamental electronics is weak and can't quite piece it all together.
i was thinking "high impedance" was in MegaOhms, but that was dealing with Arduino input pins.
so, i can't quite get reading 40 Ohm as "high impedance".
MarkT:
However if you are proposing commoning up several pins (and using direct port manipulation to switch
them simultaneously) you will be mitigating both problems...
okay - so it looks like it's time i started learning direct port manipulation.
i see that D4-D7 (and D3) are on the same port (D) - can i use Port D then ?
does this mean i will have to "sacrifice" using the other pins on Port D - D0-D2 inclusive ?
(or handle/cater to them also in the code for the direct port manipulation, i believe one uses bitmasking to leave "other bits as is")
this looks to be a good learning lesson opportunity.