And, "disaster"? Isn't that rather dramatic?
260k for the "avoiding long term battery drain in a NON-PWM application" case.
And, didn't I explain how I chose 260k?
R1 = (Voutput - VBE)/IB = (3.3V-0.7V)/10µA = 260k
R1 = (Voutput - VBE) * 10/IC = (3.3V-0.7V)*10/1mA = 26k
I think you mean IB here, NOT ICand 260k NOT 26kLike this:R1 = (VIN-VBE)/IB =(3.3V-0.7)/10uA = 260k
As stated, NOOBs are hammered with connecting the Arduino GND to the external power supply GND.Your circuit's ProMini is being powered via +V power supply.You are connecting the ProMini Vcc (3.3v) to the external load battery supply +3.3v for the circuit return path.No effort was made to warn the OP to not connect Arduino GND and external power supply GND.We can all offer weird and wonderful ways of biasing and referencing circuits.However, we should have the foresight to tell new people what might happen if GNDs are then connected.
"Ground" is an arbitrary concept
But, why would anybody do that -- noobs included?
Whence did I use "hfe"? Or, more to the point -- if you saw hfe, then apologies. Must have been a typo, since I fully meant "HFE"
Back in the day, Ground actually meant, It's connected to the Earth.
Never said or implied you wrote hfe.This was to show the OP where to get the data from hence the FYI.
Sorry. It was presented in the same context as you scolding me about not save NOOBs from themselves. Thus, I assumed it was further scolding
So why is it connected to the regulator output ?
There is no scolding here.
The point was new people here often have difficulties reproducing simple schematics to actual circuits.Any kind of multiple power supply situations quite often gets NOOBs confused and into problems.
When they do run into problems, they are often asked to take test measurements and confirm GNDs are connected.
As mentioned by you, there are things called "Rule of thumb . . . .", rules of thumb are great.Well, it is 'my opinion' (yes 'my' opinion) and Rule of thumb, that for interconnected power supplies, use 0V, GND, negative as a return path.
Yes you can connect the positive of a battery to the 0 volt pin of another power supply. Yes you can connect the positive of a battery to the positive of another power source.Doing so is not wrong but following my rule of thumb keeps new people on a even footing where they hopefully don't experience problems.
yes you can connect the positive of a battery to the positive of another power source
>> 3.3+1.5ans = 4.8000