Hi @Bryan160034
Thanks for your patients while I experimented with this.
I love this design and you’ll be pleased to know I’ve adopted it into my project.
Kinda did but kinda didn’t.
My original design looked like this, with the adjustment of putting the lamp first.
It had two issues:
Firstly, putting the lamp first was possible but challenging in the context of existing wiring.
Secondly, I wanted to use 2watt resistors so I had plenty of head room. I had calculated 120ma * 12v = ~1.45w. Unsurprisingly it’s hard to source weird low values like 14Ω 2w resistors.
I resorted to combining some combination of 50Ω, 75Ω & 120Ω 0.5w resistors in parallel to distribute the power and chase those low values. That took me down another rabbit hole of how power is distributed over parallel resistors of different values.
So, I suppose I technically did get that working, but it got ended up finicky and ugly.
Here is what I came up with based on @Bryan160034’s design.
These are the resistor values that worked best with my lamp.
It elegant and clever too. Learned a lot building it.
I did wonder about this too.
The AtTiny85 has internal pull-down resistors I could take advantage of.
In the event that PB0, PB1, and PB2 are LOW, then Q2 would be essentially floating.
My instinct Is that I should put some kind of pullup/pulldown resistor on the base of Q2.
I could add a 200k+ pull down resistor, which would parallel to R10, R11, and R12. Not sure I like that solution.
I could add a pull up resistor, which would create a voltage divider.
Transistors are current controlled, not voltage controlled, so maybe that’s fine, but it still “feels” a little weird to me. Then again I see voltage dividers on transistors in circuits all the time in text books.
Is this something to be concerned about or am I worrying about nothing.
