[SOLVED] How to reduce op amp clamp Vout to 0V?

[d123]

Hi again,

One other thing, eye is logarithmic in response, maybe in coding consider doing this -

PWM Exponential LED Fading on Arduino (or other platforms)

For a project I am working on I needed to dim a LED strip light using the PWM (pulse width modulated) outputs on an Arduino. The most straightforward way to do this would have been to linearly vary the output frequency. Shown below in an Arduino sketch: // Use pin 9 as the PWM output const int...

diarmuid.ie

Regards, Dana.

I read the article, it was enlightening. I'll add this, on the same subject of linear and logarithmic dimming:

How to dim a LED for Human Perception

At first thought, I suppose that one analog solution (at least for my circuit) might be a simple resistor to V+ before the pushbutton for 'slow on', and a resistor to ground behind the 'slow off' pushbutton, both pushbuttons meeting at the charge capacitor, followed by an inverting amplifier into the capacitor to make the capacitor charge and discharge curves look like the desired curves in the articles. Fast on and fast off might not be so simple, depending on current.

Anyway, interesting articles.

 

[danadakk]

Hi Dana,

Thanks. Yes, I remembered human perception is not a good measurement tool, to phrase it that way. And, the DMM shows a steady rise and fall when I press the slow charge and discharge buttons but it feels rather different to my eyes. I'll read what you've linked to during/after dinner.

--- Updated Oct 11, 2020 ---

I'll add this as an update as it's unrelated to your post.

Get the (pardon my English, but it's the only honest adjective) s**tfest of a shutdown circuit I came up with - it actually works unglitchily, unbelievably. It draws >900uA , maybe the ~300uA of the LM4041 isn't so bad after all...

Useless for this circuit, but fun to think through and put together, at least. Would be useful if Iq were e.g. 5mA or 10mA.

Haven't drawn complete schematic, just a functional block schematic. Have a good laugh at it, I am.

View attachment 164698

Congrats, I used to do a lot of analog design, now not so much anymore because
so many sensors now come with the signal conditioning onboard. Nice work.


Regards, Dana.

 

[d123]

Hi,

As this thread has gone on for ages, and members have been very helpful with the circuit, I'd like to close it with the 99% finalised schematic of a working version on a breadboard, and just say thanks.

This is the breadboard (the two AND gates are actually made from four BSS188s someone was nice enough to give me, so thanks very much) ...messy spaghetti wires... (SOT-223 transistor bottom right, between 2N2222A and both PDIP ICs is not doing anything and shouldn't be there):

There is an edited 1-minute video showing it working, but I don't seem to hit on edaboard formats - I converted to avi and mpeg but the upload section can't see them...