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[Solved] LM358 pin2 connect

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g-lock_dk:
hey all

I have a wemos connected to a MCP4725 dac and it works, but the the 5V output from the dac is not enough I need 10V so a asked for help and was told to get a LM358 upamp to boost the output of the dac, but I can´t figure it out how to connect it I use a 12V PSU to the LM358 it will give me 12V output but I just going to make a hard limit in my code in the wemos so it max out at 10V

its for an old light fixture that use a 1-10VDC for dimmer
 
bonus question where do I put the nagative wire from my light fixture on my circuit?

pin 1: +0-10V output
pin 2: ???? what to do about it
pin 3: output from the DAC
pin 4: -12V from PSU
pin 5-7: not connected
pin 8: +12 PSU

magic:
To go from 5V to 10V you need 2x gain, so you feed back 1/2 of output voltage (pin 1) to IN-.
In short, two equal resistors in series from OUT to GND and IN- connected in the middle.
Look up how to set up an opamp in "noninverting" configuration if you want to know how it works.

You may get away with pin 4 at GND and without a -12V supply. The device you are controlling goes between GND and OUT.


But wait, a light fixture dimmer? Mains powered? Are you sure that the 10V control input isn't sitting at some dangerous voltage?

g-lock_dk:
Yes there is a dimmer in my light fixture

I made a circuit diagram

I tried to google noninverting and got nowhere I feel like a caveman in a digital age I need HELP

Kim Christensen:
Here's a caveman edit with some arbitrary resistor values. Not sure what the common is on the dimmer input, but I connected the common from the Op-Amp circuit to what I assume it is. ( Marked with ?? )

Make sure you heed magic's warning that "Dimmer-0-10V" might be connected to mains voltage. It must be isolated from "mains power L1" and "mains power N"...

g-lock_dk:
thanks Kim

gonna try it, after i got some ZZZ its 2.24 here so should be sleeping already but work got in the way :)

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