Looking for a simple as it gets D/A and tried this one

shows OK with LTspice, but actual build ramps right up to the power level(20vdc). ???

 

Looking for a simple as it gets D/A and tried this one

shows OK with LTspice, but actual build ramps right up to the power level(20vdc). ???

What shows OK with LTspice?

 

The opamp’s gain should be 1+R1/R2

 

What shows OK with LTspice?

Circuit as shown in Youtube.

 

My build the output goes up to B+ ?

 

Circuit as shown in Youtube.

Oh..you mean the opamp circuit not the Arduino.

 

My build the output goes up to B+ ?

To get 0-10vdc at output, the supply needs to be 12vdc min.

 

How come the Video and LTspice shows ok for 12-25vdc OK ?

 

My build the output goes up to B+ ?

What voltage is B+?

 

Very simple, measure the DC voltage at the opamp’s pin 3, the noninverting input.

 

How come the Video and LTspice shows ok for 12-25vdc OK ?

So, the gain is equal to 2. If you put 1v in, you get 2v out. So it should work a long as the resulting OUTPUT is 2v less than the supply voltage. I haven't seen your simulation so I don't really know what your seeing.

 

I get the same LTspice results as video in post #1 . but the actual build does not control, it goes up to the 20v sypply?

 

I get the same LTspice results as video in post #1 . but the actual build does not control, it goes up to the 20v sypply?

Are you using single supply?
Is there a load attached?

 

I get the same LTspice results as video in post #1 . but the actual build does not control, it goes up to the 20v sypply?

R1 is wrong value, defective or not connected... or OpAmp GND is not connected... or OpAmp is defective.

if you short R1, OpAmp circuit becomes voltage follower and output will be the same voltage as input voltage at pin 3.

so, you can just measure voltage at pin 3... as long as it is not near supply rails, that is our target.
then measure output (use DMM probe to short pins 1 and 2 while taking measurement).

without shorting pins 1 and 2: voltage at pin2 should settle to match the voltage at pin3, and voltage at output pin1 should be double.

if this is assembled on a solderless breadboard, try moving parts to different part of board to avoid possible board issues.
if it is soldered, power it off and check if there are shorts... sometimes ball of solder rolls under IC or there is a solder bridge invisible to naked eye.
had one not long ago, tiny wisker much thinner than a hair, DMM clearly showed short and i could barely see it under microscope. using tip of a tiny screwdriver, i broke it and - everything went back to normal. in hindsight, i should have kept it to tease colleagues.

 

Use an op-amp that has the same non-inverting input current as the one in the simulator. Better yet, use the other opamp in the package as the driver for the circuit shown.
While it can be called "a D/A converter, I would rather call it a pulse quantity to analog voltage converter.
To serve as a D/A converterIt MUST have a low impedance for both high and low driver voltage pulse input. OTherwise the output behaves exactly as complained about.

 

It should work with any op-amp, it's just a second order filter to remove the PWM frequency. I have used it with an MCP6072.

If you connect the negative end of C2 to the output of the op-amp instead of ground, it becomes a Sallen & Key filter, but don't do that as the op-amp's phase shift causes the attenuation to reduce at higher frequency. You can also make a similar D-A using an MFB filter which has better HF attenuation than a S&K, but it inverts the output.

 

It should work with any op-amp, it's just a second order filter to remove the PWM frequency. I have used it with an MCP6072.

If you connect the negative end of C2 to the output of the op-amp instead of ground, it becomes a Sallen & Key filter, but don't do that as the op-amp's phase shift causes the attenuation to reduce at higher frequency. You can also make a similar D-A using an MFB filter which has better HF attenuation than a S&K, but it inverts the output.

There are SOME op-amps that require a DC return path for both inputs. At least at one time that was the case. For those devices, operation without a DC return was not defined.

 

There are SOME op-amps that require a DC return path for both inputs. At least at one time that was the case. For those devices, operation without a DC return was not defined.

But there is a DC return path. The ATMEGA processor in an Arduino has push-pull outputs, like a standard CMOS gate.

 

1. The video dude forgot the 8th component, a power supply decoupling capacitor for the opamp.

2. That is not a very sophisticated filter. For the same number of components and better performance, connect C2 to the opamp output and recalculate.

ak

 

1. The video dude forgot the 8th component, a power supply decoupling capacitor for the opamp.

2. That is not a very sophisticated filter. For the same number of components and better performance, connect C2 to the opamp output and recalculate.

ak

. . .as mentioned in Post #16. . .
But it is a better filter for the job than a Sallen &Key, because the phase shift of the op-amp causes the output to rise at high frequency. The simple RCRC doesn’t suffer from that problem, but only has a Q of 0.33.
Multiplying the second R by 10, and dividing the second C by 10 increases the Q to 0.5, which is critically damped, the same as a Sallen & Key with two equal C’s and two equal R’s.