VDI-RODERICO

[dbanner]

There appears to be some sort of DC offset adjustment (R230) for U206C.

[roderico]

In addition to using a superior opamp, perhaps one could have a play with various band pass topologies to see what is optimum for this this application, in conjunction with the selected opamp. There is online software for this. I'm sure you all know about Filter Wizard. I just only discovered this. https://www.analog.com/designtools/en/filterwizard/

knowing the frequencies where the major contribution of noise comes from (e.g. from field testing) this filter wizard could make it easier to tune the parameters

[roderico]

Here is the topic on the Russian site..... There is also a video test
http://md4u.ru/viewtopic.php?f=80&t=9955

ok thank you, it could be a very good improvement although it will saturate sooner, here it is the frequency response for a 5mV signal with ltspice in case someone wants to tune the values the old is Vout1 and the new Vout2, it would be very good to have a test in the fields where the real noise input is (maybe in the Russian forum says something about the field testing)

[roderico]

I have redone waltr's ltspice circuit with values more similar to the original and it seems to work fine, the phase different is in the amplitude of X and Y (you can take them from the scope view) e.g. x = 2.75*sin(wt) and y = sin(wt), w=2*pi*5 (5Hz) then x/y = 2.75 and atan(2.75) = 70?, at Vout1 you should have something proportional to log(x/y)=0.44, i.e. a constant voltage and this value is then transformed into a different value but also constant (Vout2) I guess the resistors are then adjusted to have a value similar to 70

[dbanner]

Shallow curves. Alright.

[waltr]

Looks like a clown party there, Waltr. Well I can certainly see the compression. The sine waves now have flat tops and rounded corners indeed. So for a changing value of I(R7) and I(R8 ) , there respective outputs V(x) and V(Y) remain fairly constant over some range of input (flat top portion). V(out) is also compressed.
Are the inputs for X and Y in a real working circuit absolute value inputs?

I set a +-10mV sine which is a fairly weak but detectable signal.The picture looks very much the same, just larger Voltages, if inputs are increased.
The Log out signals are not flat top but have a slight curve.

I am leaving the analysis of VDI of output the readers here.

[dbanner]

Modeled a simplified version of the White's Log amp meter drive in LTSpice. The White's circuit has many switches that I did not include.

I injected a 1Hz sine into one log amp and a 1/4Hz sine into the other. This is to 'see' what the log amps do and then what the output of the diff amp (sum) does. The input waveform is show on the plot as the current through the input R's, I(R7) & I(R. This puts the inputs on a different scale (i) to make them easier to see.
First to notice is the Gain compression, at V(x) & V(y), at higher input Voltage, the sine is 'distorted' into a rounded corner square.
Next is the output, V(vout). This would be the meter drive to indicate VDI.

Attached is screen capture and the LTSpice files zipped.

Looks like a clown party there, Waltr. Well I can certainly see the compression. The sine waves now have flat tops and rounded corners indeed. So for a changing value of I(R7) and I(R8 ) , there respective outputs V(x) and V(Y) remain fairly constant over some range of input (flat top portion). V(out) is also compressed.
Are the inputs for X and Y in a real working circuit absolute value inputs?

[dbanner]

Here is the topic on the Russian site..... There is also a video test
http://md4u.ru/viewtopic.php?f=80&t=9955

Thanks, will have a look.

[SWL]

are there somewhere any tests, maybe in the Russian forum?

Can you put the schematic.

Here is the topic on the Russian site..... There is also a video test

http://md4u.ru/viewtopic.php?f=80&t=9955

[waltr]

Modeled a simplified version of the White's Log amp meter drive in LTSpice. The White's circuit has many switches that I did not include.

I injected a 1Hz sine into one log amp and a 1/4Hz sine into the other. This is to 'see' what the log amps do and then what the output of the diff amp (sum) does. The input waveform is show on the plot as the current through the input R's, I(R7) & I(R. This puts the inputs on a different scale (i) to make them easier to see.
First to notice is the Gain compression, at V(x) & V(y), at higher input Voltage, the sine is 'distorted' into a rounded corner square.
Next is the output, V(vout). This would be the meter drive to indicate VDI.

Attached is screen capture and the LTSpice files zipped.

[dbanner]

In addition to using a superior opamp, perhaps one could have a play with various band pass topologies to see what is optimum for this this application, in conjunction with the selected opamp. There is online software for this. I'm sure you all know about Filter Wizard. I just only discovered this. https://www.analog.com/designtools/en/filterwizard/

[dbanner]

[ATTACH]48937[/ATTACH]
What other parts? This is just an additional preamp to basic circuit. It is used to amplify a weak signal X and Y

The other part of the circuit, you know exactly what I meant. It is part of a larger circuit, is it not? So it is part of a micro circuit for VDI. Nice.
Can you put the schematic.

[roderico]

[ATTACH]48937[/ATTACH]
This is just an additional preamp to basic circuit. It is used to amplify a weak signal X and Y

are there somewhere any tests, maybe in the Russian forum? adjusting the band filter to a specific frequency (and thus rejecting the rest) the second stage amp would only amplify the signal (and less noise), but instead of the TL072 I would use a rail-to-rail amp e.g. MCP602 or MCP604 (4 amplifiers)

[waltr]

Perhaps processing a log amp output allows some saving of resources or a lower bit count. I don't know.

Simply, a log amp has more gain with a smaller signal then the gain decreases as the signal gets bigger.
On the Whites VDI meter this allows a reasonable meter indication even with a weak target signal.

When you see a diode across the feed-back on amp-ops, this is a simple log amp that decreases the op-amp's gain with larger input signals.

I am working on the LTSpice simulation.

[SWL]

Are there any more parts of the circuit?

What other parts? This is just an additional preamp to basic circuit. It is used to amplify a weak signal X and Y