# Mux to DC volts

Discussion in 'General Electronics Chat' started by DexterMccoy, Mar 17, 2014.

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1. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
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U37 is a 741 op amp

U34 is a Multiplexer 4053

Pin#14 has an AC voltage

U37 output is in DC volts

1.) How does the U34 the multiplier convert an AC voltage into a DC voltage or does U37 convert the AC voltage into a DC voltage?

2.) R203 is a 88.7 k ohms , the AC voltage is in AC millivolts , the resistor has drifted to 88.3K ohms

88.7K ohms to 88.3K ohms is a big change when dealing with millivolts, why is that? how much of a change is it? because it's in millivolts

3.) How do you check the continuity from U34 pin#14 and Pin#13 and the continuity from U34 pin#14 and Pin#12?

When the power is On? i need to measure the resistance from these pins

4.) How are they using U34 multiplexer chip? it's used as a solid state relay

2. ### paulktreg AAC Fanatic!

Jun 2, 2008
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A schematic would help?

3. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
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Here are they schematics

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4. ### ScottWang Moderator

Aug 23, 2012
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741 was used as a inverting adder, the AC voltage came from U34 just one of the four inputs voltages.

How did you measured it, and when the power on or off?

You just using the multimeter voltage range to measure the voltage of those pins.

The SSR almost used in the higher voltage as 110V/220V, but here just a low voltage that maybe lower than 30V, when you using CD4053 to switching the AC voltage then the power for CD4053 should be providing as +V,0V,-V, and the input AC voltage better not to over the range of the power of CD4053.

5. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
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How it the 741 an Adder?

I measure the resistance of the resistor out of circuit , i took the resistor out of the circuit and measured it, it measured 88.3K ohms

The AC voltage that is supplies to the 88.7K resistor is in AC millivolts

My Question is when you have an millivolts with a 88.3K resistor VS millivolts with a 88.7K resistor, how much of a change is it? it's a big change from 88.3K to 88.7K because it's in millivolts

But how do you know the millivoltage "Range" of the change? from 88.3K VS 88.7K resistor?

6. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2

NO, I need to know the Resistance continuity , look at the schematic it's a Switch inside the 4053

I need to know how to measure the continuity resistance from the Input pin to the output pins while the circuit is powered On

But you can't measure resistance or continuity when there is voltage applied to the nodes or pins , it will damage my DVM meter

7. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
The designer is using the CD4053 as a Switch or relay , not as a multiplexer

What is this called how they are using the CD4053?

8. ### ScottWang Moderator

Aug 23, 2012
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The circuits of op amp inverting adder.

The calculation infos of op amp inverting adder.

You have to understand the first that how an op amp as an inverting adder.

You can measure the CD4053 independently take away from the other parts only adding the power, and measuring the in/out using the multimeter on R range, that is the pure resistance of I/O of CD4053.

You can't measure as what you said, but you can measure the voltage of input and output and their current, and then through the Ohm's law that you will get the resistance of I/O of CD4053.

Only one situation that you can measure the resistance of I/O of CD4053 directly from the circuit when the power is on, that is when which In/out is ON.

I knew that the designer was used CD4053 as a switch or realy, but the function is still as a multiplexer, does that has any problem?

Last edited: Mar 18, 2014
9. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
How is it function still as a multiplexer? it the output of the CD4053 a modulated signal? how does it convert an AC voltage into a DC voltage?

But the CD4053 have voltage on the I/O, this will damage my DVM meter or get an incorrect measurement in Resistance mode on my DVM meter because there is voltage being measured in resistance mode

Yes I see the Inverting adder

But I don't understand how the circuit converts an AC input from the input of the CD4053 that goes to the inverting adder 741 and gets converted to a DC output

How does this circuit convert an AC input voltage into a DC output voltage?

10. ### ScottWang Moderator

Aug 23, 2012
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A SPDT switch also is multiplexer, but it only working by manual, that's why we need a parts can be working automatically or can be controlled by an electronics signal as CD4051, CD4053, CD066.

The CD4053 can't convert a AC to a DC, it just only a switch, if you want to see how to converting AC to DC, please see the explanation on the last description.

When the I/O control is on, between the I/O only has a little voltage, normally it won't damage the DVM, because the I/O on CD4053 is a AC signal, it maybe got a incorrect resistance values, so that's what I said you can using another method, it can be measure with a pure resistance.

You can see the below link on page 8 - Figure 9. Low-Pass Filter, the capacitor will convert ing the AC signal to a DC voltage as a filter after rectifier, the capacitor will reponse for the related frequency.
Understanding Basic Analog - Ideal Op Amps.

And to see the below link on page 11,12.
Fig. 3.13. Lossless inverting Integrator
Fig. 3.14. First order lowpass filter
The operational Amplifier and applications.

An adder also can be a modulator, it depends on what kinds of signals input and want to be mixed together.

11. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
But there is no rectifier in this circuit, so how is it converting AC voltage to a DC voltage?

12. ### ScottWang Moderator

Aug 23, 2012
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1,029
I'm not sure why you always say that, the inverting adder was mixed four signals to became one signal, added a capacitor only can make the wave more smoothly, but it isn't a rectifier, and the rightest side shows that 98 pitch servo sum on the mux pic#1, so where did you get the idea of AC to DC?

13. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
Elev Servo Pos 95 input is an AC voltage to the R203 resistor
U37 pin#6 is a DC voltage output
It converts the Elev servo pos AC voltage into a DC voltage from U37 pin#6 but how does it convert AC voltage to DC voltage?

14. ### ScottWang Moderator

Aug 23, 2012
6,681
1,029
Could you show me the voltage and waveform & frequency:
1. the middle point of R263,R264.
2. the middle point of R266,R267.
3. the middle point of R269,R270.
4. The ELEV SERVO 95.
5. Pin 13 of CD4053.
6. Pin 6 of U37, Voltage = ? V

15. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
1. the middle point of R263,R264 = ZERO , .017 VAC
2. the middle point of R266,R267 = ZERO , .017 VAC
3. the middle point of R269,R270 = ZERO DC, .017 VAC
4. The ELEV SERVO 95 = .060 VAC not DC volt
5. Pin 13 of CD4053. = .017 VAC not DC volts
6. U37 Pin 6 is .030 VDC not VAC

16. ### ScottWang Moderator

Aug 23, 2012
6,681
1,029
I can't see the waveform, but look the values of voltage and check the circuit, they seem look like the noise not the signal.

If they are all noise then the Pin 6 of U37 is possible to be a Vdc, because the capacitor is a filter, filtering the noise and keep it to a Vdc.

What is the function of this device?

I can't see the whole picture of the device, so i only can guessing.

Can you show me all the circuit and all input voltage of the device.

17. ### shortbus AAC Fanatic!

Sep 30, 2009
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He is repairing/trouble shooting control circuits for commercial airplanes.

Maybe he even works for Malaysia Airlines?

18. ### ScottWang Moderator

Aug 23, 2012
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Haha
commercial airplanes?
Malaysia Airlines?
How did you know that, but I can't figure out, maybe you have a good pair of eyes, or a smart brain ...

Actually I don't care any commercial problem, I just care about the whole picture of the device, sometimes we really need that.

19. ### shortbus AAC Fanatic!

Sep 30, 2009
6,551
3,849
He/they said it over at ETO before they were banned. Look at the schematics he posts, words like flap, elevator, etc, are on them.

Don't know about Malaysia airline, that was a joke.

20. ### ScottWang Moderator

Aug 23, 2012
6,681
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So you really have a good eyes and look at the details, you means that the Malaysia Airlines event just like the David Copperfield's magics?