teknora

Hello,
I have a wireless Brother printer in a small network (PC, printer, tp-link router+access point). I can print without any problem. But I can't print to file. I have tried all combinations available ports and connections. How can I create a virtual printer capable of printing to file. I am stuck, I will appreciate your replies and inputs very much.

To Studiot:

Thank you a lot. Right now I am analysing the references.

To Studiot:

Thank you very much for taking time and instructive explanations. I think you are the right person to ask. I want to learn very well the voltage distribution in circuits (either simple or complex). Could you give me a good elementary reference for this purpose.

With reference to my attachment showing comments.

 

A modern voltmeter for this purpose is likely to have an input around 10 megohms.

This is in series with the meter.

I have shown this in my fig1.

 

My fig2 shows how this voltmeter is connected in your circuit 4-39a and identifies the floating voltage pont B at the base of the transistor.

 

If you look at my version you can see that the base is not connected to any voltage but is earthed (connected to zero volts) through the 10M of the voltmeter.

In theory the voltage at the base is indeterminate since it is not connected to anything. (In theory it is totally isolated from the base and emitter by the internal structure of the transistor.

In practice the leads and internal circuitry of the voltmeter form a crude antenna which picks up stray (mostly radio) voltages across its terminals.

You can see this effect on the voltmeter by simply turning it onto a low micro or millivolt range and watching the random readings.

As soon as the voltmeter is connected into a complete circuit this effect will disappear or be swamped by the usual action of the live circuit.

However in the connection shown it is not connected to a complete circuit since the base is not connected to anything, except the transistor base.

One of the voltmeter's terminals is tied to earth, so the random pickup voltage will appear at the other one ie the one connected to the transistor base, thus varying the apparent voltage at the base.

Note this voltage is only likely to be present when the voltmeter is connected since the base leads and circuit board pads are short.

 

My fig3 shows the voltmeter connected to read the open emitter voltage as in your fig 4-39f

 

Here we have a different situation since with the voltmeter connected the transistor has full connectivity, albeit through an excessively large emitter resistor.

This 10M emitter resistor restricts the collector current to slightly under 1 microamp, bu that is enough to almost turn on the transistor as we see that the base is at 3 volts and the emitter at 2.5 volts + , just slight under the normal 0.6 to 0.7 base emitter voltage for a correctly biased 2N3904 in the active region.

 

I have noted that the book explanation says this rather more briefly.

 

voltest1.jpg

To Studiot:

Again, I have a question related to Figure 4-39a. No current through the transistor because the base is open. The collector side of the transistor is 9V, the emitter side of the transistor is 0V. The both sides of the resistor (Rc) are 9V. Both resistor and transistor are electronic components. But here the transistor behaves like an open (all voltage drops across it but no current). What are the physics in the transistor and resistor here. What makes them act so different? You have said that in DC voltages the transistor can be considered as an assembly of resistors. Also, why is there no voltage on the open base tip almost in the middle of the transistor? Think an open in a simple circuit with only a battery and a resistor. In the open still there is an electrical field. Because of this field, the is a voltage in the open. If we put a charge there, it will move because of that voltage. So, why is there no voltage on the open base almost in the middle of the transistor?

Thank you very much Studiot for theoretical and practical explanations together with nice illustrations. I also thank Danijel for treating the question from other aspects.

To Studiot:

Why does the author call “floating point” specifically only the cases of Figs 4-49a and 4-44? As far as I understand, the ground is floating ground ,which isn’t connected to Earth. In this case, aren’t all voltages measured floating, Vcc or Vbb?

In your statement “In theory the voltage at the base is indeterminate since it is not connected to anything. (In theory it is totally isolated from the base and emitter by the internal structure of the transistor.)” Shouldn’t it be “… from the collector and emitter…”?

So, based on this explanation of yours, in the non-conducting state of the transistor, I understand that all the leads can approximately be considered as separated parts not touching each other. Am I right?

I would like to ask a general question: If we consider a transistor as being consisted of internal resistors (internal resistances between collector, base and emitter), would the voltages measured be like those in true resistors? For example, would the measured voltages on points between collector and base be between 9V and 3V?

To Danijel: In your statements:

“We could debate this. It might actually be higher than with the connected voltmeter (but certainly below some 0.5V). In any case it is quite floating and so who cares...”, what do you mean by some 0.5V? Also, what do you mean by “In any case it is quite floating and so who cares...”?

“Regarding the picture 4-44 in the OP, I think the book might be partially in error. Depending on the voltage supplied at the transistor base, the voltage at the collector lead might be higher than few mV. It is actually similar to the 4-39f case.” In this case, the collector lead is also grounded like the emitter lead by multimeter ground. Is this is the reason why more than a few mV?

“…The base-emiter junction voltage rises up slightly so that the system reaches equilibrium…” Could you clear up this for me please?

 

I am attaching 3 figures from a well known book (Electronic Devices by Thomas L. Floyd). How does a multimeter measure µV and mV on Figures 4-39 a and 4-44? How does this part of the transistor behave as a floating voltage point? And also how does it measure 3V on the base side and 2.5V or more on the ground side of the transistor on Fig. 4-39f?

 

I am mistaken. I have corrected the original post.

Floating voltage points.pdf

I am not extremely sure about this one,

http://www.esseshop.it/pasta-termica-revoltec-thermal-grease-diamond-menge-6gr-p-19379.html

 

ps. You need to visit your local computer shops to see what they have...

Thank you my friend. I have checked its specifications. It is computer thermal grease and non-curing. I need the curing one. On the specifications, its matrix material isn't mentioned either.

How about computer thermal grease?

https://en.wikipedia.org/wiki/Thermal_grease

Can be bought in computer shop.

In link there is list of compounds used to make them with properties.

Thank you very much for the answer. From the reference, it seems epoxes and silicones with diamond filler would be the best one. But I don't know a product with such composition. I searched in amazon.com and aliexpress.com but I couldn't find.

I want to fix an electronic component working around 135 degree celcius by a material which must be thermally conductive and electrically insulating glue, adhesive, sealant or filling. Could you help me?