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MP
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I am not sure I followed the concept, so excuse me if I am way off the track here...but wouldn't a CD4066 CMOS switch IC do the job without the additional circuitry?
MP -
You can control the motor directly from the PC. A stepper would be easy but you would need some type of feed back circuit to tell you where you really are. This could be opto switches, etc. The other choice would be a servo motor with the internal feed back which always knows the position. The part from the PC is a simple matter of sending pulses from the PC port to the motor. There is no reason to use a microcontroller or plc if you are using a PC to control this circuit. You should research motor control from a PC.
MP -
This can be done with 555 timer chips. There is a link to a tutorial with examples in another area of this site. There is also a large project area which might have what you need. Have you browsed the site?
MP -
The boost with transistor(s) is how I do it, also. Although I use a NPN instead. Either method can be used. The reason I jumped in was your statement "CANNOT". And as you see, it CAN be done.
You are correct that you will have some loss due to the resistors, but overall, you will have a boost in current handling. If a 12 volt regulator is rated at 1 amp, then this would mean the internal resistance can be resembled as 12 ohms. 12/12 = 1 amp. If you add the 0.22 resistance, then 12/12.22 = 0.98 amps. If you have two regulators in parallel in this manner, you will now have the capability of 1.96 amps, which is not double, but is close. If someone is needing to get exactly 2 amps out of 1 amp regulators, then this will not quite get them there. But if they need to get more than 1 amp or need to push this regulator a little over it's limit, then it is certainly a solution. Especially for a beginner who is not up on transistor formulas and cannot build a device with transistors. All they need is ohms law, a couple of resistors and another regulator.
I am not telling you your method is wrong. Just that the other might be an option for some. ;)
MP -
Thanks, the post ended up out of place and it was not clear to whom you were answering.
I agree that it is not good practice to parallel the power supplies, but you should know that it is general practice to parallel regulators such as the 78XX or 79XX series to get more current rating from them. In this case, it does work. When doing this, you should use a small resistance like 0.1 or 0.22 ohm between the output pins because all regulators are going to be a little different and this will keep the current flowing equally between them. This is the same practice as paralleling power transistors.
MP -
The power supply is capable of 3 amps. I could not access the link to the rheostat, but Radio Shack does not carry a rheostat capable of more than 500 ma if I recall correctly. As you decrease the resistance to ground in your circuit, you are asking the resistor (rheostat in your case) to carry more current. V/R=Amps.
Hope this explanation is helpful.
MP -
You have to be careful on this type of generic voltage calculation as some high powered amps are using DC to DC converters and are actually running on 35 to 45 VDC. This changes the calculation considerably. Although it still runs from a car battery at 14 VDC, the amp is running on 35 or 45 VDC.
MP -
Nettron, I refer you to the data sheet of a 4066 cmos switch. Internally, pins are commonly shorted together by some type of reaction to the other pins. For example, without the data sheet on this chip, one might connect a test circuit which adds voltage to the control pin and causes two other pins to "short" together as "close".
Knowing that such an example is possible makes one cautious to look at the internal workings of a chip when making such a test device. When grounding various pins or adding an excitation voltage to various pins on a chip, there are cases when other pins are affected and can become "shorted" together.
MP -
siddhu, this is interesting. What physical size was your capacitor and what Farad rating did it turn out?
MP -
audioguru, what are you referring to in this post? Multiple regulators in parallel? Complete supplies in parallel? Which post are you replying to?
MP -
He said shorted together. After looking at the diagram he has posted it should be clear that he is using the term "short" to mean connected together. What is not clear is what is connected to what in the IC. When you have a schematic with an IC that performs as some type of switching mechanism, it is good to add the internal working devices in the schematic so that it is more clear to see the function. Many manufacturers like to keep their chips as a mysterious black box so that it is not so easy to duplicate the product. Hopefully, desmond does not have this problem.
MP -
I probably should not have gone on so long winded with that last post. Let's continue the filter design theory in the theory section if you want to continue the discussion there. Lets keep this thread going for the low pass filter Rich needs to get going, ok?
MP -
If I am not mistaken, the term 2 pole or twin T refers to two networks that look like a T built from capacitors and resistors where the bottom of the T is connected to ground. If the two components that make the top of the T are resistors, then you have a low pass filter whereas if the two components that make up the top of the T are capacitors, you have a high pass filter. In this type of circuit, you would cascade as many T's as needed to get the roll-off desired. With an op-amp for each section you do not lose the amplitude.
The high order filter is a little different. The second section should look familiar as a sallen-key high order design. The first stage is a simple first order low pass network which definately has the T network you were referring to. There are a lot of designs for filters, but the most popular that you might find is the Chebyshev and the Butterworth. Many others are one variance or another of these.
MP -
If you can post it here, I am sure you will get many comments and suggestions. When you attach the graphic such as a jpg, it will display it in your post.
MP -
It is a third order lowpass filter. The gain is fixed so I am not surprised that Rich is having a problem with the gain. Although you can add gain to the output, if he is using a passive input such as a microphone, then he is going to need some amplification at the input. Microphones give out a very weak signal. Another option is to use a powered mic.
MP -
Here is a site with the same interest:
http://www.interstice.com/drewes/answer/
MP -
Here I will add a few:
http://www.geocities.com/puo_mcchin/Download.html
http://www.commlinx.com.au/schematics.htm
http://www.datasheetarchive.com/
http://www.designnotes.com/Circuits.htm
http://www.keelynet.com/sources/schema1.htm
http://www.glolab.com/freeinfo/info.html
http://www.epanorama.net/index.php?index=circuit
http://www.web-ee.com/Schematics/schematics.htm
http://users.otenet.gr/~athsam/database.htm
MP -
Here is a comparison of the data sheet specs. These diodes have some differences. Have you checked to make sure all of you components are oriented correctly? I have not built this project, so I do not know the specs on it. I suggest that you check the parameters of the data sheet with the component used. Did you have trouble finding the correct component?
MP
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Hi Rogy, welcome to the group!
Fc is the frequency of cut off for high and low pass, but it is the center frequency when you are using the band pass output.
The following formula applies to this filter:
Fc - 1 / (6.28 * R * C) where Fc is the centeror cut off freq., R is R2 through R9 in ohms and C = C1 = C2 is in farads. So, if you are looking for the relationship to C, you can rewrite the formula as C = 1/ (6.28 * R * Fc). If you have a filter that has already been built, you can plug in the R and C numbers and find the Fc from this formula.
MP -
desmond, it seems that you are certainly going to need to get the data sheet of the chip to see what is in there. Most data sheets will give some kind of an internal diagram. Once you have this, you will be able to find a solution. As you have stated, there are resistances and shorts internal to the chip that is causing you the problems.
MP -
What is supposed to happen when you close the switch? All LEDs light? What actually happens? Does this sit on top of the chip in your second diagram or does it plug into the board where the chip would normally be?
MP -
It is always a good idea to use an optoisolator when connecting a device capable of EMF to a computer.
But sec brings up a good point. Is the 5V source coming from other switching circuitry or is this just part of the power supply?
At the very least, you should include some power diodes across the terminals of the fans so the EMF does not cause a momentary short on your computer power supply. Then you could just use the switch as is. If the 5V and switch is representative of a microcontroller or some other similar circuitry, then you must have the optoisolator or other type of protection.
MP -
So do I understand that you have 26 connections to poll at the same time and you are looking for one of the connections to be shorted? It would help to see the circuit, but here are some ideas:
26 of the same circuit in parallel
Add some rotary switches
Use 4066 cmos switches
Do you have a way to post a drawing of the circuit? I have noticed more people tend to get involved when there is a drawing or schematic attached. you know the old saying, a picture is worth....
MP -
One other thing I thought about that was not mentioned in your post:
Have you checked the data sheet for the 4N25 to see if it is capable of the current required by the fans?
MP
4N25 Schematic check
in Electronic Projects Design/Ideas
Posted
Here is a control circuit (switch) that can be used with most any small PNP transistor such as 2N3906. When the resistor to the base is connected to ground (or close) the transistor is in an "ON" state.
The diagram shows the switch used to turn on a relay but it could be used the same for a motor such as used in a small fan.
MP