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

Backwards. You would normally connect power to the collector. These are NPN transistors. Are you aware the fans have two different voltages? Are they different fans? MP

Because of the high impedance of the circuit, you might consider making a LED probe which only comes on when the circuit is shorted. The shorted contacts would complete the circuit. MP

This area is fine for this question. However, it might have gotten more exposure in the circuit requests area. It is really hard to answer this question without at least a block diagram of how your system is put together. There are so many different types out there that a generic answer would most probably be the wrong one. If you are distributing an NTSC signal over different inputs, you will need to make a video amplifier. If you are just needing to connect audio devices to speakers without going through the TV amplifier, then you will need to build an additional amplifier. MP

Not directly replacable by the MN1024, but you could use it instead if you lay out a different circuit board. It uses a different pin out and clock ckt. The SAD1024 was very prone to circuit noise whereas the MN1024 was not. In fact, the SAD chip was so bad with noise that you would almost always see a compander used in conjunction with it to get rid of the noise. BTW, the MN1024 is also obsolete. The digital delay lines took over, although this was after I quit fooling with these chips so I am not familiar with what is presently the popular delay line. Perhaps someone would like to continue this discussion in the "Circuit Ideas/Requests" area of this forum. MP

The SAD 1024 is a "Bucket Brigade" analog delay chip made by Reticon, discontinued several years ago. It is obsolete and you will not find one except in some rare surplus lots. If you happen to have one, you will find that they were used primarily for flangers, chorus, and echo music effects. I do not think I have an electronic copy of the data sheet but I am sure I have a hard copy somewhere. I will look around for the hard copy and see what it will take to turn it into an electronic copy if no one else posts one to this forum for you. What do you mean by "you need an application" for the chip? MP

You might want to start here: http://pasture.ecn.purdue.edu/~abe591s/Opamp.pdf MP

Here is the Parallel Port. ;) MP

AnaChip AP34063 Bay Linear B34063 ADD Micro AMC34063 It looks like a lot of companies make it. Just try different manufacturer letters and keep the numbers. Hope it helps. MP

I access the site from a few different computers. One of these does use 600X800 and it is a little more work, but this does not bother me that much. I just move the pane so that I see the post and not the icons on the left. I have more problems with the pages loading slow. I have a pretty fast computer with a DSL connection, so I am not sure if I have a setting wrong on my computer or if everyone else experiences this also. MP

Yes. I/O refers to "Input"/ "Output". Ports are capable of two way communication. MP

Let's see what you have so far. It might just be a simple modification. Any chance you could put a sketch up here on the forum? MP

Kevin, look here for info on steppers: http://www.cs.uiowa.edu/~jones/step/ MP

Sotris, You can purchase the BAT29 here: http://www.danssmallpartsandkits.net/ http://www.electronicpool.de/list/index_B_A_BAT42_STM.html http://www.electronicpool.de/list/index_B_A__.html The part number is not in the correct order on the third link. You must keep scrolling through the parts to find it. MP

I have never looked at this as a leniency. I have always looked at it as versatility. That is what makes the op-amp so popular. But there are rules. There are lots of publications regarding the use of op-amps and complete libraries of circuits built with them. MP

Here is a site that might interest you. The author is using AVR with the program written in basic. Very similar to using the PIC and very easy to read. Perhaps you can pull some information from it. He has a serial port controlled stepper as well. http://home.planet.nl/~meurs274/ MP

Kevin, the zener in this schematic is setting a reference voltage at the base of the transistor. This is a common use in power supplies. MP

Steppers will not receive a serial protocol. They do not have any smart circuitry or logic in them. Just coils and the magnet basically. Whenever you see a serial communication to a stepper, the serial communication is sent to a micro or motor controller chip and the chip sends the data to the stepper in a parallel fashion. This is because the coils are energized in a sequence such as 1000, then 0100, then 0010, then 0001. (This also depends upon you using unipolar or bipolar). This sequence makes one step. To change the speed, you change the speed at which you send the bits to the stepper. To change the direction, you use the sequence above backwards. There are several motor controller chips that will do most of this for you and you only have to send a command for step and direction. The following is a link that might help. There is an in-depth tutorial on steppers here: http://www.cs.uiowa.edu/~jones/step/ Hope this is helpful and I apologize if I have covered anything that you already knew. I really do not know what level of information you need, so I might have been stating the basics here. Will you be using a micro or one of the stepper controller chips such as the UCN5804B? MP

What kind of information are you looking for regarding the steppers? I am not sure what you mean by protocol. MP

I like simple when I can get away with it. ;) MP

SGS Thompson made several power amp chips like these which were a TDAxxxx, where the x is a number. You might try a cross there, and then try to cross a TDA number over to NTE as they seemed to have quite a few of their equivalent parts. I will also keep looking in some of the data I have. Here is a site with several of the TDA data sheets. You might find a similar one: http://users.otenet.gr/~athsam/database.htm MP

No. That is not a problem. This is ok for an op-amp. You cannot look at an op-amp as if it is a transistor. MP

Further to my last reply: You should not connect anything "directly" to the telephone line. You should use the small transformer which is common for telephone line connection. In most places, if your circuit causes a problem with the telephone company's equipment, you are liable for the repairs. MP