MP

You are correct. But there is not a different schematic for each operation. I have attached the data sheet. The information is there for both types of operation. MP CM8880.pdf

Are you referring to the one I posted or the one russlk posted? MP

It is my understanding that this device is used to decode DTMF you "receive" so that it is usable. "Sending" DTMF is just a matter of sending tones. You would do this with a tone generator type of circuit. MP

If you download the Eagle layout files, you can move the parts on the board. Breadboards, Veroboards, etc. are boards with multiple holes on a 0.1" pattern. You could edit the board layout by removing the traces, then moving all the parts so that they match the 0.1" pattern. ..or you can delete the board layout and automatically generate a new board layout from the schematic, then place all the parts where you want them. After that, using the autorouter will put the line where you can see them and know where to put your wires on the breadboard. MP

You are correct that there is also a small heat sink on the board in the picture. The text shows that there is much on-board short circuit protection and does not mention heat, so I do not see the reason for it. Perhaps the author was playing it safe. Would those who have built this project please comment about the heat generated by the parts? MP

Yes, Pin 1 of the Parallel port is the strobe line. Pins 2 through 9 are outputs D0 through D7 respectively. Also, I looked at your bingo program with a text editor and it looked like there were some unremarked comments in it, like the first line was "clear". It might be possible that if you go in and make sure all comments are remarked, it might compile. This was just a quick look and I did not get much farther than that. MP

Kasamiko, if that will not work for you, here are the eagle board and schematic files. If you do not have the free eagle layout editor, you can get it from the dowmload links on this site. You can edit these files with this version of Eagle to make the design more specific of your application. MP ICL7107_Files.zip

Would like to see postings of used Bench Test Equipment. I think we all could use another meter from time to time. MP

If you are using a 6A rated bridge rectifier in place of D1 through D4, which are rated at 2A, then you are never going to need a heat sink for this rectifier bridge. It will never work that hard in this circuit. The Heat Sink in the picture is for the 2N3055. The data sheet for this transistor gives some information regarding heat transfer. Most heat sinks are also rated for their heat transfer. As a general rule, if you are using the upper limits of the current rating of the power supply, it is going to get the power transistor hot. If you are only using less than 1 amp, you can probably get by without it. MP

No. That is not what I am saying. Let me explain this in a different way. If the transformer is capable of putting out 120VAC at 10A (remember, we are talking about a step up transformer) then with a voltage doubler added to it, he would have 220VAC at 5A, which might still be sufficient for his design. On the other hand, if he has 120VAC at 1 A and he needs 1 A, then he is not going to be able to use a voltage doubler as it would then reduce his current to 500 mA. These are not actual voltages nor are they a suggestion. They are simply numbers which are easy to relate. But I think that this example will put forth the idea. MP

It is true as Ante has pointed out that the current goes down as the voltage goes up. However, if you have a sufficient amount of current to begin with, dividing will be no problem. The end user must make this calculation in the design. I would never do this as a bench power supply where you might come across current hungry circuits, but it is certainly feasible as a trick to bump up the voltage in a device that has sufficient current to absorb the loss. I would not go as far as to say that you will not have much useable current, though. This is dependent upon what you are putting into it. Which is directly dependent upon the VA rating of the transformer on this particular project. MP

John, the ones you have purchased are polarized. The black band on the side with the dashes indicates that this lead is the negative side. For the application you are using them on, I really do not see where this is going to be a problem. Perhaps someone would like to comment why these have to be non polarized to light an LED? MP

Just a quick look at the circuit above...looks like you could use 2N3055 in place of the MosFets if you use a resistor to ground as discussed earlier. I think you could also get around the SG3525 with a 556 timer IC. One would have to compare the data sheets to get the correct pin out and frequency for the clocking. This is just a quick look at the schematic and I have not looked at any data sheets on this. Any comments welcome. MP

ok, I apologize. I should have said they are clear to me. Not everyone is as familiar with data sheets as others, so I can see where there might be some confusion even after looking up the data sheet. Still, the manufacturer will give you technical support. All you have to do is ask. MP

Great! When do you think you will be posting the schematic for us? MP

Here you will find the answer to molding plastic: http://www.pulsar.gs/4_si/3-UniVac/_univac_frameset.html Would be interested in knowing how you do when all is complete. Please let us know. MP

Indiglo, your circuit will simply change the electrical data to light and then back to electrical data again. The reason to do this is normally to send data through long signal lines without electrical interference. You should not have to worry about sync problems with an analog signal. The only bandwidth problems you might encounter are those of the amplifier that converts the signal to light and the one which converts the signal back again. If you start clipping the signal, then the conversion will sound awful. One area of concern is signal loss. At audio frequencies you will see a 0.25 decibal loss per km for good cable. Lower standard cable can be as high as 3 to 4 db per km. The phone company gets around this with repeaters. Some research on telephone fiber optic practices will help you, I think. As Kevin was pointing out, you can digitize your signal to give it more strength and speed of transmission. MP

Glad to hear it. I always have a concern when working on high powered circuits. In regards to the capacitors, and any of these parts for that matter, you can use higher rated parts. For example, a 220 Volt rated capacitor will work just as well at the lower voltage. This rating is a maximum voltage rating. MP

...as he said, he needed gain up to 20dB and roll off at 40dB/decade. Op amps are the best way to go to achieve this. If you can provide a similar circuit as you have mentioned using only transistor capacitor transistor capacitor, please post it so that we can see. I think that it is only fair on this forum to ask if you are going to argue with proven design or a posted schematic that you should post your alternative method. Electronics deal in fact, not opinion. MP

Here is what is inside the common LM741 op amp. With this in mind, your post does not really make a lot of sense. Perhaps I misunderstand? MP

Many of the web postings you see are just the schematic from the application notes of a manufacturer's design. If you go directly to the data sheet, the reason for the added external components is usually pretty clear. MP

You can buy these parts at your local Radio Shack. Depends upon where you live. Online, my most common sources are: www.digikey.com www.mouser.com www.circuitspecialists.com www.allelectronics.com I would also like to insert a little warning here, though. If you are not familiar enough with electronics to know what the symbols mean in the above schematic, should you really be taking on a circuit with mains power as a beginner project? Mains power can kill you. MP

It would take far too many transistors for a similar circuit to make such a design feasible, stable, and allow this kind of control to bandwidth, center frequency and damping factor. MP

http://www.protel.com/product.htm MP

It has been quite some time since I have used modulo X circuits. If you could post your schematic, perhapsw we could all have a look and see if we can help. In the meantime, I have found this link that might be helpful: http://www.ccse.kfupm.edu.sa/~masud/text/lab7.pdf I also recall seeing another post here in the past about someone building a clock circuit like this. You might find the other post with the search feature of this site. Then you can contact the author of the post through the message system. It will send an e-mail to them directly. MP