MP

As additional information for those who were interested in the serial port information: The Lynx technology transmit and receive chips use 3 Ma typically and actually 1.5 mA on average. Since I would never take up two ports on the computer to run one device, I would look for a low current consumption device such as this. MP

...of course, the answer is yes. He can certainly use the USB power pins as a power supply. There is no association between the power pins and the data transmission lines. They are just on the same connector so that they can power the device connected. Current limiting with a resistor is a good idea since you are connecting to the Computer internal electronics. MP

No. It is not. MP

You can actually tap the voltage you need from the serial port unless you need a lot of current. AtMega chips only require micro-amps. It is the additional circuitry that requires additional. Here is a schematic of a 5 volt tap from the serial port. MP

yep....later there was a merger. Then they went out of business altogether. MP

The original design did not even use a pot. I'll stand by my first comments since I know how this will effect some devices that might be plugged into it. If you can't find the panasonic pots, try the clarostat 585 series. They are available at Newark Electronics ( www.newark.com ) as part number 585DX4Q25F103ZP at $2.48 each. No waiting. Or just build the original which did not add a resistance path to ground ahead of the input cap. In this case, you rely on the volume control of whatever is plugged into it. Part of your parts availability problem is due to the pot having an on/off switch. Another alternative is to purchase an audio taper pot without the on/off switch and use an input jack with an additional leg that sits against the ground barrel of your cable. Attach the ground of your battery to the additional audio input lug which is only grounded when you have something plugged into the unit. This will also keep you from losing batteries if you accidentally forget to turn it off when you disconnect. (Example below). This is easiest if you are using a mono input. You can use a stereo jack. However, if you will be connecting two of these circuits to a stereo jack, you can still get jacks with additional connections in them. They are just not as common. MP

That would depend upon what's in the electronics of what is connected to it... ::) I would suggest that you use the correct value and just get it from another source like mouser.com or one of the surplus parts houses. When you start changing the resistance of inputs and/or outputs, you sometimes end up with strange problems that are hard to determine the cause of. Keep the correct values. MP

Yes. Try posting your PIC questions in the microcontroller area. You aren't really discussing the diode tester project, so you are in the wrong area. MP

Syed, Please check your email. Take care! MP MODERATOR EDIT: The original project has been corrected in the projects section.

Hello Herman, You will not be able to have a direct conversation with the author of this circuit. The original author is "Smart Kits", but it is a very old kit design and lacks modern principals and newer chips that were offered after the initial design. There are new chips on the market that would do the job much better. However, the point of this area is to discuss what is already here. This thread deals with questions to build this project and questions and answers anyone has regarding it. Audioguru has suggested a lot of changes, so you might mention which version you are suggesting additional changes. Note that "Smart Kits" are not real elaborate designs. They are simple kits to help beginners learn something about electronics. This thread has turned into a major re-design fiasco instead of simple questions and answers for those who are trying to make the kit. I would have prefferred that those who wanted to discuss a re-design would have taken this subject out of "Projects Q/A" and made a topic in the appropriate area. This approach would have been more beneficial to other members. If I ever see myself having lots of spare time, I might move posts around so that it is more organized in this way. I get lots of emails and PMs grumbling about how this topic is no longer helpful to one trying to build the project and that it is much too long to read through. Perhaps we should open a new forum named "re-design" ;D (That was a joke, AG) MP

vivek, we do not have a project on this site for such a large consumption. Here is a website that fully documents a 2KVA that has a modified sine wave: http://www.technology.niagarac.on.ca/people/mcsele/i2k.htm This project uses the microcontroller as I had described above, but don't worry if you have never programmed a PIC. Everything is on this website, including the code for the micro. I think you can even contact the author with questions. MP

AN920: It says a 50% duty cycle is not guaranteed. Period. It does not say that you get a "perfect 50% duty cycle" anywhere....which is what audioguru says the datasheet says. vivek: to get a sinewave inverter, you would use a different technology. You cannot use a sinewave and amplify it like a squarewave. Too much heat loss. Many manufacturers use a microprocessor to digitally simulate a sinewave in a switch mode. MP

Amazing....since I posted a picture of part of the datasheet. Where did you find the word "perfect"? I performed a search of the pdf and found 0 instances of the word "perfect". I also performed a search for the word "exactly". Also, there are 0 instances of this word. However, I do find a statement in the data sheet that says a 50% duty cycle is not guaranteed. You have a pretty good nack for reading things into a data sheet that do not exist....of course, I think I have made this same statement to you several years ago.. oh, by the way...what you explained was how the IC uses a digital divider to produce perfect compliments of the two signals Q and Q-NOT...Not how it produces perfect square waves. There is quite a difference. I know I am wasting my breath to explain all of this to you, but there are others who might like to know. MP

In 1982 it became "Computer and Electronics", then went out of print in April 1985. Many of the editors and authors moved to a new magazine named "Electronics Now". Many readers thought that this was just a new name for the magazine since the authors names were familiar. Look for "Electronics Now" for the same type of articles that you saw in "Popular Electronics". MP

mik3ca, Here is a standard circuit of vu meter that is made with transistors. Hope it helps. MP

Have you asked the author of the circuit? http://www.redcircuits.com/ MP

Interesting that you can read that into the data sheet when it is not there... MP

There is nothing in the datasheet that proclaims a "perfect 50-50 duty cycle. In fact, the manufacturer puts a disclaimer in the data sheet that a 50% duty cycle is not guaranteed. Fortunately, for a square wave inverter, you do not need a perfect square wave. You don't even need a perfect 50 hz or 60 hz. The square wave inverters are the worst of all inverters out there. You will see a large variance from one to the other. If you want to build something that will be useful, build a sinewave inverter. MP

Yes. I thought my answer was pretty clear in that regard. MP

defaced, Your unloaded output voltage measurement is pretty meaningless. You need to measure the voltage loaded to get an accurate measurement. Also, if you want a well regulated 12 VDC supply, you should use a regulator. Most regulators require an input voltage which is 2 to 3 volts (or more) above the output voltage. Just get a 7812 voltage regulator for this power supply and you will have exactly what you need. If you use a transformer with an 8 volt secondary, you will not have enough voltage after loading occurs on the output. MP

Tkjas, You seem to have quite an interest in Transformers. Here is a link about winding transformers. It might have some information in it that will prove to be useful to you. http://geek.scorpiorising.ca/windingtransformers.html MP

Many designs use Buffers, many use Inverters (NOT gates) to produce a nice square wave. I have also seen AND and NAND gates used to do this. Digital gates are good for providing a square wave. In fact, many circuit designs employ them to square up other wave forms that are not clean enough for a good digital switching action. The nice thing about using digital gates is that they have a good fan-out. Thus, you can parallel and/or series them to get a stronger signal if ever needed. MP

I have used the LM324 in many audio applications in the past. For the specifications that you have given, this chip will be fine. It will not give you really great results that you would get with a newer low noise op-amp. But it will give you a descent mixer. Especially at 1 KHZ. MP

The purpose of offset null is to compensate inconsistencies inside the op-amp that do not allow it to zero out when it should. It is not intended for the regulation of varying output loads. This is done through impedance and/or amplification methods. Perhaps I did not fully understand your post, but it does not sound like you are using the offset null correctly. MP

Hustla, Welcome to the forum! There is a circuit in the projects section of this site that might get you started, or at least, give you ideas on your own design. You can access the projects on this site with the blue link at the top of the page titled "Projects". Hope this helps get you started. MP