MP

Steven, do you have a picture that you could upload to the group? It would be great to see the finished product. MP

Normally, you would use ADC converters for connection to a microprocessor. There are many documents regarding ADC conversion with a search on google. I would recommend that you use a pulse to voltage converter and use the voltage to trigger your relay from a set point. (less circuitry involved). Look at this article and included schematic: http://www.discovercircuits.com/per-volt.html MP

I do not have protel, but it might be that you save the file, then change the extension to whatever it is for protel schematics. MP

Steven, I have seen several posts from you regarding the projects you are working on. Why don't you upload them to the forum? I am sure several others will be very interested in them also. If the upload area is not up, you can e-mail them to Mixos on this site. MP

Yes, Like I said on the 18th, "...of course, there is also the old standby. A small float connected to a switch that activates a relay." This is much simpler to do. And you do not have to use metal parts for the float as Steven has indicated. Good luck with your project! MP

I think we need more information. You know a continuous 240 VAC at 20 amps is 4.8 Kilowatts don't you? You could burn down your house with this much power dissipation. Be careful. MP

I looked around to see how others have done this. Here are a couple of links: http://www.parallax.com/dl/docs/cols/nv/vol1/col/27.pdf http://hawthorn.csse.monash.edu.au/~njh/electronics/watersensor/ These do not seem to be real simple switch methods, but might give you a platform to build upon. MP

Alternating current will also corrode. :) MP

You will need about 185 feet of wire. (The short answer). ;) MP

I am not really following the change in capacitance theory on screws coated with plastic, but you did make me think of some other ways to accomplish this. You can use a pressure sensor with a tube from the transducer to the water. As soon as the water falls below the end of the tube, the pressure will change to be equal with the outside ambient barometric pressure. Another way is with a temperature bead if the water is a different temperature than the outside air. And thirdly, how about a laser or IR detector that shines into the tank near the top and is monitored by a receiver on the other side? When the water is low, the amplitude should change since the angle of refraction will change. ...of course, there is also the old standby. A small float connected to a switch that activates a relay. :D But please tell me more about the capacitance method you are describing. I would like to understand it better. MP

Then you are probably looking for application using a Transconductance Operational Amplifier (OTA) such as the CA3080A or similar. This device can be used like a variable resistor by the control pin. It is used widely in music applications for effects filtering circuits and VCA applications. MP

Yes. Believe it or not, they 'did' have this technology in 1984. ::) My scope is not much newer than this. How time flies, huh? MP

Did you also see the other post in this area regarding where to get monitor schematics? MP

I would suggest finding the schematic and check the voltage from the switch to the internal board. You need to know what the LED is connected to. If it is connected to the power supply, then it could be a power supply failure; even a bad on/off switch. If the LED is connected to the processor board on a digital monitor, it is most likely due to the processor going into constant reset. This could be many different things. The first step is getting the schematic and following the power and signal paths. MP

I hope I am not misunderstanding you, but ohm's law is the rule no matter what the circuit is. V/R=I. You must take into consideration the resistance of the total circuit. If the resistance of your circuit changes or the voltage changes, then the current will change according to the formula. In regards to capacitors, the energy (in joules) stored in a capacitor is given by the formula E= 1/2(C*(Vsquared)). Here is a link that goes into more detail about capacitance. Perhaps this will help you complete your project. http://en2.wikipedia.org/wiki/Capacitance Please let us know about the results. :) MP

Yes, here is a diagram. Two ways to do it. Both are the same. MP potentiometer.pdf

If I translated this correctly, you are talking about the unit having very very low current output? If this is the case, I see that you have 60 volts before your voltage goes into the 1.8K resistor. Using Ohm's law, 60/1800 leaves you only 0.033 Amps of current into the 12 volt regulator. The regulator, 2n3055 transistor and the rectifier bridge can handle more current, so I suggest changing the value of this resistor to give you more. Does anyone see anything else that should be mentioned? MP

In reply to the question asked by Derfly, you can connect the potentiometers in series. More importantly, for the fine adjustment, you will want to use a 10 turn or a 15 turn or even possibly a 20 turn pot to give you the accuracy you want to achieve. This should be on the smaller value pot as you want maximum number of turns for smallest voltage change. Hope that helps a little. MP

The following link might be an excellent building block to get you started. It is a low voltage (0-1V) voltage to current converter with single supply rail. See Fig. 1 for the schematic. http://www.elecdesign.com/Articles/Index.cfm?ArticleID=2985 Happy soldering! MP

If the link does not work, just go to www.allelectronics.com and use the search box. Enter pm-200 for the search. MP

Firefly, they are just trying to say the supply voltage must be a fixed voltage. The other input is the measured voltage and this is what will be displayed. In other words, you would want to add a 9 volt regulator right after the rectifier bridge to supply this unit and the measured variable voltage will go into a different pin on this meter to display the output voltage of your PSU. Here is a link to the one I have just purchased. Much better price. In fact, I have not seen one for less. It has different jumpers for decimal point on voltage ranges. 0-2mV, 0-20V, 0-200V, (up to 500V range, I think). http://www.allelectronics.com/cgi-bin/category.cgi?category=385&item=PM-200&type=store MP

I know nothing about EEG, but in instrumentation it is common to convert the voltage to current and read the current or even convert it back to a voltage in order to keep the noise level to a minimum. Hope it helps you a little. Another thought is that fiber optics are pretty much immune to noise. MP

Device is made of a crystalline substance which creates charges of electricity by the application of pressure and vice versa. ;) MP

Billy: The regulator might get hot with this amount of difference, so you should add a heat sink. Also, in regards to the capacitors, when you add a capacitor to the input side of the regulator, isn't there already one there for the other part of the power supply? When you put two capacitors in parallel on the same line, it changes the value of capacitance and will actually cause less filtering in many cases. Check your values with the capacitor parallel formula (Ctotal= (1/(1/C1+1/C2+...1/Cn))). You will probably not want the additional one there. Be sure that all capacitors are well above the max voltage range. I usually use the times2 rule when possible, but this is not necessary. This is only my own personal safeguard. Firefly: You should not need additional transformers to run a fan or meters. If your existing transformer is capable of the added current usage, you can tap into it just after the rectifier bridge with a regulator or a zener/resistor for the correct voltage drop. MP

Yes, this is solid state. It is just not a relay. I think it is a good circuit to achieve the same goal. Many times someone will refer to the term relay as a switching method instead of an actual device. This is a vey good circuit and I for one will add it to my library. I have been thinking of some changes on my swimming pool pump circuit as well. Thanks! :D MP