bogdan

why not use ultrasonics? put a senstor at the top of the tank and it can determine the distance between the sensor and the water. or, i am thinking of another way, with the capaciatance switch. maybe a better rensor would be to run 2 insulated paralel, horizonatal wires in the tank. put them very close together. water cobing between them means an increase in capacitance. i am thinkting of another basic method. use a magnet attached to a floating device, and enable the floating device to moove up/down on a vertical wire at the edge of the tanks. on the other side of the tank you could have some reed switches.

well, i know i can do it that way, but what i want is a circuit that will not need external power. just from the cap.

just a little modification. for 9V you can put 3 leds in series. so you could use 9 leds or have a series of 2 leds and 2 series of 3 leds.

what do you mean my SOA??? well....i forgot about the ic's. maybe they can be replaced by something else? soooooo.... in conclusion the idea is to put 2 transistors in paralel....right? and change the bridge.... yes, you are right, there is a small difference in price between a 10A and a 35A bridge, but still, i think that a low drop one should be used....

yes, i think that a 10 or 15A rectifer could be used.... why not use a bridge from schotty diodes? expensive, but more performant. a good transformer would be a toroidal one, probably a 30V, 200W would be suitable. i think that having 30V a.c. output rather than 24V. if we use 2 transistors in paralel, than a resistor must be bonnected to the emitter of the transistors. cannot use them directly. also, 2 heatsinks must be user, or maybe a bigger one for the 2 transistors. like mentioned before, the putting the 2 transistors on a heatsing will not increase tha current. since the power lost as heat on the transistor is dependent on the current, having half of the current troug one transistors means that only half of the power is disipated on that one. and there are 2 transistors, you still have the same total power didpated. anyway, i would be curious of something. say that i will cool a 2n3055 transistor with water and maintain the temperature at a low value, less than 50 degrees, do you think that i could make a current more than 15A pass trough it? i think that it is possible...but not tried it yet.

here is a tip.... the probes don't corrode is you apply an alternative current on them. the reason why they corrode is because if electricity flows in just one way, then a process of electrolises starts. water gets split in O2 and H2 and these react, especially the O2 with the probes. also, i suggest using some stainless steel wires for the probes, or better aluminium. it doesn't corode that fast.

yes, lamps are not more reliable. i think that the best option here is to either put tu 2n3055 transistors, but it think that tha will require having a 30V a.c. transformer to obtain 30V at the output, or to use a highter power transistor. or, maybe what about using 2 2n3055 transistors in paralel? i have seen this in many schematics. maybe it will work better than having 2 transistors in series?

not quite like that. you see, considering the capacitor charged, it has a stored amount of electricity Q=C*U. and an energy of E=C^2*U/2 . now, Q=I*t, where t is time and I is the current trough the cap. if you discharge the cap trough a resisotor than I=U/R but U changes because the cap discharges. U=Q/C, but Q2=Q-I*t so U=(Q-I*t). if I is constant, than the voltage across the cap is decreasing in a liniar way. but if you discharge the cap trough a simple resistor, than I drops with the dropping of U. this way thec voltage on the cap decreases slower and slower. now....what i need is a circuit that can draw a constant current, even is the voltage applied on it is variable(of course, in limits).

nope, you did not understand me right. :P i was suggestiong to use the heatsink and the transistor that are already there and another resistor in series with the transistor, wich will be short-circuited(the resistor) when the voltage required at the output of the power suply is highter. what i was trying to say is that for the resistor, a heatsink is not required.

hello! i am using this method too.... only...a bit different, i don't have a laser printer, so i have to photocopy the board. but i tried with laser printers and it works fine. i photocopy the circuit printed from a jet printer on some sperial paper, similar to the one from magazines, acutally the guys from the copy shop use it for printing invitations on it and cards. it works well. though, there is something i do different form what it is presented on that website. immediately after ironing, i drop the hot pcb in cold water. it makes that nice sound of instant boiling of water. the results that i have are good. still i sometimes have to do some touchup for some tracks with the marker. also, just a tip, for making the tracks from the edge of the pcb stick better, it is a good idea to surround the whole pcb with a thicker circuit line, witch you can clean after you take the paper out of the pcb. and another thing, cleaning the ink after etching with acetone is better, with the sponge you seem to scratch the tracks.....

well, yes, the realy and resistor and control circuit(a low power transistor, a zenner and some resistors) can be more expensive than the transistor itrself. but what about adding the heatsik? you will not need a heatsink for the resistors. yet, i think that the power resistors can be more expensive. what about using something else in place of the resistors ? like car lamps or other types of lamps....?

there is a strange thing. even though the HM205 is a good and quite performant osciloscope, i can't find any info on it. why don't you try emailing the manufacturer. maybe they have the manual and can email it for you.

i saw something on tv once. it was an implantable device. as power it used a coil wich was generating power from a magnetic field wich ws generated by the chip readrer. a cap was used for filtering. as suggested, RF is used too.

well, instead of using the LCD and PIC for dispaying the voltage and current, don't you think you could use a voltmeter and ampermeter kit wich display on 7-segments leds? also, another suggestion. for the negative you could use a LM317 regulator, as it can provide 1.5 amps. i am not sure how it will cope with low voltage and high current since you have a higi input voltage, more than 30 volts, than you will have a lot of power disipated on the reg. might use 2 in series as suggested.

ok. i have a suggestion. what if the 2N3055 transistor could be replaced by 2? this will lower the dissipation ok each transformer. but the drop on the transistors means that the output will not be as high as 30V.... or, another suggestion. put a resistor in series with the transistor. and a relay with a control circuit. when the output voltage is more than 15V(let's say) then the resistor is shortcircuited by the relay and so you can get the maximum voltage. when at the output is lover than 15V then the relay is OFF and some voltage gets dropped across the resistor. this way you minimise the power dissipation ok the transistor. and for the heatsink...i think that mounting a small fan, maybe one similar to a computer cpu fan coud be used. having an artificial air flow cools the transistor better than a large heatsink. and for getting 12V for the fan, i would go for a 7812 regulator. it is cheap, and for the current that a fan will draw, less than 200mA it is very good. well, hope that my suggestions will do some good.

it seems strange. for the first 2 datasheets i get: File Not Found Microsoft VBScript runtime error '800a0005' Invalid procedure call or argument: 'Mid' /error/404.asp, line 169

looks like the datasheet doesn't work. maybe it works for you. i get file not found.

well, i found it look at the bottom of this page http://www.scientificindia.com/hm205-2-osci.htm is this what you are looking for?

i need to build a constant current load, to demonstrate that if a constant current passes trough a capacitor, then the voltage across it increases or decreases liniary. the problem is that i don't know how to build this. the caps will be charged to max 16V, and if i can get a constat load over an interval of about 5V then it is very good. but how can i build such a circuit? i know that if it connect a LED trough a BF256 transistor, and connect the gate with the source, then the current maintained trough the led is between 10 and 15mA for voltage from 5 to 30V. but how can i make a circuit that draws 1mA?? any help is much apreciated.

have you tried there website? i think it should be there!