audioguru

Ante, I can get only phenolic Veroboard in North America, it is the cheap, tan-coloured stuff that warps and breaks. Veroboard is now a new company, no longer part of Vero Industries. I think that it is called Verotech. Their web-site is nearly empty. I connect my 486 to my router with an ISA-slot, 1/10 LAN card. The router connects to the cable modem.

Ante, Yes, of course. I also notice that you do too. It all started when I asked a forum where I can buy epoxy-fibreglass Veroboard, like was available in the good old days (the blue stuff), since my Chinese supplier recently stopped carrying his very good copy. Sincerely, Mega-post goal, Audioguru P.S. I'm still waiting for my original coin, soldered-in, bios/clock, lithium battery to die, so I can replace it (I have one), then my computer will be good for another 10 years. I'm going to get a demo of that Extreme Hi-speed cable modem.

MP, Since my computer doesn't have this problem on any other web-site, then I complained, here. I thought that the problem, here, could be fixed, here. I didn't think that my computer had anything to do with it, like the errors that we get, here and only, here. Now I know where it is not very reliable.

Firefly, Use a TIP29 or TIP31 to replace the 2N2219. Their TO220 case can be bolted to a good heatsink. Since their current gain is less, change R15 to 100 ohms.

Xenobius, Good. I'm glad that you spotted and fixed your problem. So the 2N3055's emitter-base junction was avalanching like a zener diode, in series with the base-collector junction. No matter what voltage the output of U2 was providing, the output could not follow it down. Now you can remove those fuses which reduce the supply's performance: 1) Remove the fuse at the transformer's secondary, since its resistance limits the huge momentary current through the rectifiers when they charge C1, when the supply is loaded. 2) Remove the output fuse, since its resistance spoils the supply's regulation, when the supply is loaded. This supply has an adjustable current-limit so the fuse is not necessary. Xenobius, could you please measure the voltage across R1/C1 without any load, and again set to 30V with a 3A load?

Bob, 20KHz will be much better and we could choose a faster opamp. Also a logic opto will be faster than the PS2501 linear one. How fast does the current rise in your motor? Do you have a spec for its inductance?

Bob, The motor, opamp and opto delays are: 1) The motor is an inductor which will have an unknown delay. 2) The opamp has delays of 10 microsec. for rise, and 10 microsec. for fall. 3) The PS2501 opto has delays of 3 microsec. for rise and 5 to 20 microsec. for fall. Since these delays exceed 1 cycle of 50KHz, the output will not be pulses, but will resemble an average voltage that has a lot of ripple.

Hotwaterwizard, Yes, the disaster damage ratings are probably logarithmic just like your hearing's response to sound levels. Your eyes' response to brightness is also logarithmic. I made 3 triangle-wave generators to feed their linear ramps to red, green and blue LEDs, similar to the circuit in our projects section. I was shocked to see that the difference in brightness from when the ramp was half-way to when the ramp was maximum did not appear to be much more. I redesigned the wave generators so that the output current was the input current squared, then it looked fine. Back to sound, members in our forums are trying to use equal-steps digital pots as volume controls. Since these pots are not logarithmic, the steps at the top (loud) don't make much difference to the loudness and the steps at the bottom (quiet) jump with large coarse loudness changes.

Ante, I revised your circuit only because Bob needs to detect a motor current of 1A and more. Your circuit's LED current stays zero until the motor current exceeds about 2.8A. Regarding the opamp type, anyone using an old 741 in our circuits here will be very disappointed.

FireFly, Yes, the 44V rated TLE2141CP is a good substitute for the TL081 in this project.

OOOps, I always make this mistake: The gain of a non-inverting opamp is 1 PLUS the resistor ratio, so when 6A of current flows in the sense resistor then the voltage at the LED's cathode is 3.3V. If R2 is 910K then the voltage will be 3.03V.

Let me try attaching it again: ;D

Ante, I am sorry but your circuit has problems: :( 1) The opto won't be active until the current through the sense resistors exceeds about 2.8A. 2) The opamp's output will be 3.63V with 6A of current through the sense resistors. 3) R2-2 is not needed when using a 324 quad opamp. 4) You show the pinout for an LM358 dual opamp, which is the same as an LM324, except it is dual instead of quad. The data sheet for the LM358 is here: http://www.national.com/ds/LM/LM158.pdf I have re-arranged your circuit to make it better: 1) I have included the opto's LED in the feedback loop of the opamp so that the current through that LED exactly follows the current through the sense resistor, without any dead-zone. 2) I changed the opamp's gain so that the voltage at the LED's cathode is exactly 3V when 6A of current flows in the sense resistor. 3) I eliminated R2-2, since the LM324 and LM358 have inputs that can operate very well down to ground. My revised circuit is here: ;D

I said that already:

Ante, It depends on whom you ask. The marketing department of my ISP says one thing, and Microsoft and Bandwidthplace.com say another. But it is very, very fast.

If Ante's idea works, then mine will too.

InFLak, The piezo doesn't need triangle or sine-wave drive, a 555 or CMOS oscillator can drive the BU406 transistor. You don't need an H-bridge. Just copy the output wiring of the original. If the BU406 is bad then replace it with a good one.

Ante, Your circuit has a very good use of the very high input impedance of a CMOS chip. Do you think that it works as a capacitor voltage divider, with its antenna as a plate of a capacitor between the mains voltage and ground? Try it with an inverter as the input, which connects to a bunch of paralleled inverters that drive a speaker.

InFLak, You are correct that 2.7ms is 370Hz. Perhaps the ultrasonic vibrations are produced in bursts, with a burst-rate of 370Hz. The time of the pause between bursts will allow the water to re-coat the piezo. As you say, maybe the piezo resonates like an LC circuit at a very high frequency. It may not need an inductor across it since a piezo resonates strongly by itself, and even more if a tuned acoustical cavity is behind it. So in every period of the 370Hz, the piezo self-resonates at a very high frequency for half the period. You are right!

Yourwins, The 7812 is a 12V regulator with many transistors and resistors inside. A multimeter cannot measure if it regulates properly, but can tell only if it is shorted. I don't think that it can measure the difference of one that is blown open. The best way to test it is when it is functioning with a proper input voltage and load.

Hotwaterwizard, Never mind talking about PEAK. Peak power (also called maximum power) is just a method for marketing-guys to get a number that is doubled, since the power at the peak of a sine-wave (1.414 times its RMS voltage) is twice (1.414 squared) as much as RMS power. That's why a square-wave, or a volume control that is turned way too high, has the same peak voltage as a sine-wave and therefore has twice as much power (the distortion has the same amount of power as the fundamental). Decibels work in ratios, not "amount gained". The power formula is 10 times the log of the ratio. So going from 30W to 50W is about a 2.4dB increase. From 300W to 500W is also only a 2.4dB increase. The proof that doubling the power is only a bit louder is at your local high-end stereo store. Demo an amp that has a "stepped-in-dB" volume control and count 3 steps for a 3dB increase (twice the power).

Hotwaterwizard, Of course you can tell the difference between 5W and 20W, it is 4 times the power and a 6dB difference. But from 30W to 50W is a very small loudness change, only a little more than 2dB. You made a very good point about the speaker's box matching the speaker. If the match is poor or if the box leaks, then the bass response will be lacking or boomy, or any combination of the two (no low bass but boomy male voices, for example). Another important speaker spec that affects loudness is its efficiency. A 96dB/1W/1m speaker will have the same loudness as a 90dB/1W/1m speaker that has an amplifier that has 4 times the power. Stuee, You can't simply replace ICs or transistors in an amp to make it a bit louder (twice the power), but box matching, speaker placement (the sub in the boot (trunk?) is blocked by the rear seats) and speaker and amp wiring may make a much bigger difference. Maybe your amps are really only 20W RMS at low distortion, but are rated at 30W with 10 percent distortion (bad clipping). If your bridged amp is feeding 40 real Watts into your sub, then it would make better loudness with a 400W amp.

Nick, Ante's circuit in his reply #37 above, is a cheap and simple way to get -5V.

Fudy, Instead of building a TV station for your cables, simply move the vhsplayer to your TV and use your spare TV cables to connect the stereo audio back to your remote amp. This should work if the audio source has a low output impedance, otherwise the sound's high frequencies will roll-off due to the cables' capacitance. 20 metres is too long a distance for s-video signals.

Stuee, The 8 ohm car speakers are made for people who want to drive them from car-factory radios, or to parallel them and drive them from a real amp. I replaced the 20 ohm factory speakers (with magnets as small as a thumbnail) with 4 ohm 6X9s, and now my factory radio sounds very loud and clear. Reliability? My last car had the same setup running for 12 handed-me-down years with no problem, except that the car's lights dimmed a bit with the beat, and so did my ears. 8 ohm or 4 ohm? The difference is nearly twice the power, but it is only 3dB which sounds only a little bit louder. I doubt if you would hear much difference btween 30W and 50W. Your hearing is logarithmic, so 10 times the power sounds only twice as loud. Since the speaker's voice-coil heats and increases in resistance, it won't even produce twice the volume with 10 times the power.