>I think Leo already has the USB interface working. Alternately, by using an OP Amp without the feedback resistor and driving a transistor at the output, effectively makes the OP amp a voltage to current converter or a voltage controlled current source. That means anyone can use this simple setup to connect an LVDT to a standard game port or older conventional USB adapters. I think we should start calling it the "Mike" MVDT...in honour of its creator. Hence forth, all "home made" LVDTs will be referred to as MVDTs! All in favour say "I"...."I"...motion is passed. :DStill no luck finding suitable coils. I have a few more catalogues to sift through. If we can get "repeatable" coils with well-defined inductance, we can better optimise the freq required to drive it and in turn the output signal.Brass tubing is readily available at hobby shops and can easily be soldered together. We can thus easily make sealed casing to house the coils in.-Leo

For a little more work but less money...... I remember winding electro-magnet coils as a kid for a diy project. The method I used then should work for this - use the plastic bobbins that go in sewing machines. Stack three of them on the bobbin winding post of your wifes sewing machine. Put three spools of wire where they can unwind freely, then get a bit of cardboard or plastic and punch three holes in it the width of the bobbins apart. Feed the wire through the holes onto bobbins. Then, as you press down on the sewing machines foot pedal, move the card slowly up and down to feed the wire smoothly. That should give you three identical coils.Richard

Not a bad idea. One thing to keep in mind is the desired stroke length. The secondary bobbins should each be as long as the length of the full movement of the core. The core length equals the length of one secondary bobbin plus the primary bobbin. The core is always in the primary bobbin, but if moved to be 70% in one secondary, then it should be 30% in the other.I have built and tested some basic electronics for use with a homemade LVDT. It outputs 0 to 5 volts with a moderate range of adjustments for both span and zero.Using non-selected components (meaning parts that should match, did not), and not adjusting the innner workings of the circuitry (other than the span and zero), I saw a moderate increase in non-linearity for the combined LVDT and electronics to 2.6% full scale. I expect that linearity better than 1% full scale is quite achievable by taking care to wind the LVDT a bit more evenly, and by either selecting matched parts or including adjustments for balance.The schematics are posted in a new page linked to the original LVDT page.Mikewww.mikesflightdeck.com

"I" :-)Just done with testing of my first MVDT prototype ;-)Experiences:When cutting the brass pipe at first, i didn't think of how I would spin the winding onto it. Note to protocol; Add approx 20 mm of brass tube as mounting in the drilling machine.Olles MVDT project:1. try to find a better core coil than I used now, 4mm iron rod. Will try the next MVDT with a 6 mm one and a little wider brass tubing. More iron in the core is better right?2. sine wave oscillator. Done the test with 1kHz timed by a 555. Square works, but the windings emitts quite much jitter at induction.3. anxiously wait for the encoder circuit and hopefully a usb adapter.4. whohoo!!!/ Olle

WOW. That was fast!Mikewww.mikesflightdeck.com

>"I" :-)...:-beerchug >3. anxiously wait for the encoder circuit and hopefully a usb>adapter.Keeping in the spirit of things, I'll code a 4 axis 8 button USB device on a single chip based on the smaller cheaper PIC16C745 chip. I'll make the precompiled code available for you guys to program your own chips. Just give me a few days, I'm really tied down with some work.So start ordering those free samples from Microchip. ;)It'll be super simple to build and use only 1 chip. You'll only need 3 or 4 caps, 1 resistor, 1 resonator and a USB connector (or connect the wires directly to the board). The analog axes will be the ADC pins of the chip. So if Mike's circuit can provide at least 1-4 volts at in range, it'll be more than enough for a good range at the output.FYI - PIC programmers sell as cheap as $6 each or build your own for free.-Leo

That's great! Thanks.What frequency for the resonator?Mikewww.mikesflightdeck.com

It

Thanks, Leo. I've got a UV eraser somewhere. I just hope it's not so deep in the pile it's started to compost.Mikewww.mikesflightdeck.com

LOL!Sounds like the mess in my basement that my girlfriend is starting to poke me in the ribs about.I can probably use my UV PCB exposer to erase them. Just ordered a few samples from microchip, lets see when/if they arrive soonThanks for your generous sharing of your knowledge!!!Cheers!/ Olle

Gaa!Just did a Eagle schematic of the sinus oscillator and made a PCB layout.... Tough job to fit that on a single sided PCB.... *sigh* Have you done it Mike?/ Olle

Hi Olle,I have not made a circuit board for it. I prototype "dead bug" style with the chips inverted on blank PC board material and air wire the parts.It's not pretty, but it's fast.Mikewww.mikesflightdeck.com

This is what im doing right now.... http://forums.avsim.net/user_files/40600.jpgWorse than jigsaw puzzles, and i hate those... Will give it a try and then on to the decoder circuit :-)Cheers!/ Olle

Olle,How successful is the auto-router? Mikewww.mikesflightdeck.com

You'll only need the UV eraser in case I make a mistake in the firmware...unlikely ;) or if the programming fails and you need to start over, but I find that rarely happens and I'm using an el cheapo home made one.Samples come in clean and ready to burn, so you may want to just leave it...wherever it is for now and gamble on a problem free programming session. Live on the edge... (-: -Leo