Whites Surf PI schematic

[porkluvr]

Here is an almost complete Surf-PI circuit. I think that the one-short pulse widths may be a little short compared to the real world circuit, so keep that in mind.

I have included a small parasitic circuit to try and simulate a target. This might not be as good for realistically replicating a target response as it is for verifying that your amplifier chain has the correct polarity sense. Say, in case you wanted to start playing around with different configurations you might want to reverse the sample1 and sample2 inputs to the sample amplifier and see that the output will slew the other direction from before. Or, if it doesn't change direction you might want to find out why.

I replaced the TIP32 with IRF9640. I was sort of baffled when as I saw the TIP32C flyback peak at about 150V because that device is only rated for 100V. Now, I don't have to ponder that anomaly - I just ignore it. (Hey, there are only so many hours in the day.)

My NE5534 model is like most other simulation models of parts with compensation or nulling, in that only some of the pins are modelled. Here we have the compensation pins modeled when they are not used, and the offset pins that we could use are not modeled.

I have included the CD4000 library without change but I did not include the complete symbols libarary which is available at the LTspice Yahoo users group.

The original NE555 symbol provided with LTspice is in the MISC parts folder. I modified that symbol to make it smaller and easier to wire for the majority of schematics that I've seen. The model is the aame but the symbol is different. You can either use my symbol or else move some wires around and use the default 555 symbol.

I think this should run so long as the parts and symbols are kept in the same folder as the .asc file. If the parts don't fall into place then look at the screen shot for parts placement.

edit: If the BAT54 diode is not included in standard.dio then use any schottky available. If I left anything else out, let me know and I'll make it right.

[bklein]

For those interested, check out patent 5,414,411. It covers this circuit and has a good description of the various sections. Something must be wrong with my detector as it describes the coil output of 100-130V and mine is 87V. I'll make up a coil to substitute and see if things change.

Barry

[porkluvr]

Make sure your output pulse from the 555 is about 50us. The -currently available- CD4093 model needs some major adjustment but the LM555 model is pretty accurate.

If you have 50us, make sure your resistors R4 and R5 are 100 ohms, and R3 is 1k to drive the 2N3904. It might be easier to replace the two transistors (starting with the 2N3904) than messing with replacing the coil!

The simulated waveforms in the transmit section should be pretty close to what you would see on your scope.

Your coil/cable should measure about 1.4 ohms (and 230uH). I think it would take a serious coil malfunction (something you should be able to measure) before it would affect the flyback as drastically as you say.

My "armchair troubleshooting" advice is usually wrong but I've still got to try.

[bklein]

I temporarily replaced the TIP32B with some sample TIP32C parts I got from Jameco. One of these brought the receive pulse to ~130V as desired. The thing is that without a curve tracer I don't know how anyone would suspect the transistor... With a m-cubed semiconductor analyzer the Hfe's of the various parts vary quite a bit but I see no correlation to the pulse amplitude. With my Huntron Tracker I see distortions in the original B part and some of the C parts but the "good" part has none. I have yet to try a mosfet or see how this all affects detection distances. I suspect the TIP32B part got damaged from the high pulse voltages outside the Vce spec. The tip of the pulse is truncated where as with a good drive transistor this drops to a sharp point. My drive signal is 56uS.

[porkluvr]

Barry has informed me that the LM358 model was left out from my project post. Here it is, along with appropriate symbols.

Most IC manufacturers have models for at least some of their devices on their websites. Many times the model's pinout will be exactly described in the model's header. If not, well then it may be time to exercise one's cursing skills.

So you then need a symbol. All that is often needed is copying a similar symbol and making the appropriate attribute changes to match the new model (and of course renaming the copy with the appropriate filename). New symbols aren't hard to make, either.

LTspice will need to be restarted before you will be able to use new symbols, or before changes to various .cmp files will be recognized.

[bklein]

I have attached delay.jpg to demonstrate my problem understanding the preamp circuit. You can see that the input and output are delayed by at least 6uS. Perhaps this is due to op amp slew rate? This is not a coil speed issue but a circuit delay we'd rather do without. You can see that I have reduced the op amp gain considerably by replacing the 1K neg. input resistor with 100K. I also deleted the input diodes to negate the weird things I was seeing with them incircuit. Maybe this makes sense to you guys, but not to me....

Barry

[bklein]

Ok, no comment means my brain cells are screwed up...
I temporarily fixed that and can now see things line up as I would expect to see.

[TH Jim]

The beeping problem solved

Hi Guys,

Reading through some of the earlier posts in this thread I realised that a few of us have experienced the strange audio pulsing at anything from 1/2 second to once every few seconds. Anyway I think i've found the cause - it's RF / mains hum getting in through the headphone cable (or battery cable if its long like mine). To kill off this interference just put ferrite beads on your cables near to where they connect to the PCB - it worked for me

P.s Don't put ferrite breads on your coil cable - that will be bad

[bklein]

Thanks for the tip!
I haven't looked at eliminating the noise in mine yet but I had thought it was getting into the coil itself as if I moved its orientation it would affect the noise amount. The SD2000 schematics on site have a 1uH inductor in series with the coil. I think something can be done but I haven't looked at just what yet. Did you put one bead on the ground/shield as well?
Some op amps like to rectify rf thus you hear it. Problem with guitar amps. I lost track of which op amps don't do this... too long ago for me.

[TH Jim]

Yes there is definately noise getting in through my coil as well, But what can you do about it without affecting the reflected pulse? I did read somewhere on this forum about someone using a Balum transformer to eliminate noise in the coil / cable, but dont know what results were like.

I have 1 bead on +- shielded coax that delivers power from my hip mount battery pack and another on a similar cable that returns the audio signal to the battery pack (where my headphones plug in).

Regards, Jim.

[bklein]

I'm just throwing this out there without trying anything - but I see several instances where people have the first sample occurring far past the edge of the flyback "edge". So by that time coil speed seems like irrelevant as the sample is occurring so far past the first valid data. We used beads on guitar amp inputs and had no visible or audible negative effects. High impedance inputs with similar gains.... just my first thoughts, no worries if I get shot down by theory or example...


Barry

[Coe42]

Mirror or not?

HI. I'M TURKISH. MY SURFMASTER PROJECT VER. 1.1

Hi Black, I 'm a little confused and I hope you can help me. I'm trying to transfer your schematics to a pcb using the toner transfer method. When I hit the 'print' button in the program (Sprint-layout) do I have to mirror the image that appears there or it is already mirrored?

Thank you!

[kt315]

the schematic you asked me for.

[Fred]

Hi Black, I 'm a little confused and I hope you can help me. I'm trying to transfer your schematics to a pcb using the toner transfer method. When I hit the 'print' button in the program (Sprint-layout) do I have to mirror the image that appears there or it is already mirrored?

Thank you!

Hi,
I am not Black but i use Sprint layout, you don´t need to mirror (mirror mark unchecked).

[Coe42]

Thank you!

Thanks Fred!