HH2 -- Take Two

[Carl-NC]

I haven't been able to work on this much lately, but I did make a few mods to the schematic & PCB. The biggest change is the move to a 2-stage preamp. I also added a trace on the PCB so the preamp can directly drive the ADC in the micro. You could then experiment with software integration/averaging. The PIC ADC is only 10 bits, but I have tried it and got surprisingly decent results. Good enough for an experimental platform, anyway.

Following is a 150dpi GIF schematic.

- Carl

[Carl-NC]

Here is the PCB...

[Carl-NC]

Here are higher-res PDFs. The PCB file is at 2x actual size.

[Carl-NC]

The next step is some PIC code. I will try to get to this ASAP. I have done quite a bit of it already but in another processor, so I mainly need to pull the code over to the 12F and make sure it works.

I may decide to make a small batch (25-50) of PCBs after all. If I do, I will sell them but with a limit of 1 per person.

- Carl

[Altra]

Carl,
Nice design! Your selection of the MAX412 for the pre-amp, sparked my interest. Not being familiar with this part, I went to the maxim web site to get the data sheet and this part is being discontinued. There are parts still available from them and some of the supply houses. Is there a specific reason this part was selected? I noticed it has a 1.3uS settling time.

Something you might want to add is pads for a trimpot between the pic12f683 power rails and the wiper to the ADC pin. This can be used to adjust your sample delay. The adc results can be scaled and then added or subtracted from the sample delay loop in the software. It works good in most cases. This would make it more adaptive to different coils with out having to reprogram fixed delays for each situation. Put me down for a PCB if get some made.

Thanks

Mark

[DEMAC]

MAX412 REPLACEMENT

HI,CARL

IS POSSIBLE TO REPLACE MAX 412? ARE THERE OPTIONS?

IS CLOSE TO IMPOSSIBLE TO FIND AROUND HERE

THANKS SO MUCH

[Carl-NC]

I originally thought about putting in adjustable pulse width, sample delay, sample width, etc just like HH1 has. I decided against it for this version because I wanted to focus on the basics of using a microcontroller, i.e., keep it simple. However, the sample delay really is a valuable adjustment, so I may reconsider. There is no room for a trim pot so I may be limited to adding solder pads.

The MAX412 was chosen because I've found it to be one of the best for PI preamps. I think only the MAX414 (quad version) is being discontinued, and probably because it's a 2-chip hybrid. The MAX410 & 412 are extremely popular opamps and shoud be around for a long time. Yes, you can use other opamps; any wideband in a standard dual pinout (NE5532, etc).

- Carl

[Altra]

Carl thanks for the response. I was thinking no need to modify the PCB. You could just make a small piggy back pcb to match what ever micocontroller and extras you want to use. This keeps it simple. I think I'll order some of the MAX410s and 12s.

Mark

[Carl-NC]

The next post has the latest schematic and PCB image. I added pads for a pot that can be used to provide one user-adjustment, such as sample1 delay. This has to go to one of the ADC pins and there were no free pins, so I added CT pads to both the 'N8' and 'ADC' lines. For any given option they are unlikely to both be used for their intended function.

Adding a pot control is a Good Idea because this design is intended as a tutorial in micro programming, and it's something I should cover. A larger PIC could be used to offer more control pots, and the coding will be the same.

- Carl

P.S.-- New pads required rewiring the PIC to make 'N8' an ADC-capable pin. Also, the circuitry for N8 was from HH1revD which is incorrect for the PIC, so I changed it.

[Carl-NC]

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[Carl-NC]

I finally ordered PCBs for HH2... should see them in 3-4 weeks.

[bbsailor]

I finally ordered PCBs for HH2... should see them in 3-4 weeks.

Carl,

Please reserve one board for me. Also, please advise how and where to send payment?

bbsailor

[Carl-NC]

As soon as I test one I will post info on ordering. Same deal as before, $10 shipped. I will have to limit it to one per person as I only made a batch of 50.

[Ray-NM]

I will take one.

i will take one Carl.
RayNM

[WM6]

Excellent pcb. Must have one.