AVR+DSS Frequency Mod SD2100V2

[sido]

Hi Mario, the frequency mod with crystal's is documented by Ismael Jones for your reference. It will give you pin location to be able to tap into. There is also full circuit diagram available there after sign up. Do a search here also for (SD2000 circuit), it is available.

http://www.minelabmods.com/joomla/in...id=2&Itemid=40

If i get some time in couple of days, will look into it....Hope that helps

Sido

[IBGold]

Hi Mario,
The SD2000 will run directly with crystals from 1.25MHz to over 4.0MHz I even have a 6.0 MHz one in but I only use one channel when using it I have not try-ed lower crystals as they are too hard to get in Australia but my outboard VCO that I use runs from .985 MHz to 4.95 MHz and the detector will run all through that range no worries the problem with the VCO is it has slight jitter which degrades its performance the SD2000 has a jumper between the crystals fitted so that one or the other crystal can be selected this is where I feed the VCO signal and the six position crystal switch and where your signal would be fed into the unit.
Sounds like the SD2000 is much easier than the SD2100 to do but keep up the good work.

Regards, Ian.

[mario]

BoM

Parts list found here: BoM

Notice it's a work in progress. I will likely add more components, as I resolve the few remaining issues.

[mario]

Hi guys,

The signal has to be pure. The smallest jitter will cause so much noise,that it will render the detector unusable. However, after experimenting with my mod, I was able to get a very pure sine wave using a 100Mhz crystal. The audio is crystal clear as stock (kudos to Analog Devises for creating such a remarkable chip).

I pretty much have solved most of the issues. All heating problems disappeared after replacing the cheap Chinese regulator I bought from ebay.

The only issue that remains has to do with the indirect control of the frequency.

It seems that the stock VCO outputs a 50-60Khz frequency at pin 3. The VCO feeds the two caps which rev up the frequency to 1.2Mhz.And after shorting both caps, and feeding a 1.2Mhz signal, I lose audio.

It seems the only way to rev up the frequency involves removing the stock VCO and feeding those caps with a +50Khz signal.

I have a question to you SD2000 owners: are your detectors the same? Meaning, replacing those caps increases the frequency? If so, I'm not sure this mod will work on your detectors. It seems like I can indirectly control the frequency by having my mod exert a +50Khz to pin 3 instead of feeding a pure 1.2Mhz signal.

Or does your detectors tolerate a direct 1.5-4Mhz signal? I believe Jiminy mentioned something about having 1.5-4Mhz crystals, meaning a pure 1.5-4Mhz signal but I would like to confirm.

[gef12]

Hi Mario
Put me down for 2 mate... pm me when all is ready
tks for now
Geoff

[IBGold]

Mario please put me down for two also I will also start looking for components to suit.

Regards, Ian.

[mario]

I'm still working out the kinks.

This AD9851 operates warmer than I expected and was able to cool it down by disabling an internal 6x multiplier. Unfortunately, I won't achieve higher than 15Mhz frequencies with our 30Mhz crystal OSC, but the difference in thermals is baffling. For our purposes a 15Mhz max is more than enough since these parts will never exceed 4Mhz. I don't see anyway of accommodating a heat sink.

I would like to eventually experiment with a 180Mhz crystal OSC, but the cost is too prohibitive. These chips do shine at higher speeds though...

Anyway, I'm really happy with the lower thermals...The problem I'm now currently having involves the regulator. At a 6.2 volts input it runs cool. At 7.4 it runs warmer than I would like. I'm going to experiment with a different package and/or regulator. Once I get that solved, I will finally do some field tests.

I'll have to make a BoM soon, that way people may start ordering parts....By the way, the only parts not shown in the schematic involve power supply and low-pass filter -which is very different from the one used by the AD9851 datasheets.

The software is now mainly done. I just need some code in case people use the same board to experiment with SD2000s and SD2100s. Some parameters are saved and reused. People might unknowingly damage their SD2100s if I don't include some behind-the-scenes protective mechanism.

Anyways, I won't be able to do those field tests until I get those regulators.

I want to make sure this mod works well (these detectors are not cheap, and I want to take all the necessary precautions from damaging them).

[Jiminy]

Mario,
When you get ready to sell, I'll take two. Pls PM me with the details.
Is there a preferred parts list other than what is shown on the schematic?
Specifically which encoder did you use?
/r
j

[mario]

Hi, Jiminy

I've rewritten the program to include software compatibility for the SD2000s.

Currently, to switch between modes, you'll have to toggle pin 27 (ground it for 1/3 of a second). I didn't think providing two separate binaries was necessary considering I could include support in the same program.

"SD2000 Mode" will give you access to the higher frequencies and scale the frequency steps better. To switch back to "SD2100 Mode," just toggle pin 27 again.

So far I'm still testing the unit. I would like to assemble another unit to solder up to my case, but need to order another AD9851.

Unless I find any other issues with the boards, I'll probably end up selling them for $10. I will only have 7 up for sale and will not make them again. If I do sell out and anyone wants one, that person may create a working unit from my posted schematic. I made several changes from my original prototype and will update it some time in the near future.

Now, regarding my power supply.

My lipo pack is rated at 8AH 11.2V. However, fully charged this thing gives me a constant 12Vs. Unfortunately, because I have to step down the voltage to 7.4V, the regulator gets hot. 12V->7.4V drop is a huge difference.

I have literately gone for days with out charging (while detecting 6-8hr/day), but I would discourage people from using such a set up. Other than needing a heavy duty regulator, you really want to avoid such a set up because of noise issues. Running the current through the regulator introduces noise to the system. So you want to draw your power from the source as directly as possible.

One of the Mods I'm considering involves digitizing the signal using a 20bit ADC. I have thought about feeding the signal to a UC3 (32bit AVR) chip for processing. However, because of the current noise issues, I will be lucky if I get 10 bits.

I will definitely need to clean up the system if I ever implement that mod.

[Jiminy]

Mario,
Board looking good. Looks like you have quite a power supply box there. That LiPo board, is that the one from MicroChip? I have one. Plan to use it to make a MD power supply also.

I have a Willem programmer that should suffice in programming the AVR as well as the 27C256.

Keep us posted.
/r
j

[Jiminy]

IBGold,
Yes, I received the information you sent. I've been out of state for the last two weeks and getting caught up in the office. Hope to start chasing voltages on the 2000 this weekend. Appreciate your assistance. /r J

[mario]

Sorry about the broken html code linking the video. I'm not sure how to get it working, so you may view the video here: link

To program the board, you will need a programmer. You can build your own using the schematic found here with this software: pony prog. Otherwise, you may purchase one of the many AVR ISP programmers found on ebay. Just make sure you find one with a 10 pin ISP header.

[mario]

got it working

<iframe width="425" height="349" src="http://www.youtube.com/embed/jfPPs3EW6jo?hl=en&fs=1" frameborder="0" allowfullscreen></iframe>

I finally assembled my board.

With the exception of a minor error on the lay out (on the first pic, you can see a yellow wire jumping the wiper of a var resistor to a nearby component), the board works as intended!

I had a hard time soldering the AD9851 IC - I'm no fan of SSOP, but I didn't have any issues aligning pins. I will highly recommend a brand new soldering tip and lots of flux.

I like my modular design. I can now cut a separate AD9851 daughter board to fit inside the case to better cope with size constraints. I'm currently thinking about placing the main controller board inside my power unit (you can view that here). But, I'll likely create a separate control panel if i'm able to accomodate the whole board inside the case.




I haven't finished testing it. Nor have I written code for the higher frequencies used by the SD2ks. And unfortunately, I'm very time constrained...

[IBGold]

Hi Mario,

Sounds good keep us informed I would like to see it capable of having from 1MHz to 4MHz capability for obvious reasons.
Jiminy did you receive the information?.

Regards, Ian.

[mario]

Hi Jiminy,

I am also excited about bringing this project to completion. I have been working months on this little board, and I'm looking forward to resuming my prospecting.

If all goes well I will hit those gold fields some time next week.

I have thought about my next project, considering that there maybe a way to reprogram that eeprom without removing it- you have to replace it initially with a reprogramable part of course, but once you have done it, it may be a simple matter of soldering some wires from my board and have the atmega flash it.

Still, I don't know if it may be worth it considering that we have not made our custom timings yet, so I'm leaning towards something else.

I don't want to say anything just yet, but it may be something most md users , not just us minelab guys, will benefit...

ill update you next time I have made some progress...