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[Reply #465 on:]

After having to wait for restock notification before ordering I was finally able to get a couple of items from ADAfruit that looked especially interesting to me. They arrived yesterday and both products get a lefty's thumbs up report.

First is an assembled (minus soldering on stacking headers) SD/RTC shield board for just $20. This thing is sweet, worked right off the bat and has good library support for both the SD and RTC. Everything functioned using the example sketches, although you do have to edit some SD sketches to utilize pin 10 for SS function as several are set up for a ethernet board that uses pin 4 for the SS. They include the back up battery for the RTC. The board has a two uncommited led/resistor networks for one's use and the board has it's own 3.3 vdc regulator to power the SD, it duplicates the pin13 led on board. It has a system reset switch, but does not have dedicated ICSP 2x3 pin headers. They use a real voltage translation chip rather then voltage dividers for the SD logic to arduino voltage conversion. Anyway great price, great quality, good library support, what more could one want for the basics for logging applications?

http://www.adafruit.com/products/1141

Second item is a $10 4 channel (or 2 channel differnial) 12 bit I2C ADC chip/module based on the TI ADS1015 chip. This cool chip has built in internal voltage reference, 6 different gain settings, voltage comparator with output pin, and many other features and functions. It's a great little chip that does a lot. Adafruit has a library that supports the chip and I had no trouble getting it to function. Maybe not really needed with the arduino having built in 10 bit ADC pins, but I just felt that the SD/RTC data logging shield was just begging for the extra precision and features this little ADC module would bring to the party. They also carry the same module equipped with the 16 bit ADC version of the chip called the TI ADS1115, for $15. So I just soldered a 10 pin male header onto the SD/RTC board and soldered a 10 pin stacking header on the ADC module so the module can live on the SD/RTC shield or be easily unplugged and used elsewhere if needed.

12 bit ADC   http://www.adafruit.com/products/1083

16 bit ADC   http://www.adafruit.com/products/1085

Well that's the report of the latest. Adafruit is great at Arduino support and makes and documents well a lot of very cool and useful stuff, check them out if you haven't already.

http://www.adafruit.com/

Lefty

[Reply #466 on:]

Well I didn't buy it myself, but look what I got from the Fluke Fairy for Christmas.... They were out of stock and it arrived last week 

[Reply #467 on:]

Lefty,

Nice chips/breakout boards. I'm still looking for easy to use bipolar ADC to measure +-10V range. Too bad these ones are unipolar.

[Reply #468 on:]

This is an MCP3422 (16 bit, 2 channel differential, 0-7V, I2C) on one of dipmicro's adapters. Somehow I soldered this one OK but don't think I'll buy these adapters again. You'll have to forgive me for going pretty light on the solder on those pin headers.

[Reply #469 on:]

Nice chips/breakout boards. I'm still looking for easy to use bipolar ADC to measure +-10V range. Too bad these ones are unipolar.

May I suggest the use of a custom-made  ADC driver chip from Analog Devices for this purpose? The 8275 will not only take that bipolar input and reduce the output to 0-4VDC, it'll also create a nice signal centered around 2VDC, perfect for differential ADCs with unipolar inputs.

[Reply #470 on:]

May I suggest the use of a custom-made  ADC driver chip from Analog Devices for this purpose? The 8275 will not only take that bipolar input and reduce the output to 0-4VDC, it'll also create a nice signal centered around 2VDC, perfect for differential ADCs with unipolar inputs.

 Do you think that chip would work with a guitar? My guitar outputs .7volts AC rms . I need a high impedance amplifier to make the guitar signal compatible with the Due input. I would like the level centered at 1.5V with about 1.5V swing.

[Reply #471 on:]

There's a DIY pre-amp circuit shown on this short youtube. Maybe it will help?

https://www.youtube.com/watch?v=aOJuCYgmPPE

[Reply #472 on:]

There's a DIY pre-amp circuit shown on this short youtube. Maybe it will help?

https://www.youtube.com/watch?v=aOJuCYgmPPE

Thank you,
 I think that circuit will only work for a piezo but, it put me on a better track for finding a circuit design. After following your link, I found some other sites that have some ideas that may work.

[Reply #473 on:]

Cyclegadet,

I suggest you take a look at the Analog Devices and TI web sites. Both offer a wealth of information re: op-amps and from the looks of it, your application is tailor-made for an op-amp. You could go for a G=1.5 circuit that simply shifts the signal from +/- 0.7Vrms to 1.5VDC +/- 1.5Vpp. That would result in a signal from 0-3VDC, well within the specs of the Due ADC. Plus, you gain the benefit of a low-impedance source, i.e. one that will make the ADC inside the Due very very happy.

[Reply #474 on:]

You could go for a G=1.5 circuit

 That is so simple! Why didn't I think of that?!!!  That could very well work. I will double check my voltages from the guitar and then try your idea.

[Reply #475 on:]

100 x 20 MHz crystals ... for $3 from eBay.



Now I'm going to try running at that speed. Although to be honest, they sound unbelievably cheap.

[Reply #476 on:]

I look forward to articles on timing at 20 MHz. 

[Reply #477 on:]

That is dirt cheap. Tayda has them for .10 each which I thought was awful cheap.

http://www.taydaelectronics.com/crystals-resonators-oscilliators/20-000-mhz-20-mhz-crystal-hc-49-s-low-profile.html

Should be a pretty simple hack in arduino, recompile bootloader fro 20Mhz and make new modified entry into core's boards.txt file. Anything else I forgot?

Lefty

[Reply #478 on:]

Just for fun I programmed via the ICSP interface with the ASCII table sketch, set to output at 9600 baud.

At 20 MHz it output (seemingly correctly) at 12000 baud which sounds right (9600 * 20 / 16 = 1200).

Then I put in one of the 24 MHz crystals that I also ordered (because dhenry claimed you could clock it at 24 MHz) and it output at 14400 baud (9600 * 24 / 16 = 14400). So on the face of it, you can run at higher speeds. Now I can't say for sure that it is working perfectly, but after running for 10 minutes or so, the ASCII table is still coming out.

Trap for young players: I initially saw no output, which I spent 15 minutes mucking around trying to fix, until I realized the sketch only outputs the table once. At 24 MHz that doesn't take long!

[Reply #479 on:]

He still seems to have them for $3:

http://www.ebay.com.au/itm/100pcs-20-000MHZ-20-MHZ-20M-HZ-DIP-Crystal-Oscillator-HC-49S-New-/190767216545?pt=AU_B_I_Electrical_Test_Equipment&hash=item2c6a9cb7a1

Now I can't say they are all working. But one I picked at random did.