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Author Topic: Your latest purchase  (Read 99353 times)
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Central MN, USA
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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.
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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.



* MCP3422_on_breakout.jpg (81.95 KB, 640x513 - viewed 34 times.)
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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.
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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.
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There's a DIY pre-amp circuit shown on this short youtube. Maybe it will help?

https://www.youtube.com/watch?v=aOJuCYgmPPE
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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.
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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.
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You could go for a G=1.5 circuit

 That is so simple! Why didn't I think of that?!!!  smiley-eek That could very well work. I will double check my voltages from the guitar and then try your idea.
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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. smiley
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I look forward to articles on timing at 20 MHz.  smiley-grin

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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
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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!
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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.
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Anything else I forgot?

millis and its ilk will be off.

This... http://arduino.cc/forum/index.php?topic=70475.0 ...cures millis (for 20 MHz).

I can probably rustle up a fix for micros (which fixes delay) if you need it.  For delayMicroseconds I suggest using _delay_us from AVR Libc.
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Now I can't say for sure that it is working perfectly...

I vaguely recall from the folks at avrfreaks that EEPROM writing is the first to "go" as the clock speed increases.
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