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Topic: Your latest purchase (Read 121648 times) previous topic - next topic

liudr

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.

Chagrin

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.


Constantin


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.

cyclegadget

Quote
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.
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

GoForSmoke

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

https://www.youtube.com/watch?v=aOJuCYgmPPE
Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

cyclegadget


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.
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

Constantin

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.

cyclegadget

Quote
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.
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

Nick Gammon

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. :)
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

GoForSmoke

I look forward to articles on timing at 20 MHz.  :D

Nick Gammon on multitasking Arduinos:
1) http://gammon.com.au/blink
2) http://gammon.com.au/serial
3) http://gammon.com.au/interrupts

retrolefty

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

Nick Gammon

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!
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

Nick Gammon

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.
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

Coding Badly

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.

Coding Badly

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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