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Now I have another question, could the Axon's 5V supply power the circuit instead of using a 9V battery + the 5V voltage regulator?
Yeap, up to 1.5A, assuming the chips you use work at 5V.If you do, put various caps before and after the voltage regulator until an oscope says the signal is clean.
You're amplifying tiny signals, so noise gets majorly amp'ed too . . .
Quote from: Admin on July 07, 2009, 11:28:51 AMYeap, up to 1.5A, assuming the chips you use work at 5V.If you do, put various caps before and after the voltage regulator until an oscope says the signal is clean. I'm not sure what you mean here. I was thinking I could connect the 5V from the axon to the circuit in the same manner as my current 5V voltage regulator's output pin does. Is this not the case?
Quote from: Ocelot on July 07, 2009, 12:02:35 PMQuote from: Admin on July 07, 2009, 11:28:51 AMYeap, up to 1.5A, assuming the chips you use work at 5V.If you do, put various caps before and after the voltage regulator until an oscope says the signal is clean. I'm not sure what you mean here. I was thinking I could connect the 5V from the axon to the circuit in the same manner as my current 5V voltage regulator's output pin does. Is this not the case?This is true, however the Axon isn't designed for high signal amplification. You need to make sure your power supply is ultra clean (in your schematic, your power supply has zero buffering - bad!). You can do this simply by adding caps before and after the regulator until its as clean as you require. I only made it clean enough to get decent 16 bit resolution from a battery.
Ok that makes sense now, thanks! What range of capacitor values should I work with to accomplish this?
Quote from: Ocelot on July 07, 2009, 12:57:55 PMOk that makes sense now, thanks! What range of capacitor values should I work with to accomplish this?Depends entirely on the frequency of the noise(s). Knowing nothing about your system, I'd do a .1uF, 1uF, and 10uF rated at 10V+ on both halves of the regulator, then look at the signal real close with an oscope. Tantelum type cap is best, but ceramic ok.
If I'm using the Axon 5V supply, why would I need to include the 5V regulator at all in my circuitry? Then I'd only need a capacitor between the Axon 5V supply and the rest of the circuitry (virtual ground+diff amp+rectifier), right?
For EMG work, I wouldn't rely (solely) on an integrated regulator, as they're way too noisy, however you cap them.At least follow the regulator by a gyrator circuit (which can easily drop noise and hum [yes, hum can get radiated into a battery supply too] on the supply by a further 80..90 dB for a modest outlay). A CLC-filter wouldn't go amiss either.The cleaned up power rails should be kept well away from any digital circuitry.
When connecting an EMG amplifier to a controller, it's very important to lay out the analog and digital grounds correctly and have only one common point.
The amplifier need to be in a shielded metal box (µmetal is über here, copper would do, but choosing between alu and iron would depend on which kind of noise source, E or H is the major) and by shielded, I mean with a labyrinth for the power leads and feed through caps for signals.
Twisted input leads is very important to get the common mode noise down, experiment with the tightness of the twist, that depends on the major frequency band of the noise.