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 16 Using Arduino / Project Guidance / Re: Blocking -VDC on: April 17, 2014, 09:42:33 pm Ok, I've just never seen that configuration used. Funny how many words it takes to describe what a simple schematic drawing might make obvious.
 17 Using Arduino / Project Guidance / Re: Ground-side switch output? on: April 17, 2014, 03:37:20 pm Might need a more detailed example of what you need, but standard arduino output pins can both source (when HIGH) and sink (when low) current, but with a current limit of 40 milliamps absolute maximum. If higher current is required then additional output components are required, like mosfet switching transistors that can be configured for high or low side switching.
 18 Using Arduino / Project Guidance / Re: Blocking -VDC on: April 17, 2014, 03:28:26 pm Quote from: polymorph on April 17, 2014, 01:48:28 pmJust commenting on the idea of using a motor as a generator to determine direction:Connect one terminal of the motor to a voltage divider at Vcc/2. Connect the other, through the appropriate resistors and diodes to protect the Arduino and capacitor to smooth the signal, to an Analog input pin.Motor spins one way, voltage>2.5V. Motor spins the other way, voltage<2.5V. You could connect a second Analog input to the voltage divider to get an accurate read of zero speed voltage.Load the motor down with the right resistor across it, and you can probably get a reasonable indication of speed, too. The resistor should go right across the motor. That doesn't sound right to me. A DC generator to turn in both directions must cause the voltage to change polarity, so voltage output of your 'simple method' would be some positive voltage in one direction depending on speed, and the same voltage but negative if driven in the opposite direction at the same speed. And as arduino analog inputs can not measure negative voltages, how could it work?
 19 Using Arduino / Audio / Re: Small Class D amplifier on: April 17, 2014, 03:12:41 pm Quote from: permnoob on April 17, 2014, 03:02:12 pmwow that's a lot of sources quick, thanks guys!  I'll take a look at em now.  @retrolefty and DVDdoug:  I meant put the speakers in parallel, not the amps, so I can drive more power at the same voltage.  However since class D amps are 'digital' I figure they are a bit harder to predict how they will behave outside of thier rated range of loads compared to AB amps.  Gotta dig into the datasheets to konw for sure.  stupid low voltage supply, BUT since it is so close to automotive range, I know there must be devices out there specifically for it. Well keep in mind that 'digital' class D amps are still analog as seen by the speaker loads as there is a low pass filter output stage on any audio class D amp. Also halving the speaker impedance does not automatically double the output power unless the amp is rated for the increased current demand for the decreased speaker impedance. The datasheet for the amp chips should always be studied to determine what actual power output you can get at a give device voltage and speaker impedance. There is more to it then simply ohm's law.
 20 Using Arduino / Project Guidance / Re: Arduino Nano as USB HID on: April 17, 2014, 02:59:50 pm Not possible with a Nano as it uses the special purpose FTDI chip to perform the USB serial interface, not a programmable AVR chip such as the 16U2 chip the standard Uno board uses.
 21 Using Arduino / Audio / Re: Small Class D amplifier on: April 17, 2014, 02:41:06 pm Quote from: DVDdoug on April 17, 2014, 01:19:46 pmQuote i am hoping I can put several in parallel to dropthe eff resistance to whatever the minimum the amp can handleA Bad, bad, bad, idea!    The general rule is NEVER connect outputs together. (That's why you use an audio mixer to mix audio signals.)   Solid state amplifiers have very low internal source impedance (often less than one Ohm).   The output of one amp "shorts out" the output of the other.The most common "trick" is to make a bridge amplifier.    That doubles your peak-to-peak output voltage (theoretically 26V P-P = 9V RMS) with a 13V power supply) and that gives you 4 times the power into the same load.  Doubling the voltage doubles the current, so an 8-Ohm speaker "looks like" a 4-Ohm speaker to each amplifier.   In theory you can get about 10W into 8 Ohms, but there is some voltage drop across the transistor/MOSFET and you can't actually get the full power supply voltage across the speaker.High power automotive amplifiers have a voltage-boosting power supply. And for 'bridging' to work the audio signal input must be inverted 180 degrees in one of the amps.