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1  Using Arduino / Project Guidance / Re: What sensor do I need? on: Today at 03:32:20 am
A $3 laser diode is out of your range?
2  Using Arduino / Sensors / Re: Sensor for measuring length of an object flying by, and the speed of it. on: Today at 03:31:01 am
Agreed, as long as the speed isn't changing as it goes by.
3  Using Arduino / General Electronics / Re: First benchtop oscilloscope, what specs matter? on: September 19, 2014, 10:23:01 pm
Agreed, my thoughts exactly.
4  Using Arduino / General Electronics / Re: First benchtop oscilloscope, what specs matter? on: September 19, 2014, 10:04:56 pm
Good points about sample rate vs number of channels active. I'm aware of that, but not everyone reading this thread know this. That four channel captures at 2Gsps combined, so with one channel, 2Gsps, two channels mean 1Gsps per channel, four channels 500Msps per channel.
5  Using Arduino / Project Guidance / Re: Putting a display on MAX038 on: September 19, 2014, 10:02:00 pm
If it is wired correctly, then it must be a defective chip.
6  Using Arduino / Sensors / Re: 0 - 10 V on: September 19, 2014, 05:41:21 pm
FYI for other readers, a 0-10V transmitter is simply a sensor of some kind that scales its output from 0 to 10V analog.

Yes, absolutely you can just wire up a voltage divider. 3.3V is just about exactly 1/3 of 10V, so something like  a 10k and a 4.7k will divide 10V down to 10*4.7k/(4.7k+10k) =  3.20V. Then just call the digital number you get from that full scale.
7  Using Arduino / Sensors / Re: Non-contact liquid sensors on: September 19, 2014, 05:37:26 pm
Capsense does just that, with the provision that you have a resistor on one pin and the capacitance being sensed is on another. Nothing but one resistor and two pins required.

8  Using Arduino / Project Guidance / Re: avoiding delay on: September 19, 2014, 05:35:44 pm
Yay!
9  Using Arduino / General Electronics / Re: Would this work? on: September 19, 2014, 05:34:27 pm
MarkT is correct! I missed that. The H11AA11 requires a diode connected antiparallel to its LED. Antiparallel means parallel, but pointing the opposite direction.

However, then you get a single pulse only when the AC is positive polarity. A more useful way is to use a bridge rectifier at the input (LED side) of the H11AA11. In that way, the phototransistor is nearly always ON, only OFF when the AC waveform passes through zero volts, whether it is positive or negative going at the time.

As far as the input to the MOC3020, it doesn't matter if you pull it low or high, as long as it is wired so current goes the proper direction.

OK, back to the 330 ohm resistor circled- it is there to make sure that random noise picked up by the wiring, stray leakage currents, that sort of thing don't inadvertently trigger the Triac when the MOC3020 is off.
10  Using Arduino / Motors, Mechanics, and Power / Re: Reading DC rms/average voltage from a pwm signal on: September 19, 2014, 05:24:57 pm
vffgaston is right, power is not proportional to voltage. Hence all my futzing about to calculate RMS voltage.

But the original poster has still not told us if he's figured out yet if he means RMS voltage, or average voltage.
11  Using Arduino / Motors, Mechanics, and Power / Re: Reading DC rms/average voltage from a pwm signal on: September 19, 2014, 05:23:26 pm
The Arduino pin should be a symmetrical drive, and so should not be a problem.

I have seen people here try to generate something like a 0-10Vdc signal by using a high side PNP switch with an RC network after to smooth it out. It never quite works because of the effects of assymetrical drive currents.

If it is the output of an H-bridge, that should also work as it is a symmetrical drive.
12  Using Arduino / General Electronics / Re: "power" drop when trying to control solenoid? on: September 19, 2014, 11:21:39 am
First, can you send us a link to the datasheet for the IR sensor? Is it an IR phototransistor, or a remote control receiver module?

Schematic of how it is connected when it lights the LED.
13  Using Arduino / General Electronics / Re: 'Reading' PWM duty cycle on: September 19, 2014, 09:00:09 am
Quote
Feed the output of the comparator into a diode and from there into a capacitor and then to GND. You'll have to play around with the capacitor values until you find the right one. With the right capacitor the voltage at the junction between the diode and capacitor will be proportional to the PWM duty cycle.

This is incorrect. The diode only sources current, so the capacitor simply charges to the peaks. If you have enough of a resistance discharging it and low enough capacitance, then you are still left with a huge ripple voltage and it still isn't the average voltage.

I answered a similar question here:
http://forum.arduino.cc/index.php?topic=267459.msg1888121#msg1888121

Quote
Or...because you've got a microcontroller you can totally skip the analog part and just count how long it's HIGH and how long it's LOW. You're looking at relatively low frequency signals so it should be quite accurate. Just put a 22K resistor between the PWM signal and the Arduino pin, job done.

I agree with that. That does seem to be what the OP is trying to do, but he's doing it in a way that is holding up the rest of the program.
14  Using Arduino / General Electronics / Re: "power" drop when trying to control solenoid? on: September 19, 2014, 08:54:02 am
So it works with the Arduino driving the transistor, but not with the IR receiver driving it directly.

That is not surprising. Most IR receivers are active low, and sink current. They are an open collector output. The transistor needs something that sources current.

So you'd need something to invert the signal between the IR detector and the TIP102. Like the Arduino.

Are you wanting to drive the solenoid directly from the IR receiver, or are you just curious and trying things out?
15  Using Arduino / General Electronics / Re: Battery Monitoring System for Arduino on: September 19, 2014, 08:50:29 am
Using lower resistance in the voltage divider will -not- damage an analog input, because that current is not flowing through the analog input.

Perhaps you meant that lower resistances provide less -protection- of the analog input in case of malfunction. That is true.
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