Show Posts
Pages: 1 2 [3] 4 5 ... 440
31  Using Arduino / Project Guidance / Re: Controlling Turbocharger Solenoid With Arduino on: January 02, 2014, 03:32:04 am
1. Your "voltage divider" fed from S1 is not a voltage divider, it is a  22K pulldown resistor follows by a 47K series resistor. It will work, however it would be better to use a 47K resistor between the voltage source and the pin, and a 33K resistor from the pin to ground. Same for Vss and Ford PCM inputs if they are also 14V signals. The 47K is large enough to protect the inputs from at least 50V transients. If you want more protection than that, use 100K and 68K instead.

2. I would use 10K in series with the analog inputs, not 1K.

3. I would add a 100 ohm resistor in series with the mosfet gate.
32  Using Arduino / Project Guidance / Re: New project to automate a rotary drum filter for a fish pond on: January 01, 2014, 07:24:59 am
Personally I wouldn't use a relay, however If you only need to run the motor one way, then a mosfet + flyback diode will do the job for a lot less money than a motor shield.
33  Using Arduino / Project Guidance / Re: New project to automate a rotary drum filter for a fish pond on: January 01, 2014, 06:50:36 am
The first one is no good for your application, but the second one looks like a good choice to me.
34  Using Arduino / Project Guidance / Re: Protecting Arduino inputs from external inputs on: January 01, 2014, 04:47:20 am
I build lots of these testing modules if you will and on average I have to feed 0.94 volts for the Arduino to read 0.90 volts.  Some Arduinos require 0.94, some 0.95 and the highest I've had is 0.96 volts.  However going through the op amp I see I have to feed it 1.04 volts to for the Arduino to register 0.90 volts.   I know op amps can do scaling and its got me thinking am I inadvertently scaling the voltage without meaning to?  How do I correct this difference?  I need the Arduino to correctly read the voltage for my projects.

Your two main sources of error will be:

1. The analog reference voltage you are using. Don't use the default 5V reference if you will be powering the Arduino from USB or from an external 5V supply, because it will not be stable enough to provide a good reference. You can use the 3.3V pin as analog reference, which is more stable but will still vary a little between Arduinos. If the voltage you need to measure doesn't exceed 1V (or knowing "input above 1V" is sufficient when it does), then you can use the internal 1.1V reference, but again it will vary a little between Arduinos. I suggest you can store a calibration constant in the Arduino EEPROM.

2. The input offset voltage of the op amp. See its datasheet for how big this can be.
35  Using Arduino / Project Guidance / Re: New project to automate a rotary drum filter for a fish pond on: December 31, 2013, 04:33:47 pm
The standard Arduino motor shields use very old technology and are quite pathetic in their current handling capacity. Check whether the one you plan to use is adequate to drive your motor and solenoid before designing them in.

To adjust the set points, consider using a rotary encoder, with or without built-in push button.
36  Using Arduino / Project Guidance / Re: Arduino quadcopter pilot - electronics questions on: December 31, 2013, 12:20:20 pm
If you must do it yourself, here are some suggestions:

1. Run the Arduino at 3.7V, not 5V. You can't afford the weight of a boost converter. In fact, it if is a small quadcopter, it won't be able to carry the weight of a full Arduino board anyway. So prototype it on an Arduino, then migrate it to a bare-bones design when you have it all working.

2. TIP120s are rubbish for this application because of their saturation voltage. Instead, pick a small mosfet that needs only 3.5V gate voltage to switch it fully on. You must be building a small copter if you are not using ESCs, so you had better use SMD mosfets to keep the weight down. Maybe TSM2314CX.
37  Using Arduino / Project Guidance / Re: Usage of Arduino DUE for high speed data aquisition on: December 31, 2013, 12:11:46 pm
Even an ordinary 8-bit AVR Arduino could do that, it doesn't need a Due unless the analysis you speak of is very complex..
38  Using Arduino / Project Guidance / Re: Protecting Arduino inputs from external inputs on: December 31, 2013, 12:08:30 pm
Ahh didn't even know about that capacitor.  Will see what I can get added in there.  It's using the 5 volt power source from the Arduino.  I take it that's a noise supply?

Noise on the supply isn't the issue,the issue is that the op amp may be unstable without it. It's shown in Fig. 2 on the TI datasheet.
39  Using Arduino / Project Guidance / Re: Protecting Arduino inputs from external inputs on: December 31, 2013, 03:45:02 am
1. Make sure you have a decoupling capacitor across the power pins of the op amp. 0.1uF ceramic should be fine.

2. Try connecting a capacitor (0.1uF of 0.01uF) in parallel with the 47K feedback resistor.

3. Check your wiring.
40  Using Arduino / Sensors / Re: Why analog read value is fluctuating? on: December 30, 2013, 03:13:42 pm
If you are powering the Arduino from USB then the biggest source of error may well be fluctuations in the voltage of the +5V supply while the reading is being processed by the ADC. For more accurate results, connect the pot between +3.3V and ground, and also use +3.3V as the analog reference. Read the precautions for using an external analog reference before doing this.
41  Using Arduino / General Electronics / Re: Help with some electronics math... on: December 30, 2013, 05:54:40 am
I suspect that if you follow the traces, you will find that all 3 pairs of terminals connected together. However, even if this is the case, the terminals themselves and their connections to the PCB may not be rated for 20A, so you should run 3 sets of wires between the PSU and your load even if you are not splitting it.
42  Using Arduino / Project Guidance / Re: Controlling Turbocharger Solenoid With Arduino on: December 28, 2013, 07:50:15 pm
See http://playground.arduino.cc/Main/TimerPWMCheatsheet. On the Uno, each timer controls a pair of pins. Leave timer 0 alone, otherwise you mess up the millis counter. For getting an analog output, increase the PWM frequency to maximum (31.372kHz), so use a PWM pin that is not on the same timer as the one you have reduced to 167Hz. Use a low-pass filter after the pin, e.g. 22K in series with the output pin feeding 0.1uF to ground; or 2.2K feeding 1uF, etc.
43  Using Arduino / Project Guidance / Re: Controlling Turbocharger Solenoid With Arduino on: December 28, 2013, 02:02:40 pm
You don't have to do the bit shifting yourself, if you divide an unsigned expression by a constant that is a power of 2, the compiler will do it for you.

0.5 is rather a high value to use in that code, it's hardly averaging at all. Something in the range 0.1 to 0.2 would give you an average over more samples.
44  Using Arduino / Project Guidance / Re: Controlling Turbocharger Solenoid With Arduino on: December 28, 2013, 11:38:52 am
The exponential average is simpler to compute (it doesn't need an array of past values), but really needs to use floating-point arithmetic, which is slow. The last-N-readings average can be done using integer arithmetic (although you may need to use a uint32_t aka 'unsigned long' variable to accumulate the total, depending on N), so should be faster. For most applications, I prefer to use the last-N-readings average. If you make N a power of 2 and use an unsigned variable to accumulate the total, then the division step will be implemented as a shift, which makes it faster,
45  Using Arduino / Project Guidance / Re: Generate Reference Signal 0.5 Vrms and 60 kHz using Arduino on: December 27, 2013, 04:54:10 pm
Sorry, I don't have a block diagram, just the schematic and firmware on github that I linked to.

If the equipment you are currently using uses a 40MHz signal, then I guess the capacitance you are measuring must be very small. What make you think that a much lower frequency such as 60kHz will work as well?

The easiest way to make a phase sensitive detector (aka lock-in amplifier) that works at ~40MHz may be to use a multiplier IC such as http://www.analog.com/static/imported-files/data_sheets/AD835.pdf.
Pages: 1 2 [3] 4 5 ... 440