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1066  Using Arduino / General Electronics / Re: identifying some components please on: October 16, 2013, 07:51:27 am
That is almost certainly the TX2B chip as a COB (chip on board) under the blob on the little circuitboard.

Scroll down to "4 Channel Transmitter":

Another page:

1067  Using Arduino / General Electronics / Re: Problem with 4N35 optocouplers on: October 15, 2013, 02:04:49 pm
Are these SMD resistors? If so, 220 means 22 and no zeros, so that's 22 ohms. For a surface mount resistor, 221 means 220 ohms.

Otherwise, it sounds like perhaps a short somewhere in the wiring?

What happens if you replace the optoisolators and resistors with visible LEDs and different resistors?
1068  Using Arduino / General Electronics / Re: Which Mosfet/transistor? (3V input) on: October 15, 2013, 02:01:09 pm
You have to be more specific than:

Then the + of my power source and the VIN of the Arduino to the remaining pins.

In any case, if you try to high-side switch power using an NPN transistor, the base must be able to go a few volts higher than the voltage you are trying to switch so as to overdrive the transistor to get a lower VCE, or it'll drop at least 0.6V, or more. The 2N2222 isn't that well suited to being a switching transistor.

A PNP transistor will make a decent high side switch. Overdriven, it should have only a few tens of mV dropped across the collector to emitter. But you'll need an NPN driven from the PIR output through a resistor, then the NPN collector pulls the base of the PNP low, also through a resistor.

Do you need a schematic?
1069  Using Arduino / Project Guidance / Re: Mosfet getting hot and motor vibrating using a 3.6v motor. on: October 15, 2013, 12:16:48 pm
The lower the gate voltage is to what is recommended, 10V, the hotter it gets.
Likewise if the gate is too far over the recommended voltage it will also get hot.
10 volts is the sweet spot.

Not true. See figures 1 and 2 in the datasheet given. 10V is merely the point of diminishing returns. 15VGS only gives you slightly lower RDS than 10VGS does.
1070  Using Arduino / General Electronics / Re: Emulating diode behavior with transistors on: October 15, 2013, 12:10:32 pm
A motor is not like a simple inductor. Are you sure that a diode is what you need in that circuit? Unlike an inductor, when you remove power from a PM DC motor, the freewheeling motor continues to generate voltage of the same polarity as the DC voltage that originally powered it.

And if you short the motor, it can cause -considerably- more current to flow than what it took to run the  motor at speed. The motor will also quit turning very quickly, this is called dynamic braking.
1071  Using Arduino / General Electronics / Re: 10 DACs - 1 Arduino on: October 15, 2013, 06:54:04 am
Using an Op Amp lowpass filter or even a two stage passive low pass is much better than a single RC lowpass.
1072  Using Arduino / General Electronics / Re: 10 DACs - 1 Arduino on: October 14, 2013, 06:21:44 pm
Have you considered using SPI devices? It'll take more pins, but it seems like it may be simpler. And if you are replacing potentiometers, would digital pots be a better choice? Depends on the resolution you need.
1073  Using Arduino / General Electronics / Re: 10 DACs - 1 Arduino on: October 14, 2013, 06:16:53 pm
Doh! Sydlexia ksirtes agian.

I see the Adafruit page says:
We break out the ADDR pin so you can connect two of these DACs on one I2C bus, just tie the ADDR pin of one high to keep it from conflicting.

When you tried using the PWM "analog" outputs, how did you filter it?
1074  Using Arduino / General Electronics / Re: DC to DC boost converter on: October 14, 2013, 05:57:42 pm
As pointed out, you can't just feed a supercapacitor with a stiff 24V. Rather, you want a constant current, or at least a current-limited charge, with a voltage limit of 24V.

As pointed out, however, multiplying the voltage to the output results in multiplied -current- to the input. So 500mA charge current at 24V would be 4A at 3V input. However, the switching upconverter chip will have peak currents much larger than that, 2 to 3x larger.
1075  Using Arduino / General Electronics / Re: 10 DACs - 1 Arduino on: October 14, 2013, 05:48:11 pm
The Due has 12 analog inputs. Or more correctly, a 12 channel analog switch to an ADC.

Do you mean that you need 10 separate ADCs? Can they not be switched, or do they all need to be synchronized for some reason?
1076  Using Arduino / General Electronics / Re: Extend Pulse from Op-Amp/Photodiode combo? on: October 14, 2013, 05:45:23 pm
Nicely done.
1077  Using Arduino / Sensors / Re: Long range RFID or other sensor on: October 14, 2013, 03:03:22 pm
You can add a directional antenna to that, too, which will boost the range and allow a direction measurement to be made. Animal tracking has been done that way for decades.
1078  Using Arduino / General Electronics / Re: Ambient radio wave energy on: October 14, 2013, 11:22:50 am
I demonstrated some of the effects of resonance by having an untuned coil connected to a signal generator, an untuned coil connected to a couple of antiparallel LEDs, then I insert an LC tuned circuit.
1079  Using Arduino / General Electronics / Re: RC522 (RFID) + mega 2560 - how can I use 2 RFID shields? on: October 14, 2013, 11:17:58 am
It is good policy when posting a question about specific hardware to post a link to where you bought it, or to a datasheet. Not for the Arduino itself, unless it is some unusual variant.

Here is Electrodragon's Arduino example code and connection:

I suspect it may be as simple as duplicating some code and changing the Select pin in the duplicated code. I see there is a Library for it. Looks like it uses SPI. For SPI, every device connects to the same 3 pins, plus a separate select line for each device.

From the SPI Library page:

With an SPI connection there is always one master device (usually a microcontroller) which controls the peripheral devices. Typically there are three lines common to all the devices:
MISO (Master In Slave Out) - The Slave line for sending data to the master,
MOSI (Master Out Slave In) - The Master line for sending data to the peripherals,
SCK (Serial Clock) - The clock pulses which synchronize data transmission generated by the master
and one line specific for every device:
SS (Slave Select) - the pin on each device that the master can use to enable and disable specific devices.
When a device's Slave Select pin is low, it communicates with the master. When it's high, it ignores the master. This allows you to have multiple SPI devices sharing the same MISO, MOSI, and CLK lines.

Someone with more Arduino experience that I will undoubtedly steer you more in the correct direction.

Posting links to the hardware information and what information you have, and efforts you've made so far, can let people know that you have tried to solve it on your own, first. But we do recognize that you must start somewhere, and often it is just a matter of not even knowing what to look for.

1080  Using Arduino / General Electronics / Re: Extend Pulse from Op-Amp/Photodiode combo? on: October 14, 2013, 11:06:29 am
Karl101, the photodiode must go the other way round in order to work. Think of it like a tiny solar cell, it generates voltage when light hits it. But the cathode becomes the positive source.
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