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16  Using Arduino / General Electronics / Types of Opto-isolators on: January 27, 2013, 03:15:52 am
I'm currently looking to buy some opto-isolators, however, I see a lot of different types and I'm not sure what the best choice is. The types I've seen are Regular (no details), Darlington pair, TRIAC, and Zero Cross TRIAC.

The first two I think I understand

Regular Opto-isolator= LED inside turns isolated photo transistor on
Darlington Pair Opto-isolator= Same as regular but with higher gain (therefore higher current transfer ratio)

It's the second two which I'm not so sure about
TRIAC opto-isolator= Same as regular but is bidirectional for AC circuits
Zero Cross TRIAC optoisolator= Zero Cross detection? good for AC dimmers.

I don't understand how the ZCD TRIAC optoisolator works. Is a TRIAC opto-isolator always more advantageous than a regular optoisolator. For example can a MOC3062 (pictured)

 be used as a regular DC optoisolator to turn an isolated LED on off with a PWM signal, or would it not work at all since there is no actual zero crossing?
17  Using Arduino / General Electronics / Re: Questions regarding Voltage regulators on: January 22, 2013, 06:22:00 am
Thanks CrossRoads for the insightful read about V.reg damage. Thanks everyone for the advice regarding the battery and daisy chaining regulators too. It is a standalone Atmega328p project as some of you may have guessed. I currently use a power jack but the the thought of using a 9V battery crossed my mind since I have some spare rechargable 9Vs but I will look into the better suited alternative batteries.
18  Using Arduino / General Electronics / Questions regarding Voltage regulators on: January 19, 2013, 10:14:06 pm
If a positive voltage is applied to the output pin of a LM7805 voltage regulator while the input pin is left floating (with 10uF capacitor to ground) will this damage the regulator?

If I want a 3.3V supply from say a 9V battery is there any disadvantage in using the output of a 5V regulator as the input of a 3.3V regulator rather than wiring the battery straight to the 3.3V ?
19  Using Arduino / General Electronics / Re: Multiple pushbuttons and pulldown resistor on: January 19, 2013, 08:50:31 am
If you are worried about power consumption it is a very good practice to enable the Pull-Up resistors on ALL unused I/O pins.  Otherwise, floating pins can draw over 1mA of current.  Which, on a device that only consumes 20mA is pretty significant.

I know this is an old thread but can somebody please elaborate on this. Does this mean all unused pins should be grounded to lower power consumption? If so, would this also mean one has to be extremely careful not to set a pin as output inadvertently, otherwise you run the risk of an overcurrent on that pin?
20  Using Arduino / Interfacing w/ Software on the Computer / Re: bluetooth on: January 14, 2013, 03:20:28 pm
can you elaborate on how you have set up your linux machine and how you listen for incoming data on rfcomm0?

Does it make a difference if you use Serial.print("Hello") instead?
21  Using Arduino / Interfacing w/ Software on the Computer / Serial Monitor works with FTDI but crashes with bluetooth Module on: January 12, 2013, 12:25:30 am
Using a HC-05 bluetooth module I cannot enter commands with Serial Monitor (serial monitor hangs) but Tera Term seems to work with this script

char INBYTE;
int  LED = 13; // LED on pin 13

void setup() {
  pinMode(LED, OUTPUT);

void loop() {
  Serial.println("Press 1 to turn Arduino pin 13 LED ON or 0 to turn it OFF:");
  while (!Serial.available());   // stay here so long as COM port is empty   
  INBYTE =;        // read next available byte
  if( INBYTE == '0' ) digitalWrite(LED, LOW);  // if it's a 0 (zero) tun LED off
  if( INBYTE == '1' ) digitalWrite(LED, HIGH); // if it's a 1 (one) turn LED on

I've set the baud rate appropriately, I think I must have because tera term seems to work at that baud.
Any ideas? Alternatively is there a way of making tera term behave more like serial monitor? i.e inputting a string of commands which are sent when you press the return key.
22  Using Arduino / Project Guidance / Re: Adding a push button to a dual motor control sketch on: January 11, 2013, 05:35:07 pm
when you say "not start from a different part" do you mean releasing the button simply pauses the sketch where it is and then continues from where it left off when you let go?
23  Using Arduino / Motors, Mechanics, and Power / Re: Bipolar Stepper Motor, Does polarity matter? on: January 01, 2013, 07:44:49 am
Thanks for the explanation everyone. That makes sense since the phase shift would be equal but opposite when the wires are switched.

Could I also ask, would this be true for any 2 phase motor, even 2-2 phase unipolar motors in bipolar mode?
24  Using Arduino / Motors, Mechanics, and Power / Bipolar Stepper Motor, Does polarity matter? on: December 31, 2012, 09:21:55 am
I have an Easy Driver and a 4 wire bipolar stepper. I was wondering if the polarity of the AA, BB connections matter.
What I mean by that, say I had four wires A1 A2 B1 B2

would switching A1 and A2 have any effect?
25  Topics / Robotics / Re: Robot arm, need help on: December 30, 2012, 09:21:34 pm
Having 5 arduinos connected to the RPi is no problem though as Drew already said you need to ask yourself why you need it.

You can also use a bluetooth dongle on the Pi and communicate with a bluetooth module on your arduino so that too is possible but I think the biggest obstacle would be the actual communication protocol between your RPi and arduinos. For example how you will send commands like "finger 5 open half way". To be honest I don't know what the best way of doing this is myself. Especially if you plan to have several remote arduinos it might mean you need to pair with all of them and have several bluetooth virtual COM ports maybe? How would commands be sent? through firmata? I think it's best if you explain your main goal to determine if the approach can be simpler.
26  Using Arduino / Project Guidance / Re: multiple motors solenoids _ 1 arduino _ accelstepper on: December 26, 2012, 08:16:08 pm
False. If i am running 3 motors simultaneously using 3 separate H-bridges. I will definitely decrease the top speed that any motor can reach.

You seem quite sure about that, which is surprising given that just yesterday you were asking whether it would make any difference. What effect is it that you think will definitely decrease the top speed?

The speed at which the atmega itself executes instructions will limit speed for a given mode.

For example this is a quote from Brian Schmalz (creator of the EasyDriver) with an accelstepper example:

If you run this code, you may find that the acceleration and deceleration are not quite as smooth as with a single motor (on an Arduino - again, this problem doesn't occur on chipKIT) - that is because our two maximum speeds (3000 and 1000) are pretty high for the ability of the processor to handle them. One solution is to make your max speeds lower, then switch from 1/8th microstepping to 1/4, half, or full step mode. If done right, you'll see the same shaft rotation speeds, but with less CPU load (because you aren't generating as many steps per second.)

As for the initial question of avoiding delays or while loops; as far as I know and I could be wrong accelstepper does one (micro)step for every so you can't avoid long while loops. I think there is no reason why you can't use Attachinterrupt() or an ISR function though. If there is a better way with the accelstepper library then I too would like some info on it as I'm currently doing a similar thing.
27  Using Arduino / Microcontrollers / Re: bootloader on atmega328p-pu, USB FTDI Bitbang on: December 11, 2012, 12:56:49 pm
Well something might get destroyed, but most likely the FTDI basic module. The Spark fun schematic for the FTDI basic says it's default wiring option is set for 3.3vdc and wiring that to your +5vdc power bus on your breadboard is sure to be dramatic for the FTDI module! Simply don't use a jumper wire connecting the FTDI's power pin to your breadboard, just leave it unconnected. Also you should modify the FTDI basic to utilize +5vdc signals rather then it's default 3.3v signal levels, the FTDI basic schematic shows where you can cut  a trace and solder a different trace option to force the FTDI to use +5vdc signal levels.

Sorry about that, I should have made it clear that the power adaptor will not be plugged in when the FTDI basic is connected to a USB port. I also have an FTDI Basic variant with a jumper pin (no soldering, the type you find on motherboards) and have set it to 5V. However I still think that the regulator will be killed but I'm not sure. I guess one way of finding out is to just try it but what would the symptoms of a voltage regulator killed by reverse bias be? would it not pass any voltage at all anymore or would it pass an unregulated voltage?

I was thinking of replacing one wire like this so that Vcc is on the other side of the regulator.

However, I've read that a voltage regulator must be fed with a voltage slightly higher than your target (5V) so if the USB Vcc is 5V (already regulated?) then this is not wise, correct? I guess another option is a diode but I don't have any so I'm looking for an alternative.

I've read you can use the FT232RL on the FTDI basic in bitbang mode to burn a bootloader. Unfortunately all the tutorials seem dated and I can't get them to work:

The Android-IDE keeps throwing errors at me so I was wondering if anybody has had any success or if it's still possible.
28  Using Arduino / Microcontrollers / bootloader on atmega328p-pu, USB FTDI Bitbang on: December 11, 2012, 10:14:20 am
Hi everyone, I'm new here

I also have little experience with electronics so I thought I'd start out by building a breaduino. I've scoured the internet trying to learn and while putting it together I encountered several problems which I cannot find answers to.

My breadboard looks like this

So I have two questions

1) Am I right in thinking that if I connect the FTDI basic to the black header directly below it on the breadboard a reverse-bias will destroy my 5V regulator?

2) More importantly, is it possible to burn the bootloader on to the blank atmega382p with the FTDI basic alone?
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