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16  Using Arduino / General Electronics / Re: criticism over my circuit.. on: April 17, 2014, 12:01:36 pm
SteveSpice still works pretty well. ;')
17  Using Arduino / General Electronics / Re: criticism over my circuit.. on: April 16, 2014, 11:25:22 pm
Don't forget my correction...
18  Using Arduino / Project Guidance / Re: How to increase the dc motor's speed(andFrequency)value more than255(and64KHZ)? on: April 16, 2014, 06:25:31 pm
http://www.ti.com/lit/ds/symlink/l293d.pdf
19  Using Arduino / Project Guidance / Re: How to increase the dc motor's speed(andFrequency)value more than255(and64KHZ)? on: April 16, 2014, 06:25:11 pm
Quote
When I take of this jumper ( at the above screenshot that is on my motor shield ) I can put 1 power supply to power shield and 1 power supply to my arduino at the same time without any problem, right ? thanks.

Yes, that is the jumper I thought you were talking about. Take that off and you can power the motors with their own supply.

The grounds will be connected together through the motor shield, as long as you connect both leads to the Ext_Pwr pins.

As for the current, the two outer ICs are the motor driver chips; read the numbers and Google for the datasheets. I think that might be the same motor shield that I have, it has two L293D chips on it. They are rated at 600mA max, 1.2A peak.

However, without a heatsink, they may get quite hot at 600mA.
20  Using Arduino / Project Guidance / Re: How to increase the dc motor's speed(andFrequency)value more than255(and64KHZ)? on: April 16, 2014, 01:53:18 pm
The motor shield may have a jumper that connects the motor driver chip to the Arduino's 5V.

If you do not remove this jumper and you connect 9 or 12V to the Motor Power Input, you'll be applying this directly to the Arduino's 5V buss and fry it. If you have not removed the jumper and haven't fried your Arduino, it is probably because a small rectangular 9V battery can't supply much power.
21  Using Arduino / General Electronics / Re: criticism over my circuit.. on: April 16, 2014, 01:49:01 pm
Hah! Yeah, I don't think we need to limit "General Electronics" to strictly Arduino related or nothing.

How about this? It relies on only about 15uA pulled from the 5V supply to the base of an NPN, then that draws about 140uA through a resistor from the 14.4V supply. No other power when the 5V supply is present.

When 5V goes dead, the 2nd transistor gets turned on through the 100k resistor. This pulls the base of the 3rd transistor, a PNP, low through a 10k resistor and turns it on. lighting the LED.

The 10k from 14.4V to the PNP base is to make sure it is kept OFF when the 2nd transistor is OFF.

Edit: That first resistor should be 3.3M. Somehow my decimal point got lost... and 1.3uA from the 5V supply. I'd feel more comfortable with a slightly smaller resistor here, like 1M.
22  Using Arduino / Project Guidance / Re: [ Guidance Needed ] How to make my own Arduino. (for USB com) on: April 15, 2014, 03:57:10 pm
Arduino the -best- choice? In what terms?

It should be sufficient. It doesn't take much CPU power to keep up with input from a person.

There are a -lot- of alternatives to ATMega. PIC, Propeller, TI, ST, Freescale, Si Labs, etc. and more etc. It seems like just about every IC manufacturer has their own microcontroller.

For price, TI has an ultralow power 16 bit MCU, the MSP430, some versions way under one US dollar. The Propeller has 8 cores in an 80MHz chip for $8.
23  Using Arduino / General Electronics / Re: criticism over my circuit.. on: April 15, 2014, 12:26:37 pm
How about a CMOS 555 timer? Some aren't meant to run from more than low Vcc, so make sure the one you choose does. Should draw on the order of microamps when the LED is off.

The TS555 is rated to 16V. Just put an appropriate resistor on pin 5 so pins 2 and 6 trigger when the 5V line drops to where you want it to trigger. Built-in hysteresis. It acts as an inverting schmitt trigger.


24  Using Arduino / General Electronics / Re: Running super bright IR LEDs at 38khz off PN2222 on: April 15, 2014, 10:13:05 am
38kHz isn't really fast, though.

I suspect this has more to do with not enough difference between 6V and the total LED drop.

The suspicion that the transistor has C and E reversed is a good one, too. Generally, a BJT will work with them reversed, but at a much lower gain and seriously degraded saturation.
25  Using Arduino / General Electronics / Re: My First Oscillioscope on: April 15, 2014, 10:10:51 am
2M memory vs 40k? Just that alone is worth the extra $100.

As for bandwidth, fungus is right on. Square waves have odd harmonics, the more that get lost, the more it looks like a sine wave. I consider the 9th harmonic the minimum, and the bandwidth is measured where the response is -3dB down, so 10x the square wave frequency is a good rule-of-thumb.
26  Using Arduino / General Electronics / Re: Measure a battery amps on: April 14, 2014, 10:05:59 pm
I think there was a misunderstanding and the OP connected his meter set on Amps directly across the battery.
27  Using Arduino / General Electronics / Re: Running super bright IR LEDs at 38khz off PN2222 on: April 14, 2014, 09:59:48 pm
Measurements....
28  Using Arduino / Project Guidance / Re: [ Guidance Needed ] How to make my own Arduino. (for USB com) on: April 14, 2014, 09:04:01 pm
I think because you edited your first post, it made what followed nonsensical.

The Arduino is open source, so you can look up the schematics here:
http://arduino.cc/en/Main/Products

The other person posted this link to an Arduino on a breadboard, which shows what I was talking before:
http://arduino.cc/en/Main/Standalone

However, that is incomplete. There should be three 0.1uF capacitors added. One each from Pin 7 (Vcc) to ground, Pin 21 (ARef) to ground, and Pin 20 (AVcc) to ground.
29  Using Arduino / General Electronics / Re: Running super bright IR LEDs at 38khz off PN2222 on: April 14, 2014, 08:49:42 pm
TIFF is not a good choice for the web. If you use JPG, we can see your schematic without having to download it.

I'd use a 470 ohm resistor. Right now at best you have about a 40:1 ratio of current. But when you are trying to drive a transistor into saturation, the gain drops drastically. Plus, you want to make sure it is overdriven. I use between 10:1 and 20:1 collector current vs base current. 470 ohms will get you around 8.5mA base drive (voltage out of an Arduino pin drops below 5V when you draw current) for about a 12:1 current ratio.

But then you've eliminated that as the problem with a 220 ohm resistor.

What about your 6V supply? Where is it coming from? What is the actual voltage, both without blinking the IR LEDs and while blinking them?

Do you have an oscilloscope you can monitor this with? What does the waveform on the transistor collector look like?

Your iPhone almost certainly has an IR filter, otherwise plants in sunlight will have their color balance messed up. More likely is that, like every other camera with an IR filter, it just doesn't block out all IR.
30  Using Arduino / General Electronics / Re: can anybody tell me the gain of this transistor for 0.15 amp collector current? on: April 14, 2014, 02:46:40 pm
150mA to the fan. 12V.

The transistor Vbe is about 0.7V. The datasheet rating of 1.3V is a maximum at maximum base current.

To make sure a transistor is saturated, you should put in a base current between 1/20 and 1/10 of the collector current. So about 8 to 15mA. This is because gain of a transistor goes down when in saturation, so the gain at 15mA unsaturated is not an accurate assessment of what it is when saturated. In addition, you want the transistor overdriven so a different batch, temperature, or aging doesn't prevent saturation.


(5V - 0.7V)/10mA = 430 ohms
(5V - 0.7V)/15mA = 287 ohms

The output of an Arduino will not go all the way to 5V when you are drawing current from it, so I'd go with 330 ohms.

Then the Vce saturated should be around 0.1 to 0.2V.

BTW, 15mA is 0.015A. 0.15A is 150mA. The prefix "m" lower case or "milli" means one thousandths.
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