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136  Forum 2005-2010 (read only) / Interfacing / Help pulsing an IR LED with a power MOSFET on: September 25, 2010, 04:54:12 pm


I'm trying to create a circuit that will pulse the TSAL6200 IR LED at 600mA with 600us on/off pulses with the 'on' pulses modulated at 38kHz. I've programmed an 8MHz ATtiny85V to generate the correct PWM waveform, verified to be correct on my scope. I'm powering the whole circuit from 3x1.2v AAA batteries supplying a MIC29152BT adjustable low dropout regulator set to 3V.

According to the datasheet the TSAL6200 will have a forward voltage of about 2.2v at 600mA. Given that the BUZ72L drops about 0.1V the series resistor should be (3-2.2-0.1)/0.6=1.16 ohms. The nearest I have to that is 1.5 ohms which would give 466mA.

The problem I'm having seems to be related to the current drawn by the LED circuit. If I wire up the circuit as in the diagram then the ATtiny85V is not happy at all. As soon as my program initiates PWM on pin 6 then the MCU resets itself. If I substitute the 1.5 ohm resistor with a 10 ohm resistor then the circuit will work (trace below), but the current through the LED is obviously nowhere near the level I'm hoping for.

Any ideas what I'm doing wrong here?

137  Forum 2005-2010 (read only) / Interfacing / Re: X-Band Motion Detector + Arduino on: August 19, 2010, 11:51:58 am
It's designed for a discrete digital read, I connected it to an analog pin because it was more convenient for me. You will simply get triggered = HIGH, not triggered = LOW in realtime as motion occurs within the sensor's field of view.

Basically Parallax have taken the raw radar sensor that you can get on ebay for about $10 and added the amplification and digitization circuitry that make it possible to plug it straight into a microcontroller.
138  Forum 2005-2010 (read only) / Interfacing / Re: X-Band Motion Detector + Arduino on: August 18, 2010, 01:06:40 pm
I have one of these on my breadboard right now. It is trivial to connect to the Arduino. 5V, GND and connect OUT directly to an analog input. I'm using a smoothing function on my readings from the pin whereby I set a minimum trigger threshold, minimum time above the trigger threshold and a maximum time below the threshold to disregard.

It is very sensitive and has a very wide field of view - the datasheet is accurate with its description of the FOV. Any motion in any direction will trigger it. You definitely do not have to be moving towards/away from it.

Because I'm interested only in a narrow field of view I am mounting mine inside a 2" square aluminium pipe - it just fits inside. There is an ebay seller that will include plastic end caps that make for great mounting points.

Glass will present no problem for this sensor - it will go straight through it. In an interior environment it may also go straight through thin walls and detect movement in the next room.

It's a fun sensor, you'll enjoy playing with it.
139  Forum 2005-2010 (read only) / Interfacing / Re: USB data connection question on: August 25, 2010, 03:17:59 pm
Thanks guys. After some thought I've decided to fit a switch that will allow me to choose between external USB power/data and internal power from the battery. I'll lose power to my external components while the switch is in the USB position but I'm not concerned about that because I only need the USB for reflashing the arduino.

PS. it's an Arduino mega1280 clone.
140  Forum 2005-2010 (read only) / Interfacing / USB data connection question on: August 24, 2010, 04:04:46 pm
My device is battery powered. The battery supplies a 5V regulator and the output from that is connected via the black/red wires in a hacked USB cable to the USB port on the Arduino and also to the external components in the device. That works fine.

Now I want to add the facility to communicate with the device from a PC over USB while the device is running on battery. Simple I thought. Just connect D+ and D- on a USB socket to the green/white wires in the aforementioned hacked cable and connect the computer to the socket with a standard USB cable.

Doesn't work, the computer and Arduino behave as if neither exist.

Clearly I have to do something with VBUS and GND on the device's USB socket to get this to work. Anyone know what? I want to keep my device and it's external components running from the battery while talking to the computer if at all possible.
141  Forum 2005-2010 (read only) / Interfacing / Re: Is this a good LCD option from Oscsys? on: August 14, 2010, 03:24:38 am
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The pins are on the bottom of the LCD. All mines have pins on the top. If you just use it to breadboard, fine, if you want to put it on a PCB, make sure that's what you want. I like the ones with pins on the top so I can put the ATMEGA chip and buttons below (not underneath) the LCD. There's still space to lay the wires. Just IMHO.
That's a very good point. When I buy these on ebay I always make sure I get them with pins on top AND bottom for maximum flexibility when it comes to housing them in a box.

(e.g. this one)
142  Forum 2005-2010 (read only) / Interfacing / Re: 2.8" Touchscreen OLED 320x240 C0283QGLH-T 60$ on: August 08, 2010, 01:43:50 am
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right now I think friendlyARM + Micro2440 is the cheapest QVGA color OLED solution
That is the route I'm going down for my project that uses a 320x240 LCD. Develop on the Micro SDK board with all those IO breakout interfaces and when complete deploy the tiny STAMP board with just the parts I need. Running google Android on it provides you with all the graphics libraries you need to create a modern UI. Where did you see the micro for 53 CAD? That's a very good price.

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I am assuming that there are no cheap single chip framebuffers (or is it call a ramdac ?) we can use to generate VGA or NTSC from an arduino right ? (because you can spend a minute drawing a frame if you want if the signal generation is done outside the mcu), is that correct ?
That, in a nutshell, is the problem. The Arduino MCU's are just not designed to be driving devices that need so much data so fast.
143  Forum 2005-2010 (read only) / Interfacing / Re: 2.8" Touchscreen OLED 320x240 C0283QGLH-T 60$ on: August 07, 2010, 03:57:59 pm
Forget about trying to drive a 320x240 colour display from an Arduino (any model). You don't have the RAM to provide the required frame buffer nor do you have the CPU Mhz to do anything other than service the LCD. You need to take a step up to something like one of these
144  Forum 2005-2010 (read only) / Interfacing / Re: Power from external 5V regulated supply? on: July 14, 2010, 01:32:17 pm
Lots of very good information here. Thanks to all for replying.

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You have not revealed WHICH Arduino board you are asking about.
It's a mega clone from ebay: this one. It claims to be the reference design but people claim lots of things on ebay so, based on the cautions given by people here, I'm not going to do it.

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The way I like to supply regulated external +5vdc to a standard Arduino board is to take a spare USB cable, lop off the PC end, locate the positive and minus power wires and wire them to the supply. That way the built in 500ma thermofuse is in play and it no way interferes with the on board auto-voltage components included the +5vdc regulator chip.

I like this idea. Do you tie the data wires to ground or leave them floating?
145  Forum 2005-2010 (read only) / Interfacing / Power from external 5V regulated supply? on: July 13, 2010, 03:29:05 pm
Is it true that you can provide a regulated 5V supply to the Arduino through the 5V pin that you would normally draw power out from? I've seen a few references on the internet that indicate you can do this but nothing from anyone that's actually doing it.

My Mega1280-based project is powered by a 12V battery that goes straight into a TS2940 regulator to provide 5V to the external components. If I can also power the arduino this way then I will because bypassing the onboard regulator will save some power and extend battery life.
146  Forum 2005-2010 (read only) / Interfacing / Re: Analog joystick short circuit question? on: June 10, 2010, 02:14:45 pm
Thanks for the replies guys. I've removed the resistor with no adverse affects and you were right in that I've got the full resolution now.
147  Forum 2005-2010 (read only) / Interfacing / Analog joystick short circuit question? on: June 09, 2010, 03:14:24 pm
Hi all,

I've wired up a PS2 analog thumb joystick as in the tutorial on this website and all is good, I can read and decode the position of the stick from the analog pins.

The question is, in my newbie-paranoia I have wired in a 150R resistor before GND because of my fear of a short-circuit when one of the pots is at zero.

Is my fear unfounded? Can I remove the resistor? Nobody else seems to bother with one. I wired my multimeter in series and it only showed a 1mA current flow through the circuit regardless of the joystick position.

Looking forward to any advice you can give.
148  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: writing to sd-card without any file system(raw) on: January 07, 2011, 07:57:21 am
One approach taken by some devices like the ARM pocket oscilloscopes is to get you to format the card on a PC and create a file of exactly the size you need with a known filename. Then the device interacts with the content of that file as if it were a device in itself ignoring the rest of the filesystem.
149  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: ANSI C IDE for Arduino projects. on: December 30, 2010, 07:58:21 am
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#define __AVR_ATmega328P__
Don't do that. The appropriate macro is set by avr-gcc based on your -mmcu flag. Just make sure you've got -mmcu=atmega328p in CFLAGS. You might also need -DF_CPU=16000000 if you're using any library timing functions. That will solve your issue including <avr/io.h>.
150  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: New Icon? on: September 15, 2010, 03:28:50 pm
As a foil to those clamouring for ARM levels of performance (buy an ARM ffs!), my hope for a new dev board would be something that took in the highly integrated ATtiny range. An Arduino format board with a pluggable ATtiny stamp module in the center would be great. Buy one Arduino dev board and plug in minimal ATtiny modules as required by your project then deploy the stamp module when you're done.

Just my 2d.
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