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46  Using Arduino / Project Guidance / Re: light barrier for airplanes on: August 28, 2014, 08:59:13 am
I'd suggest using an upward-facing USB camera and Roborealm ($50) to identify the passing of the plane. Any other option would require you to attach a beacon (lamp, battery, and circuit) to the plane which would not be acceptable to your plane-flying friends.
47  Using Arduino / Motors, Mechanics, and Power / Re: setup with two stepper motors 28BYJ48 12 V on: August 28, 2014, 08:30:57 am
Those 28BYJ-blah steppers are geared steppers with a ratio near 64:1 (it's actually a non-integer steps per RPM). Because of that you'll only get them moving around 10 RPM. If you're using a belt and pulley (not a leadscrew/threaded rod) system -- like a printer uses -- you might be able to get decent speed. But beware that the cheap steppers you're using aren't incredibly precise and can lose steps.

For best speed with a stepper you want more voltage driving them. The Adafruit motor board, with its L293 chips, is a fairly antiquated architecture and won't give you good performance. You should be looking for ungeared steppers, probably NEMA 17, and a "RAMPS" board with A4988 drivers. These days you can get a full package pretty cheaply.
48  Using Arduino / LEDs and Multiplexing / Re: Led Driver from Adafruit where to buy in Germany? on: August 28, 2014, 08:10:59 am
Also look up tutorials on using the TLC5940. It's only 16 channels (5 RGB leds) but you can get it in a DIP format which is of course easy to work with. You will find lots of sellers of that chip.
49  Using Arduino / Microcontrollers / Re: Standalone Atmega328 locking up on: August 28, 2014, 08:06:39 am
There's a separate cap between AVCC and GND and VCC and GND to help keep the noise from the digital side of the chip and circuit from interfering with the analog readings that are being handled on the analog side of the chip. It's not a necessity but it's important where you require premium accuracy from your analog readings. It's rare to see it but sometimes you'll also see designers building boards where the analog GND and digital GND are kept completely separate and only connect right near the power source.

50  Using Arduino / Project Guidance / Re: Add own atmel controllers on: August 28, 2014, 06:58:25 am

Newark/Farnell have had some really low pricing on the 328's lately.

http://octopart.com/partsearch#!?q=atmega328P
51  Community / Bar Sport / Re: Grrrrr crappy components on: August 26, 2014, 11:33:11 am
So how long did it take you to figure out that the caps were marked incorrectly? That would have been the last thing I would have checked.
52  Using Arduino / General Electronics / Re: 9V Energizer Recharge Battery on: August 23, 2014, 09:14:04 pm
See http://ww2.duracell.com/en-US/Global-Technical-Content-Library/Product-Data-Sheets.jspx for example datasheets. FYI, for the Duracell 9V / NiMH datasheet specifically the X-axis on the second chart ("High rate discharge") is labeled improperly; it should be minutes instead of hours. "1C" means 175ma for your 175mAh battery. "3C" is three times that current (525ma) and the chart shows a ~18 minute lifetime.

If you really need a lot of current you should be looking at lithium polymer batteries; with those you can get cells rated at 20C and much more.
53  Using Arduino / Sensors / Re: Detecting a seed dropping through a plastic tube on: August 23, 2014, 04:53:45 pm
Commercial units use a phototransistor or photodiode and IR LED. Larry's suggestion of using a comparator would be the way to go; then you'd just need to twiddle a potentiometer to get it tuned right. It's well under a dollar in parts.

http://www.buildcircuit.com/experiment-with-lm358/

Really depends on what kind of a planter you have as to what would be the best way to arrange the LED and phototransistor but it appears that commercial units typically have the emitter on the opposite site of the tube facing the receiver. You're going to need to experiment and see what works best.



54  Using Arduino / General Electronics / Re: 9V Energizer Recharge Battery on: August 23, 2014, 04:17:37 pm
9V batteries contain 6, 1.5V cells. I've never seen one that didn't. Your DS2710 is a single-cell charger.

(Remember that a "battery" is composed of "cells")

The best way to charge a battery like this is with a constant current circuit and charging it at a 10 hour rate (175mah / 10h = 17.5ma). Use an analog pin on your Arduino to measure the voltage and cut it off at about 8.4V.
55  Using Arduino / Motors, Mechanics, and Power / Re: Arduino Mega hanging on Solar Power on: August 22, 2014, 05:04:48 pm
Charge controllers usually have separate lugs for the battery connection only for purposes of "low voltage disconnect"; disconnecting the battery from the load to ensure the battery doesn't become excessively discharged. If you think that's a concern then I'd suggest connecting your circuit directly to the battery. You can always use a spare analog port on the Mega to monitor the battery voltage and stop your power-hungry activities when voltage is getting low.
56  Using Arduino / General Electronics / Re: HX711 - Power & Logic lines question on: August 22, 2014, 04:49:49 pm
Your DOUT line from the HX711 to the MCU would assumedly be at 5V levels and more than likely in violation of the limits on whatever MCU you have it connected to.  An AVR is VCC + 0.5V on any IO pin.

I don't see anywhere on the datasheet where resistors are on the data lines (DOUT, PD_SCK).
57  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 21, 2014, 05:52:52 pm
The label states it has "7.5VA" total output. That "VA" refers to volts * amps, so using the 12V output alone it's roughly (7.5VA / 12) .625 amps

Your transistor selection doesn't really depend on the output of the transformer, however, but rather the current consumption of the light or motor that the individual transistor will be switching power to.
58  Using Arduino / Project Guidance / Re: CNC Router equipment on: August 20, 2014, 02:18:27 pm
You use a CAD program (e.g. AutoCAD, FreeCAD) to create a model to cut on your CNC. You then use a CAM program (MeshCAM, PyCAM)  to convert that model into G-code -- a standard language for controlling the movements of a CNC machine. Then you use controller software (Mach3, LinuxCNC, or Arduino-based GRBL) to translate those G-code commands into signals sent to your stepper drivers / spindle control / etc.

When used with CNC the parallel port is just treated like a bunch of I/O pins. Yes, you could wire the step/dir pins on your stepper drivers directly to a parallel port cable if you were willing to accept the risk of accidental voltage spikes or miswiring blowing up your computer, but usually that wiring is done using some sort of parallel port breakout board that includes optical isolation and easy wire connections. There aren't any hard and fast rules that state what pin in the parallel cable controls what function of the CNC machine; this is always set in the controller software. Why the parallel port and not USB? Mostly legacy reasons; nobody has come up with any standards for a USB interface.

When you build your first CNC router I'd suggest starting with a mediocre design. Just use some cheap allthread for your leadscrews and tapped wood/plastic blocks for your leadscrew nuts. Stick with wood for your frame/gantry/etc. What you're going to learn from building this first, cheap machine is going to be extremely valuable when you start planning your second, expensive machine. What you don't want to do is build an expensive machine that doesn't perform well.
59  Using Arduino / General Electronics / Re: Some help with High Powered LEDs on: August 19, 2014, 12:15:11 pm
Your driver can be more than 2V output; it's the current that matters. You do want to use a source voltage and driver that matches the Vf of your LED as closely as possible however.

You need to be careful when selecting a driver that the driver is capable of PWM or "blinking" control. Switchmode LED drivers and most all AC mains-powered drivers will react poorly if you try to toggle power to them using a transistor or such. Make sure the driver you choose has either a PWM input or is otherwise described as dimmable.
60  Topics / Robotics / Re: Multiple Bluetooth/radio receivers on one Arduino? on: August 19, 2014, 11:57:46 am
Whether or not the IR would be filtered would depend on the camera.

Sounds like you should really just cough up the $300 for a Soloshot. I'm guessing that they're using GPS to track the target, and if so, it's not a good solution for indoors.
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