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16  Using Arduino / Motors, Mechanics, and Power / Re: How to have external power to a relay module? on: July 15, 2014, 12:05:30 pm

Your relay board features optical isolation so that section would be pertinent to your requirements.
17  Using Arduino / Motors, Mechanics, and Power / Re: higher frequency of PWM/PPM for ESC on: July 15, 2014, 12:03:43 pm
There's gotta be some confusion here as to the definition of "Refresh rate". The signal you're showing in your pictures certainly isn't 50Hz, or if you're attempting to make those pulses eight times more frequent they're just not going to fit.
18  Using Arduino / Sensors / Re: Tips for measuring speed of ball on: July 15, 2014, 02:48:28 am
You can use two laser pointers and two ldr resistors.

Don't use LDRs (light dependent resistors) for this; they don't react quickly enough for something fast and small like a ball. A phototransistor/photodiode of some type is definitely preferred.
19  Using Arduino / Sensors / Re: IR break beam sensor on: July 15, 2014, 02:44:22 am
You want the part TSSP58038 or TSSP4038. The TSSP58328 is OK, but you have to send it specially patterned codes rather than the plain, boring, 38KHz signal that the 58038 or 4038 allow.

Then read:

You can create a 38KHz beam with a 555 timer or an ATTiny or such. Just depends how cheaply you need to make your transmitter where size or price is an issue.

You can reliably expect ~3' distance with a 20ma red LED as the emitter, 6' with a 20ma white LED, 10' with a 20ma IR LED, and "lots" of distance using a cheap, red laser pointer.
20  Using Arduino / Project Guidance / Re: LED Lightsaber Build Power/Driver Question on: July 14, 2014, 05:32:52 pm
Honest question: why does this circuit work? You have four strings of 16 LEDs in parallel, being fed by a constant current driver, but no single LED goes into a runaway that takes down the string?
i don't understand much your question can  you explain more?
If you set 16 LEDs in parallel you're making an incorrect assumption that they'll share the current equally. Inevitably one of them will consume more than its share of current and it will burn out. Then when any single one burns out you still have the same total current (320ma) but that's now being shared by only 15 LEDs -- the LEDs will start experiencing a cascading failure. 
21  Using Arduino / Networking, Protocols, and Devices / Re: Unique sequential ID on a network on: July 14, 2014, 12:03:49 pm
Typically the router will not reassign the address for a period of days waiting for the machine that used it previously to come back. If you had a router running OpenWRT or such you'd have the configurability to knock that down to much shorter times -- down to just a few seconds if it was required.

But you highlight an important point; if boxes 1 to 4 go down, what period of time do you want to wait before boxes 5 to 8 reassign themselves as boxes 1 to 3? Figuring out the algorithm for all that stuff to work is not at all a trivial problem; the best solution is to avoid the requirement that the live boxes are always numbered starting at 1.
22  Using Arduino / Networking, Protocols, and Devices / Re: Unique sequential ID on a network on: July 14, 2014, 11:24:08 am
This sounds like DHCP. An Arduino comes on line with ethernet and is automatically assigned an IP address by the router. The range of addresses would be configured in the router.

If you don't use DHCP you need to be careful with race conditions. If one or more devices comes online at the same time (e.g. after power outage) they could all check to see if "ID 1" is in use and finding that it's not they would all start using "ID 1" at the same time. DHCP was designed by smart people and already has that type of problem covered.
23  Using Arduino / General Electronics / Re: digital pots ? on: July 14, 2014, 11:13:14 am
Digital potentiometers are only designed for a very small amount of current.

Typical approach for controlling one or more LEDs in series:
24  Using Arduino / Project Guidance / Re: proportional hydraulic valves control with arduino on: July 14, 2014, 01:21:00 am
Unless you're using a valve that has a fancy PWM signal input and requires a specific frequency you're probably on the wrong path. PWM is a duty cycle; the ratio of time that the signal is high vs. low. The granularity of the switching on/off (the PWM frequency) is not likely to be an important factor and the Arduino's default ~500Hz should be fine.
25  Using Arduino / Motors, Mechanics, and Power / Re: Building an H-bridge for very high current Stepper Motors. on: July 13, 2014, 02:40:34 am
Your mosfets are designed for ~10V at the gate before they will fully switch "on"; if you look at your datasheet you'll see the specs typically quoted a 10VGS. This is why you saw such a dramatic increase in current when you moved from 6V to 12V. A logic level mosfet (e.g. IRL540) is what you want when controlling the gate with an Arduino.

If you're really looking to build a high performance H bridge the you'll want to study up on "mosfet drivers". These are designed to drive mosfet gates from logic level signals and then do so with high voltage and current for fast switching times. An IR2181 (you'd need two for a full bridge) would be an example of what you're looking for.
26  Using Arduino / Project Guidance / Re: Visually recognize a number - dumb energy meters on: July 12, 2014, 09:52:15 pm
An optical mouse sensor reads 16x16 pixels (typical). But again it's a problem of getting the right focus on the dial. And finding a compatible mouse sensor :/
27  Using Arduino / Project Guidance / Re: Solar Charging Circuit for Onboard NiMH Charging on: July 12, 2014, 09:44:32 pm
With the panels in parallel with the battery the voltages will always appear to be the same as the battery voltage.  You should think of the panels as outputting a wattage rather than a voltage; for a fixed amount of sunlight the voltage will appear high when little current is being drawn or low when a lot of current is being drawn. Your panels might have an "open circuit" specification which refers to the maximum voltage they will output when no current is being drawn.

For a single NiMH cell, 1.3V is the 90% charged voltage, so you'd configure the TL431 to conduct right around (4 * 1.3V =) 5.2V.  If the batteries are not fully charged then they should absorb all of the current from the solar panels (minus whatever your Arduino is using). If your batteries are fully charged and you're in full sunlight then the TL431 is going to be conducting the full rated current of the panels.

Batteries can typically fully absorb a current equal to 1/10th their capacity without any problem. Your cells are 350mah and your panels are 35ma so it's a perfect combination.
28  Using Arduino / Project Guidance / Re: Solar Charging Circuit for Onboard NiMH Charging on: July 12, 2014, 01:09:53 am
Basically I'm saying you want to eliminate everything between your solar cell and your battery to keep your charge efficiency up. You could get rid of R1 and the transistor, simply leaving the zener between Vin and GND. When the solar panel charges the battery over it's upper voltage limit the zener will start conducting current to GND and keep the battery voltage within limits. A 1/2W zener should handle the current fine. And again you wouldn't need R2 because in a full sun situation the zener should be preventing excess current from reaching your battery. Just don't use too many solar cells to keep things within limits.

A TL431 (very common part) will give you more precise and adjustable regulation than a zener. It is spec'd for 100ma (150ma max) and again would be plenty for multiple panels. Plus, for future needs, if you have TL431s on hand you'll never have to worry about having the right voltage zener around.

Regarding the "LM314", assuming you meant an LM317, you'd want to avoid that part to keep your efficiency up. The LM317 has a dropout voltage around 1.5V, meaning that 1.5V times your current is lost to heat, or your battery always has to be 1.5V higher than your output voltage. An LM1117 has a lower dropout voltage (around 1V), or you can always find more modern parts like a LM2931 with just .16V dropout.
29  Using Arduino / Project Guidance / Re: Solar Charging Circuit for Onboard NiMH Charging on: July 11, 2014, 04:19:04 pm
Regarding your original circuit, you have a strategy that allows current through to the battery when the battery voltage is lower than your zener setpoint. I'd suggest rearranging it so that you shunt current to ground when the voltage is higher than the setpoint. The advantage to that is you keep the transistor, etc. out of the current path and improve your efficiency when charging.

If you have an available analog and digital pin on the ATTiny you could also program the ATTiny to dump current when voltage gets too high. I.e. read the battery voltage and if over the programmed limit activate the transistor to dump current through a resistor, etc. That would offer a bit more control than relying on zener diodes and their imperfect nature.

30  Using Arduino / Project Guidance / Re: Robot Submarine Project on: July 09, 2014, 11:40:41 am
Motor boards with L29x chips are really old tech. An RC ESC is a much better and more efficient choice; you can find them for either brushed or brushless motors (but the OpenROV site probably already explained the advantage of brushless motors).

The Servo library is used with RC ESCs.
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