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5791  Using Arduino / General Electronics / Re: Difference between 74hc595 and 74hct595 on: February 11, 2013, 02:31:01 pm
You want a high-current 595 replacement like this: https://www.sparkfun.com/products/734

The 74HCT family are like the 74HC but are restricted to 5V supply and have TTL-compatible input
levels (0.8V / 2.4V).
5792  Using Arduino / Motors, Mechanics, and Power / Re: VFD - anyone any experiences or hints? on: February 10, 2013, 04:37:44 pm
Its quite a challenge.  Maybe finding a bargain second-hand VFD would be easier?

Perhaps a forum on electric vehicle drives would be a more fruitful place to ask around - some
people use AC motors for home-brew electric vehicles, 6kW is in that sort of area...

I am guessing a 3-phase PWMable IGBT bridge is the minimal starting point for the
power stage, but you also need some quite sophisticated sensors and control algorithms...
5793  Using Arduino / Motors, Mechanics, and Power / Re: Proximity Sensor and 5 motors on: February 10, 2013, 04:32:00 pm
You need to edit that posting (code is unreadable) and
a) use the # button to get proper code tags to quote the code
b) ensure it isn't getting mangled in the copy/paste operation (preview to make sure)
5794  Using Arduino / General Electronics / Re: LED driver Amperage on: February 10, 2013, 04:27:01 pm
The device by the look of it has 6 identical constant-current switch-mode power supplies.  These are likely to be about 80 to 90%
efficient so you can calculate the power (and thus current) it requires from the nature of the loads (LEDs) you connect it to.

So if you connected one of them to a string of 4 white LEDs at a setting of 700mA, and assuming each LED has about 3.5V
forward voltage, then it will output 14V at 0.7A, which is 9.8W.  You can assume then that about 11 to 12W is needed at the
input to support that, and at 24V than means about 500mA from the supply for just that channel - sum for each channel.

(I haven't checked the ratings for the device, I don't know what output voltage range it can handle, nor the max power
per channel, nor the actual efficiency, but that's the sort of calculation you use with switch-mode supplies:
  power in = power out / efficiency)
5795  Using Arduino / General Electronics / Re: unknown parts on: February 10, 2013, 04:19:25 pm
#1 not sure - need a better photo.
#2 LM35 temperature sensor (can just resolve the lettering)
#4 Almost certainly electrolytic capacitors, but we can't see the relevant info on can - just the manufacturer's logo
#5 Probably IR LED (possibly a photo-diode or photo-transistor)
5796  Using Arduino / Programming Questions / Re: pin-11 dysfunction on: February 10, 2013, 04:13:02 pm
Without more information (the complete sketch) its impossible to guess.
5797  Using Arduino / Programming Questions / Re: Problem with analogRead() on: February 10, 2013, 04:10:54 pm
Add a resistor (about 10K) from pin 7 to Arduino +5 volts.

edit: as AWOL said

Since the button is connected to +3.5V that won't work - use a pull-down to ground.  3.5V will consistently
read as HIGH when the button is pressed.   You need the resistor to pull the pin back down to 0V when the
button is released.

Unconnected inputs on CMOS chips are like radio antennas, they pick up any nearby signal very easily
since they are almost perfect voltage sensors with infinite resistance (well thousands of megohms or more).

Why 3.5V?  Perhaps you mean 3.3?
5798  Using Arduino / General Electronics / Re: Detecting when a LiPo battery connected trough a step-up board has low power. on: February 10, 2013, 04:06:52 pm
I'd include the resistor, something like 1k to 10k is fine, just to prevent the risk of accidental short(*) on the traces of the Arduino
grounding the LiPo - massive currents would then flow, vaporising pcb traces.  LiPo's can put out 50 to 100A or more if abused...

(*) Accidentally put the board down on top of something metal for instance.
5799  Using Arduino / General Electronics / Re: what the flux? on: February 10, 2013, 08:31:02 am
Any chlorinated solvent should be used with plenty of ventilation...  Or avoided(!)
5800  Using Arduino / General Electronics / Re: Piezo Sensors + LED Strip = Weird readings on: February 10, 2013, 08:28:46 am
There may also be electromagnetic induction causing interference from the LED circuit to the piezo.  PWMing a lot of LEDs
means a lot of EMI unless the circuit is shielded - each time the LEDs are switched on and off the rate-of-change of current
can be 10^8 amps/second or so - this will induce voltages in nearby circuits (as Faraday discovered).

Move the LEDs away from the piezo element.

Don't have open loops - these are bad news as the strength of interference is directly proportional to loop area -
always run your wires in a tight bundle, preferably twisted together (but separate bundles for LEDs and piezo,
of course!).

For instance the two wires from the MOSFET to the LEDs should be a twisted pair.  The wires from MOSFET to the 12V supply
should be a twisted pair.  There should be decoupling capacitors on the 12V rail right next to the MOSFET (at least 10uF,
100 would be better), to reduce the radiation back up the 12V supply wires.  Even though the MOSFET isn't directly
connected to the +12V rail you should run the 12V wire up to it, then away again to the LEDs.
5801  Using Arduino / General Electronics / Re: Too many shift registers? on: February 10, 2013, 08:20:39 am
For LEDs which are relatively high current loads switched at logic speeds (5ns perhaps) I'd use 0.1uF + 10uF per chip,
and 100uF+ for the whole board.

Switching many LEDs simultaneously could be causing a rate-of-change of supply current of the order of 10^8 amps/second,
way beyond what a voltage regulator on a remote board can handle, so in a microsecond or so those 0.1uF capacitors are
drained and the circuit malfunctions - before the voltage regulator has time to adjust to the new load (which might take many
us).

The extra decoupling should hold the supply voltage up for long enough.
5802  Using Arduino / General Electronics / Re: Reflow oven (aka Toaster oven) modification on: February 10, 2013, 08:04:47 am
I use a bright torch to watch through the window - its a 12W LED in fact!  Intense point source lighting helps bring out
the shiny beads of solder as they melt.  Of course an LED isn't compatible with high temperature, but a small 12V halogen bulb
would be, there are holders for them with glass-fibre insulated wires too.

Some pictures of the conversion to top-side elements are in posting #44 here: http://forums.parallax.com/showthread.php/130196-How-I-do-SMT-soldering-in-toaster-oven/page3?highlight=toaster%20oven
5803  Using Arduino / General Electronics / Re: Struggling to understand the basics of a 7 segment display common anode on: February 10, 2013, 07:58:51 am
Incidentally the 3V3 rail isn't a good choice for LEDs since

a) Low current only, might not be able to drive many segments at once
b) A bit too low a voltage for blue and white LEDs - may only be able
   to light up dimly...
5804  Using Arduino / Programming Questions / Re: Port Manipulation problem on: February 10, 2013, 07:53:52 am
Humans find binary constants hard to read, hexadecimal notation is easier once you are used to it IMO,
since it groups in sets of 4 bits its harder to slip up by one bit (you can slip up by 4 bits though, but only
with long values in practice).  Its also far far easier to memorize a hex number, even temporarily.
5805  Using Arduino / Programming Questions / Re: Delay question on: February 10, 2013, 07:38:57 am
Which Arduino board?  There is no way to shutdown the USB chip on boards such as Uno and Mega AFAIK,
so putting the microcontroller into a sleep mode won't drastically reduce current consumption.  Usually you'd
need an real-time-clock chip if going that route as running the microcontroller's 16MHz clock is a large part
of the current consumption.

Its worth searching these forums carefully there have been several lengthy threads on this sort of thing.

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