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5746  Using Arduino / Motors, Mechanics, and Power / Re: Limit switch control of stepper motor direction on: February 22, 2013, 07:25:26 pm
You have only one limit switch?  How is that supposed to work?

Also your code is stateless, you need to have the current direction as a variable (which has state).

Currently it will go till it hits the switch and then oscillate as the switch goes on and off in rapid succession.

You need each limit switch to trigger a change in state in the correct direction - not one switch trying to
control both directions.
5747  Using Arduino / Motors, Mechanics, and Power / Re: Rewersing directionof stepper motor with limit switch on: February 22, 2013, 07:18:24 pm
Existing code?
5748  Using Arduino / Motors, Mechanics, and Power / Re: motor draws much current - diabling other components? on: February 22, 2013, 07:17:31 pm
Things are always simpler if you run the motor from a separate supply - then spikes and drop-outs don't bring down
the rest of the system.  Remember a motor can pull its stall current briefly at startup and when reversing direction,
unless your supply can effortlessly handle that current the voltage will drop.
5749  Using Arduino / Motors, Mechanics, and Power / Re: L293D Getting Really Hot, Really Fast on: February 22, 2013, 07:14:05 pm
Well that motor has a design full-load current of 9A (at 24V) and a stall current of 25A (at 16V), so you'll need
a motor controller able to handle those currents (and probably an over-current sensor to detect stalls).  The L293D
can only handle the no-load current really - not very useful.

A motor that size is probably OK to PWM at 4kHz - the L293D won't handle 36kHz efficiently, its has slow darlington
outputs, not MOSFETs.
5750  Using Arduino / General Electronics / Re: how to put components with thick legs onto perfboard on: February 22, 2013, 06:14:59 pm
If its stripboard drill from the copper side to avoid lifting tracks!
5751  Using Arduino / Displays / Re: Sleep and LCD current on: February 22, 2013, 06:10:37 pm
You definitely don't want to power down the display with a HIGH logic input connected - you could
burn out the protection diode (CMOS chips will take all their power from such a pin)   Have you
measured the current consumption with the display on (and backlight off)?

If you power down the display you probably need to re-initialise the driver for it on power-up
anyway, so changing all the pins to INPUT mode and LOW before sleep ought to be reasonable.
5752  Using Arduino / Displays / Re: 1.8 SPI TFT from ebay - problems on: February 22, 2013, 06:05:14 pm
Do you have a link to the actual display?

Perhaps the power supply isn't adequate - measure it with a multimeter whilst driving the display?  How have you
connected it all up?
5753  Using Arduino / General Electronics / Re: first pcb try on: February 22, 2013, 10:48:05 am
I have read this post with great interest. I'm new to the PCB layout and design. For those of you who are drilling your own boards. Where do I find a .08 bit in the USA. What size of bit or bits do I need? Where can I get them? I believe .08 is the correct bit size for most leads.

Thanks



0.08?  Sounds very wrong in mm or in - perhaps you mean 0.8mm?

0.035" or 0.9mm is about right for a range of leads, thin leads and vias can be thinner than this.  eBay has quite a lot
of carbide PCB drills available, but some are ex-industry used drills from the look of things.  For fibre glass carbide bits
are the best.
5754  Using Arduino / Motors, Mechanics, and Power / Re: Problem with Remote control and brushless motors on: February 20, 2013, 07:17:05 pm
Is it possible to log some of the values to the serial monitor as it runs?   Then you can check if pulseIn is returning
what you expect, and whether running the motors is causing interference (a possibility).  Keeping all the servo cables well
away from high-current cabling is important BTW.
5755  Using Arduino / Motors, Mechanics, and Power / Re: Soldering station : Use a TRIAC or MOSFET to drive the heater? on: February 20, 2013, 07:12:01 pm
I think there are also SSR's that handle AC and can do the job.

One argument in favour of the rectification method is that you can then also
run your iron off a 24V battery should you want to.  Don't add smoothing capacitors
otherwise the 24VAC will become 33VDC.  The rectified AC has the same rms
value as the original AC (less a couple of diode drops). 

Alternatively if the secondary output is floating you can use 2 n-channel MOSFETs
source-to-source as an "ac switch" - the two drains are the switch terminals and
you connect the common sources to ground and drive the gates in parallel too.

Should one side of the heating element be connected to the soldering iron casing then
that side will need to be grounded (otherwise the iron tip will be live at 24V) - I don't
believe this ever is the case though.
5756  Using Arduino / Motors, Mechanics, and Power / Re: Opinion on H-Bridge Circuit on: February 20, 2013, 06:56:01 pm
Good point about making sure to test the device at a low current first. I will probably buy 10 and 100Ohm resistors and then test them at a lower amperage to see how much they decrease the PWM.

As for the ceramic decoupling, would putting some capacitors in parallel with the H-Bridge work for this?
I think that's a good start - but watch out for the high ripple currents involved overheating capacitors - low
ESR is important here
Quote

I will definitely make sure to put resistors between the H-Bridge and board, and I will probably also use a relay to prevent shoot through from a programming error
Relays unnecessary - the HIP4081 prevents static shoot-through (it would be a crazy H-bridge controller that allowed it),
but you have to set the dead-time adequately to allow for the time taken by your MOSFETs to switch off.
The datasheet shows the deadtime against resistor value on HDEL and LDEL.  Even shoot-through for 100ns
can blow up MOSFETs if being PWM'd since all the power of the supply is available (augmented by decoupling
caps).
5757  Using Arduino / General Electronics / Re: Specific potentiometer in transmitter on: February 20, 2013, 06:39:42 pm
I know such devices are used in various devices like joysticks and throttle controls, a specialist component supplier like farnell
or digikey would be a place to start as they have the largest component ranges. 
5758  Using Arduino / Programming Questions / Re: How to output a pulse of specific width without using Delay on: February 20, 2013, 06:34:27 pm
Blink without delay relies on millis().  Millis() can't do a 200uS pulse width.

For that kind of precision you need a timer and interrupt.

Or if no other task takes many cycles you could use micros() instead of millis() in a BlinkWithoutDelay pattern.

Some of the timer1 modes might be amenable to do the work - you can setup pins 9 and 10 to switch at
distinct threshold values and you can dynamically change the target count in certain modes cleanly.  Datasheet
for all the grubby details.
5759  Using Arduino / Motors, Mechanics, and Power / Re: Adafruit motor shield - intermittent power to motors on: February 18, 2013, 06:15:49 pm
Perhaps noise from the motor wiring is reseting the Arduino - you have a separate supply from the sound of it,
perhaps the motor wiring runs too close to the Arduino?

You could add a delay of a couple of seconds at the start of setup (), then if it is a reset problem it will pause
much longer before restarting, whereas if its some other issue the behaviour shouldn't change after the first
power-up.   Can you watch the LED on pin13 too?
5760  Using Arduino / Motors, Mechanics, and Power / Re: How do NiCad and NiMh chargers detect -deltaV to stop charging? on: February 18, 2013, 06:04:31 pm
Something that may be of interest (very loosely) is that I was able to revive some Li-on cells that had dropped down to 0.2 volts and wouldn't charge.
http://ajb2k3.wordpress.com/2012/11/18/psp-110-battery-revive/ Not very informative but it did work.

I think Boeing tried that already smiley-wink
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