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1  Using Arduino / General Electronics / Re: Pull-up interference from DCC system? on: August 19, 2014, 08:04:40 pm
Or you can run the drill backwards a little bit to lose the torsion.  With short lengths
a hand-drill gives much more tactile feedback.

I hope you didn't have to strip and solder them too!  (Or make litz wire!)
2  Products / Arduino Due / Re: Tone output on Arduino Due on: August 19, 2014, 08:00:49 pm
I'm sure this can be done, I fear it will take some in-depth reading of the datasheet
about how to configure the timers so that the period can be safely updated on the
fly.  The way this would normally be achieved is a mode that only makes the register
update live as the counter resets to 0, which stops the counter escaping from current
range of counting since 0 is always valid no matter how short a period.

It may be that this works or almost works already, I've only glanced at the timers
(the PWM unit I know better - it might be work a look).

Another way to solve the problem is configure one timer to interrupt at a high rate
(perhaps 100kHz or something like that) and drive a DDS loop.  However that
forces your output transitions to always be on an interrupt tick, which might
not be good enough.
3  Products / Arduino Due / Re: Conversion for the DUE on: August 19, 2014, 07:53:23 pm
Perhaps it would help to say what the problems are specifically?
4  Products / Arduino Due / Re: Due Audio Line Level Interface Circuit on: August 19, 2014, 07:52:07 pm
The caps need to be 1uF (plastic film or electrolytic).

0.1uF will attenuate the bottom 3 octaves.

Ceramic is a bad idea for audio (microphonic, non-linear), 0.1uF invites use
of a random decoupling cap that's lying about!
5  Using Arduino / Motors, Mechanics, and Power / Re: H-bridge on: August 19, 2014, 07:45:36 pm
If I was designing an H-bridge of this sort of size I'd just reach for the trusty
FAN7388 to do all the MOSFET driving (its 3 high-low drivers in one package),
so the component count would be:

4 n-MOSFETs
1 driver chip
2 bootstrap caps
1 decoupling cap for driver
2 bootstrap schottky diodes
[ and some motor supply decoupling too, probably ]

However the FAN7388 is SMT only, so you'd need to be able to handle that.
Current sensing is also a very good thing to have if running from big
batteries.
6  Using Arduino / Motors, Mechanics, and Power / Re: DC PID motor controller on: August 19, 2014, 07:38:08 pm
At 3000 rpm the speed will be constant enough to work as I describe - each rotation
you measure the speed and adjust your pixel clock to match (assuming you can control
that).  The speed isn't going to fluctuate much from cycle to cycle due to inertia, but
will vary on longer timescales.

If you do a PID loop you need a low-noise source of information about speed, since
a PID loop amplifies sensor noise quite markedly - however at that speed a single
cycle is only 20ms which isn't a crazily low rate to run a control loop.

Perhaps use the error in rotation period as the input to the PID loop (simpler
than estimating speed).  The inertia of the system will work to your advantage.
7  Using Arduino / Motors, Mechanics, and Power / Re: Nema 23 driver for 400 RPM on: August 19, 2014, 07:29:54 pm
Mis-stepping is usually caused by resonance, an unloaded motor will behave differently
to one under load (so firstly test the motor under its actual mechanical load).

x8 or x16 microstepping is going to reduce resonance I suspect, so try those settings.

Try a 40V supply - the supply voltage has to be enough to overcome the back-EMF of the
motor spinning at your desired speed - alas stepper motor manufacturers are very
coy about advertising their back-EMF/rpm ratings so this usually has to be measured.
(Note the driver you has an abs. max. supply of 45V so even 40V is at the limit)

Your motor is unfortunately not a very high performance one, as its 9 ohm.  A good
NEMA23 motor would be 0.5 ohm or so and need 3 or 4A of drive.  Such a motor would
probably perform fine for your purposes at 24V (but need a beefier chopper-driver).

In theory a 9 ohm motor is as good as a 0.5 ohm motor if driven from about 4
times the voltage...
8  Using Arduino / General Electronics / Re: Pull-up interference from DCC system? on: August 19, 2014, 07:19:39 pm
Ok thanks for that. Looking on the net, it seems cat5 cables are a lot easier to get hold of than simple twisted pair wires so I might try them.

Although I suppose if I twisted the two single cables I've already got it would do the same job...? If they're long enough.
You can easily make twisted pair using a hand-drill and a bench-vice.
Quote
EDIT:

When you say I've created a magnetic loop, do you mean in the DCC bus cables around the layout, or in the extended wires to the pull-up pin?
All loops are magnetic antennas by virtue of being a loop.  The larger the area the
worse the interference (the better the antenna).  Twisted pair keeps the area very small
and the alternating bits of loop sign-cancel so the level of interference is very low.

The train track is itself a very strong emitter of interference and you should keep your as much of your sensor wiring as far away from it as you can - run the wires away from the
track, before turning parallel to it.  Parallel is the worst configuration for cross-talk.

9  Using Arduino / General Electronics / Re: Ground Loops Galore (SPI Application) on: August 19, 2014, 07:10:13 pm
Trying to run the SPI lines with no ground is the fault.

You must accompany every logic signal wire with its ground, preferably as a
twisted pair if going any distance (20cm or more).   At a pinch you can get away
with one ground wire shared between SCK/MISO/MOSI, but it must be bundled
with those wires in close proximity.  This is signal ground and at logic
speeds its absolutely vital.  The original diagram shows a complete lack of signal
ground on the SPI bus.

With a long SPI run you are going to have to consider signal termination too.
If you don't know what termination is stick to short SPI runs (50cm max?).

What total current is your supply wiring taking?  How long are the cable runs?
Are they twisted pair?
Have you measured the voltage at each board/module?  Do you have a large
decoupling capacitor per board (47uF perhaps)?
10  Using Arduino / General Electronics / Re: LED behavior changes when moving hand near or touching on: August 19, 2014, 06:59:37 pm
LEDs especially need good decoupling since they carry much larger currents than
most logic level signals but switch just as fast - suggest 0.1uF for every chip, 10uF
for each board, minimum.
11  Using Arduino / General Electronics / Re: 12v clipping to a 5v (pulled high) input on: August 19, 2014, 06:56:36 pm
I need to work it out for myself whats going on.

I think in that diagram if you use 5v rated diodes, the bottom one will pull anything over +5v positive to ground, and the top diode will pull anything over -5 negative to the positive rail..therefore the 22r works.

Going to experiment with a 5v rated diode to try to reduce the negative voltage because it basically stops all the positive, which is what i want. Thanks all.
20V, 40V, 100V, makes no difference so long as it only lets current flow one way.

These are _not_ zener diodes, they are schottky diodes.
12  Using Arduino / General Electronics / Re: Some help with High Powered LEDs on: August 19, 2014, 06:47:35 pm
You don't understand what "fast" means to electronics.  Think 50MHz and up!

OK, that's debatable, but using an adjective instead of a number is likely to lead
to confusion in an area of technology where values vary of many many orders of
magnitude.  A fast relay might be 2ms, a fast logic gate might be 0.8ns...
13  Using Arduino / General Electronics / Re: GPS: can you lock on to same Satellite? on: August 19, 2014, 06:40:53 pm
GPS receivers determine which satellites are in view from the
almanac data and try to tune to all those that are, locking on
to any with a strong enough signal I believe.

Since individual satellites can drop out receivers try to get more than
enough in lock, the max number of channels depending on the
chipset.

You need 4 satellite signals to get a full fix, more also reduces the
error circle as well as increasing robustness to drop-out.
14  Products / Arduino Due / Re: util/delay.h library reference is not working with DUE on: August 18, 2014, 04:24:33 pm
The error is correct. util/delay.h is part of the AVR library and the Due is not based on AVR but rather ARM. If the TCS34725 library depends on that AVR header then you will probably have to modify it. There are plenty of delay functions built-in for the Due so you can probably find a way to modify the library to not need any additional headers for delaying.
where can i find these in built functions for the due?? i would like to modify a certain library..(adafruit fingerprint) for the due.. any help would be appreciated..
In the sources?  Its open source, you have the sources, have a look/grep through them.
15  Products / Arduino Due / Re: millis() not working on DUE on: August 18, 2014, 04:22:13 pm
I just grepped the sources - there's a " time_t time ; " declared somewhere
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