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1  Using Arduino / Project Guidance / Re: measure rotation of a bike wheel on: January 23, 2014, 06:30:52 am
@ Paul__B - thanks, a really useful answer.   And no I haven't seen any of the videos...  

Whaddaya know, ladyada do a kit smiley



edit: from the ladyada page - "With one spoke, total persistence at 15mph. Two spokes, 10mph. Three spokes, 7mph. (Assuming a mountain bike wheel). Looks cool even if not completely persistant."
2  Using Arduino / Project Guidance / Re: measure rotation of a bike wheel on: January 22, 2014, 07:31:26 am
I'm planning for all the electronics to be mounted in the wheel
3  Using Arduino / Project Guidance / Re: measure rotation of a bike wheel on: January 22, 2014, 07:23:21 am
Hi Dave.  The problem I can see with that is the encode would need to be mounted on the frame of the bike, but I need it to be mounted in the wheel with the rest of the electronics, unless I use wireless communication (which maybe isn't a bad idea)

I terms of resolution I guess maybe 8 steps would be the minimum..
4  Using Arduino / Project Guidance / measure rotation of a bike wheel on: January 22, 2014, 06:40:45 am
Hi.  I'm trying to figure out how to measure the rotation of a bike wheel.  Not just it's speed, but the position it is at at any give moment.

I'd like to mount a bar of leds (and an arduino + sensor + batteries) inside a bike wheel, then track the rotation of the wheel.  I'll use this rotation value to update the leds to create a persistence of vision display.

I know I can use something like a hall sensor to tell every time the wheel finishes 1 rotation, but I'd like more resolution than that, as I image the fluctuations of speed when cycling would make the resulting image jerk around alot.

My best idea so far is to use >1 hall sensor mounted on different spokes of the wheel, with a magnet attached to the forks. I think I'd need quite a few though and it could be cumbersome.    Any better ideas? 
5  Using Arduino / General Electronics / cable connectors on: January 11, 2013, 07:22:43 am
Hi

Can anyone recommend some 4 way connectors that can take 5A and are as small as possible (and available in the uk)

Something like this - http://uk.farnell.com/multicomp/mc000066/plug-3-5mm-r-a-10a-04way/dp/2008039?Ntt=2008039 but with a female part too (neither should be pcb mount, both should be screw terminals or similar)

Thanks guys
6  Using Arduino / General Electronics / Re: Measuring current above 10A on: January 04, 2013, 12:48:17 pm
dc

Can you buy a device similar to a multimeter, with test leads and a digital display?
7  Using Arduino / General Electronics / Measuring current above 10A on: January 04, 2013, 12:41:54 pm
Hi

Both my multimeters will only measure current up to 10A.  What kit would you recommend to measure higher currents, up to about 40A?
8  Using Arduino / LEDs and Multiplexing / Re: make pwm output non linear on: December 12, 2012, 05:15:03 am
I was just thinking about the implications of not having pwm anymore.

Do you know of any drivers or pwm generators that are similar to the ws2801?  Ie can be daisy chained on the spi bus or similar?  I really like how modular and expandable these chips are.
9  Using Arduino / LEDs and Multiplexing / Re: Controlling a stand alone LED remotely on: December 11, 2012, 10:54:37 am
What's the tech in that trick?
10  Using Arduino / LEDs and Multiplexing / Re: make pwm output non linear on: December 11, 2012, 10:48:31 am
Hi dhenry.

Can you point me towards any example circuits that show how to 'utilize a transistor's b-e junction non-linearity' in this way?  Also how do you work out the curve that a particular transistor would give you?

Btw,  I plant use this if possible in two scenarios -

One is pwm source > non linear correction > mosfet (to control 12 led strip)

The other is pwm source > non linear correction > transistor + constant current source (to control a single hight power led)

Do you think your example can integrate with both these systems?


Many thanks
11  Using Arduino / LEDs and Multiplexing / Re: constantcurrentiness on: December 11, 2012, 09:52:12 am
ok, thanks guys
12  Using Arduino / LEDs and Multiplexing / Re: constantcurrentiness on: December 10, 2012, 12:52:00 pm
A lot - something like 9A.

I need 16 outputs, more than the arduino has (pwm).  Maybe a ws2803 (18 channel version of the ws2801) and a n channel mosfet will do the job?


edit - just remembered why I started using the TLC5940 - 12 bit pwm.  Would be really nice to modify the schematic above to use common anode still...
13  Using Arduino / LEDs and Multiplexing / Re: constantcurrentiness on: December 10, 2012, 12:27:19 pm
Thanks Mark, that looks useful for another project.

For this one though, I realised a few posts ago that id don't want constant current as I'm using led strip with integrated resistors!

So I've switched to using a TLC5940 as a pwm source ans a p channel mosfet to amplify the signal.  It works but I've just realised I can't use common anode strip, as described above
14  Using Arduino / LEDs and Multiplexing / Re: constantcurrentiness on: December 10, 2012, 11:50:51 am
Hi Grumpy.

I just built the attached circuit using a p channel mosfet with a TLC5940 to control the 12v led strip.  It works fine with a single channel,  but I just realised that because the strip is common anode, I can't control each rgb channel independently!  How do I change this circuit to allow me to use common anode?

15  Using Arduino / LEDs and Multiplexing / Re: make pwm output non linear on: December 07, 2012, 11:31:01 am
Like I said, if I use a look up table when I only have 8 bits of resolution, the 'jumps' between steps at the bottom of the range are massive, and very noticable
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