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

dc

Can you buy a device similar to a multimeter, with test leads and a digital display?

Hi

Both my multimeters will only measure current up to 10A.  What kit would you recommend to measure higher currents, up to about 40A?

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.

What's the tech in that trick?

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

ok, thanks guys

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...

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

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?

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

Non sure if I'm phrasing this well, but is there a way to take a pwm signal to drive an led, and using external components, introduce a non linear curve into the effective current that flows through an led?

The desire is to apply gamma correction to a dimmable led setup, but I dont' want to do it in software, as there is not enough resolution in 8bits to have a smooth 'bottom end' when using this (ie lookup table on arduino) method.

So basically, is there a hardware way to allow me to make more use of those precious 8 bits?

Thanks Grumpy.  All made sense and I got it working.

A thought though -  When using led strip like https://www.sparkfun.com/products/10259  Is a constant current driver not the best solution? I've configured a driver circuit to work with a particular length of strip, but now if I want to use a different length, requiring a different current, I'd need to change the value of the current setting resistor.  Is this correct?

If so, is this a situation when a constant voltage circuit is more suitable?

I'm trying to understand the circuit in figure 12, on page 6 of this data sheet - http://www.onsemi.com/pub_link/Collateral/NSI45090JD-D.PDF

'Dimming using PWM'

I want to use this constant current led driver with a ws2801 pwm driver (also cc) to allow me to control higher power leds with the ws2801, while retaining constant current functionality. I'm loaded with questions -

- What are the two resistors doing in this circuit, and how do I calculate their value?

- Am I right in thinking that while I can have an arbitrarily long chain of leds by supplying sufficient voltage, the maximum current through those leds (and therefore the ccr driver) can be 160mA?

- If need more current capacity than this, I see I can use 2 ccrs in parallel, which presumably will double this to 320mA.  What is figure 11 illustrating then with the use of a resistor on one ccr?  Is it used to set the max current to some value betwwen 160 and 320mA?

- If I need still more current than this, is there a better product or technique I could use? (bearing in mind the source is a pwm signal)

Thanks!

The RS485 chips are easy to use. No microcontroller communication required.

I've used these recently - http://uk.rs-online.com/web/p/line-transceivers/7327958/

They just need 5v, gnd, and the data signal input.  This outputs a balanced signal pair which goes down a twisted pair cable.  The same chip can receive this signal and convert it back into the original unbalanced data.

I've tested over >120m of cat5 but apparently you're good for >1000m