Show Posts
Pages: [1] 2 3 ... 15
1  Using Arduino / General Electronics / Re: measuring current with a scope on: September 14, 2014, 08:23:14 pm

I ordered a 5w 0.1ohm current sense resistor.   With scope, hopefully I can see the real current..
2  Using Arduino / General Electronics / Re: measuring current with a scope on: September 13, 2014, 03:14:43 am
It's an LED driver.
3  Using Arduino / General Electronics / Re: measuring current with a scope on: September 13, 2014, 01:25:49 am

I guess with a scope and shunt though I need to be sure the circuits are isolated, no?
The scope does not have battery power.
4  Using Arduino / General Electronics / Re: measuring current with a scope on: September 12, 2014, 05:24:53 pm

I see that current probes are expensive. CTs are cheap though; any disadvantage?  

These AC drivers have weird waveforms, so when I try to measure current the normal way with a DMM, I get weird results.

I wonder if this odd AC driver means my voltage drop is jumping around. If I use a shunt, will the sample rate determine the accuracy of the current measurement? Is a CT more accurate?

5  Using Arduino / General Electronics / measuring current with a scope on: September 12, 2014, 04:46:04 pm

I'd like to measure AC current from a driver with a scope.

It's 12v driver, and desired measuring range is 10mA to about 750mA.

I guess I'd need a current probe, or a current transformer.

My question is in selecting a current transformer.I see many options on Digikey or Mouser, and could use a pointer as to what to select for what I'd like to do.

Can anyone lend any info?
thanks!
6  Using Arduino / General Electronics / Re: power leds driver on: March 10, 2014, 12:07:48 am

Yes, some wasted energy comes with these solutions, but I don't think that's the primary issue that most people care about.
Try to somewhat match V source with the vf times the amount of LEDs to use, and the waste is reduced.
Still better than incandescent.

Having a cheap circuit with some control over current seems a good solution as constant  current drivers are a bit pricey.
7  Using Arduino / General Electronics / Re: power leds driver on: March 08, 2014, 03:49:32 pm
Quote
Replace the fet with an npn ...

What's changing to an NPN do for us?  
8  Using Arduino / General Electronics / power leds driver on: March 06, 2014, 10:51:28 pm

For power LEDs, is there a downside of using a resistor, compared to a constant current driver?
(DC wall wart type supply.)
9  Using Arduino / General Electronics / Re: subjective LED dimming on: March 02, 2014, 01:36:25 pm

I'm interested in dimming very bright LEDs to various levels, and just wondered how effective PWM was at these very short flashes. Normally it would be much longer on-times.
10  Using Arduino / General Electronics / Re: subjective LED dimming on: March 01, 2014, 07:53:53 pm
I'm really thinking of 64th notes at 120bpm. Duration is 32ms.

With 15 pulses in 30ms , it seems like PWM would work to dim.
11  Using Arduino / General Electronics / Re: subjective LED dimming on: March 01, 2014, 06:35:28 pm

The math seems good, but subjectively, does that allow wide dimming?
It seems like it would to me.
12  Using Arduino / General Electronics / subjective LED dimming on: March 01, 2014, 06:23:42 pm

If you have an LED that just illuminates for 30ms or so, would PWMing it still make a perceptible difference in how bright it looks?

I want to have an LED flash just for 30ms, but be dimmable as well.
13  Using Arduino / General Electronics / Re: Ac vs DC on: January 21, 2014, 09:34:22 pm
Slightly less current and power, since some of the voltage is dropped out by the diodes, so less voltage across the resistor means less current.

I know the DC drop is 1.4sh
Is the AC drop different then?
14  Using Arduino / General Electronics / Re: Ac vs DC on: January 20, 2014, 10:09:38 pm
Quote
Does putting a bridge into this change the equation?

Without a capacitor, and with a high enough voltage that the diode forward drop is negligible, no.

With a bridge rectifier, there are two diode drops so about 1.4V is dropped out of the "bottom" of the sine wave. So the power would be less. You could get reasonably close if you take into account the power lost in the diodes.

If you add a smoothing capacitor of sufficient size so that the ripple voltage is tiny compared to the peak voltage, then you are looking at a DC voltage just under Vpk - 1.4V.

So just to clarify my original question...  With either AC or DC input, this complete circuit (with a resistor, an LED and a bridge, and no cap) will use basically about the same overall current, yes?
15  Using Arduino / General Electronics / Re: Ac vs DC on: January 20, 2014, 09:13:16 pm
Quote
Note that for a sinusoidal AC current the power in the resistor varies as a sinuisoid
of twice the frequency, varying between zero and twice the average power.  Average
this over a whole cycle or a long enough time and the power is the same as for DC.

Does putting a bridge into this change the equation?
Pages: [1] 2 3 ... 15