Comments on: LED Curve Tracer: Hardware

By: Red LEDs: Current vs. Voltage Sorting « The Smell of Molten Projects in the Morning

Wed, 26 Dec 2012 12:14:54 +0000

[...] ten random red LEDs (taken from the bag of 100 sent halfway around the planet) through the LED Curver Tracer produces this [...]

By: Ed

Ed — Thu, 23 Aug 2012 17:44:53 +0000

a variable current sink using the FET and an OP-AMP

The current feedback loop closes through the Arduino, so it produces about the same net result as the op-amp current loop I used in the MOSFET tester. The whole thing runs at DC, pretty much, so feedback and PWM bandwidth wasn't really an issue. The op amp provided high-side IDS sensing, which meant I could measure the MOSFET VD against ground without correcting for a sense resistor below the source and could drive VGS directly. The much lower LED currents & voltages let me get away with a simpler circuit; I could get the LED drop from the regulator voltage and didn't care about the actual VGS. The IRLZ14 gate doesn't run out of VGS headroom at 100 mA, because the MOSFET hits IDS = 5 A with VGS = 4 V and has a 1-2 V threshold. Here are the curves for VGS from 2 to 10 V in 500 mV steps: Works like a champ!

By: Jason Vandehey (@jasonvandehey)

Jason Vandehey (@jasonvandehey) — Thu, 23 Aug 2012 16:29:55 +0000

I’m just trying to figure out how close your current measurements will be. Do you have an o-scope showing Vgate vs Vsource? (I’m basically wondering about your PWM usage model instead of a variable current sink using the FET and an OP-AMP or something )

By: LED Curve Tracer: Repeatability « The Smell of Molten Projects in the Morning

Mon, 30 Jul 2012 11:47:29 +0000

[...] Measuring the same LED many times should produce the same data every time. Here’s an LED measured ten times in quick succession, with each data point consisting of the average of three ADC conversions: Repeatability – 3 samples [...]

By: LED Curve Tracer: First Light! « The Smell of Molten Projects in the Morning

Thu, 26 Jul 2012 11:40:06 +0000

[...] 5 mm LEDs is generally 20 mA, so 75 mA really puts the screws to them. That notwithstanding, the curve tracer machinery seems to work well [...]

By: LED Curve Tracer: Firmware « The Smell of Molten Projects in the Morning

LED Curve Tracer: Firmware « The Smell of Molten Projects in the Morning — Wed, 25 Jul 2012 11:15:53 +0000

[...] The Smell of Molten Projects in the Morning « LED Curve Tracer: Hardware [...]

By: madbodger

madbodger — Tue, 24 Jul 2012 19:00:18 +0000

Gotta have stuff. However, the curve tracer in that pile is analog, whereas yours can log data which you can then later plot and compare, which will be much more useful for this project.