I am planning to build a few guitar pedals, and plan to use Rod Elliott's information on DIY Vactrols for switching (Project 145), so I thought I should try the LEDs in my parts bin to find the best.
Test setup not very elaborate, just a 3.3K resistor to limit current from a 17.9VDC supply. Single test samples only (I wasn't looking to generate design data). I used a 4-1/2 meter, but it's a no name brand, so I don't consider it terribly accurate.
cheap red 5mm LED = 316 ohms
white 5mm LED = 170 ohms
white 3mm LED = 147 ohms
Results appear to make sense, LDR resistance is decreasing with decreasing LED lens size, as the 5mm red lens is significantly larger than the 5mm white lens, which in turn is significantly larger than the 3mm white lens.
As for why my measured resistance for the red LED was much lower than Rod Elliott, 2 reasons I can see. I put roughly 5mA through it vs his 3mA. I also think his use of internal glue type heat shrink backfired and put some opacity between LED and LDR.
I'd be interested if anybody has tried this, or any other related schemes, and has something to share.
Test setup not very elaborate, just a 3.3K resistor to limit current from a 17.9VDC supply. Single test samples only (I wasn't looking to generate design data). I used a 4-1/2 meter, but it's a no name brand, so I don't consider it terribly accurate.
cheap red 5mm LED = 316 ohms
white 5mm LED = 170 ohms
white 3mm LED = 147 ohms
Results appear to make sense, LDR resistance is decreasing with decreasing LED lens size, as the 5mm red lens is significantly larger than the 5mm white lens, which in turn is significantly larger than the 3mm white lens.
As for why my measured resistance for the red LED was much lower than Rod Elliott, 2 reasons I can see. I put roughly 5mA through it vs his 3mA. I also think his use of internal glue type heat shrink backfired and put some opacity between LED and LDR.
I'd be interested if anybody has tried this, or any other related schemes, and has something to share.
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