Comments on: Project Idea: LED Calculator http://www.neufeld.newton.ks.us/electronics/?p=216 Sun, 08 Dec 2024 17:19:24 -0600 hourly 1 http://wordpress.org/?v=3.1.3 By: Conrad Braam http://www.neufeld.newton.ks.us/electronics/?p=216&cpage=1#comment-23089 Conrad Braam Fri, 24 Apr 2009 15:38:14 +0000 http://www.neufeld.newton.ks.us/electronics/?p=216#comment-23089 Hmmmm, I am thinking a microcontroller with a A/D can do what you want, is it evil to change the User-interface to use 2 buttons instead, one for brighter, and another for dimmer? And then only have one LED socket? The circuit can start in "dimmest" first, and then use the 2 buttons to adjust brightness up/down as desired. When the brightness buttons are left un-touched for say 5 seconds, the microcontroller can spit out your answer directly to your USB port, serial port connected to your PC and display there. But that's not simple enough, the microcontroller should give a read-out on the LED under test or via 8 LEDs arranged in a binary-code? I hate to complicate it with a 7-segment display, because you need at least 3 digits, so maybe a USB port to your PC is the solution? The big advantage to a solution that runs off your USB port is that we can give resistor values for any power supply in a tiny GUI. Hmmmm, I am thinking a microcontroller with a A/D can do what you want, is it evil to change the User-interface to use 2 buttons instead, one for brighter, and another for dimmer? And then only have one LED socket?
The circuit can start in “dimmest” first, and then use the 2 buttons to adjust brightness up/down as desired.
When the brightness buttons are left un-touched for say 5 seconds, the microcontroller can spit out your answer directly to your USB port, serial port connected to your PC and display there.
But that’s not simple enough, the microcontroller should give a read-out on the LED under test or via 8 LEDs arranged in a binary-code? I hate to complicate it with a 7-segment display, because you need at least 3 digits, so maybe a USB port to your PC is the solution? The big advantage to a solution that runs off your USB port is that we can give resistor values for any power supply in a tiny GUI.

]]> By: David Fowler http://www.neufeld.newton.ks.us/electronics/?p=216&cpage=1#comment-21381 David Fowler Sun, 03 Feb 2008 07:23:17 +0000 http://www.neufeld.newton.ks.us/electronics/?p=216#comment-21381 Keith, You might also add a photo detector to measure the brightness of the LED with the uC and get a measure of relative brightness. Along with voltage drop and current you could find efficency. One issue would be calibrating the photo detector. I would like to know of a good way to do this. Perhaps a diode with known specs would work for this. You could also plot light output vrs current and find the efficent sweet spot for the LED. Keith,

You might also add a photo detector to measure the brightness of the LED with the uC and get a measure of relative brightness. Along with voltage drop and current you could find efficency. One issue would be calibrating the photo detector. I would like to know of a good way to do this. Perhaps a diode with known specs would work for this. You could also plot light output vrs current and find the efficent sweet spot for the LED.

]]> By: David Fowler http://www.neufeld.newton.ks.us/electronics/?p=216&cpage=1#comment-21380 David Fowler Sun, 03 Feb 2008 06:21:52 +0000 http://www.neufeld.newton.ks.us/electronics/?p=216#comment-21380 Keith, Instead of using a uC you could use a bench DVM as a display. Output the current as a voltage that is read by the DVM. The tester circuit could be very simple, just a small box with connections for the LEDs and a knob. The current could be output 1:1 (1 volt=1 amp) and a switch could select between current and diode voltage drop. Keith,

Instead of using a uC you could use a bench DVM as a display. Output the current as a voltage that is read by the DVM. The tester circuit could be very simple, just a small box with connections for the LEDs and a knob. The current could be output 1:1 (1 volt=1 amp) and a switch could select between current and diode voltage drop.

]]> By: David Fowler http://www.neufeld.newton.ks.us/electronics/?p=216&cpage=1#comment-21379 David Fowler Sun, 03 Feb 2008 06:18:52 +0000 http://www.neufeld.newton.ks.us/electronics/?p=216#comment-21379 Keith, Consider a current source made with a transistor. The uC could read the current applied and the voltage drop on the LED. With these two parameters you could calculate the serries resistor needed given the supply voltage. You could have the uC display the resistor value as the pot is adjusted if you knew what the desired supply was. I show a current source made from two transistors at the following link. You could use a simpler version for this applicaiton. http://www.uchobby.com/index.php/2006/11/12/current-limited-pc-power/ Keith,

Consider a current source made with a transistor. The uC could read the current applied and the voltage drop on the LED. With these two parameters you could calculate the serries resistor needed given the supply voltage. You could have the uC display the resistor value as the pot is adjusted if you knew what the desired supply was.

I show a current source made from two transistors at the following link. You could use a simpler version for this applicaiton.
http://www.uchobby.com/index.php/2006/11/12/current-limited-pc-power/

]]> By: Forrest M. Mims III http://www.neufeld.newton.ks.us/electronics/?p=216&cpage=1#comment-21374 Forrest M. Mims III Sat, 02 Feb 2008 21:04:32 +0000 http://www.neufeld.newton.ks.us/electronics/?p=216#comment-21374 Keith, While your LED tester is a great project as-is, the goals for the advanced unit are even better. I agree with you about using 9 volts. Please consider proposing an article about this to NUTS AND VOLTS magazine. If they are not interested, I am and will be glad to publish the plans for your present unit in THE CITIZEN SCIENTIST ( www.sas.org/tcs ) which I edit. Forrest M. Mims III Keith,

While your LED tester is a great project as-is, the goals for the advanced unit are even better. I agree with you about using 9 volts.

Please consider proposing an article about this to NUTS AND VOLTS magazine. If they are not interested, I am and will be glad to publish the plans for your present unit in THE CITIZEN SCIENTIST ( http://www.sas.org/tcs ) which I edit.

Forrest M. Mims III

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