LED characteristics practical.

Discussion in 'General Forum Tutorials' started by Prince Brainier, May 21, 2019.

  1. Hi All.

    Just made these for the LED characteristics practical. Frequent problems with old ones which were just an LED and a resistor in series. If reverse connected the LED would sometimes POP and need replacing. As the voltage monitoring had to be done across the two components the resistor would swing the results. If we let them have access to the LED terminals there was the chance they would connect directly and cook up the LED. Here the LED is protected from reverse voltage by a 1N4007 reverse connected. The LED is connected by two 620R resistors so one can be used to monitor the volts directly across the LED. 620R compared to the 10meg of a DMM is negligible.
    I've used Toolstation 15A connectors that accept banana plugs well. This saves on buying sockets and of course keeps the profile low as the connectors are along the mounting plate, not through it. The base is laser cut acrylic from our DT dept and all is held in place with hot glue. No reason why MDF or even card might not be used if money is tight. I'm convinced that with zip ties and hot glue I could make a car. LED sets (1).jpg LED sets (2).jpg
  2. Wonderful stuff, a very logical way to overcome some common problems encountered with Bods and LEDs! (And some teachers).
    Highly commended!
  3. Nick Mitchener

    Nick Mitchener COMMITTEE

    On my long list of jobs is rebuilding the kits I made that yr12 trashed, I will be fitting protective diodes and resistors in series with the voltmeter sockets. Our lot put 12 volts into the voltmeter sockets then when that LED didn't work switched through the other 5 blowing each in turn!

    I like the idea of using strip connectors as 4mm sockets, will find applications for that!
  4. I got fed up with constant breakages, one group even tried using AC after they destroyed all the LEDs.
    Now all kits are in ABS boxes with bridge rectifiers, voltage regulators etc. So AC or DC up to 32V will still produce a normal safe display as intended.
    Power is via a 12V wall-wart so all they need is ammeters and voltmeters.
  5. Nick Mitchener

    Nick Mitchener COMMITTEE

    We only allow students up to a 13V supply. I have taken all the planck's constant kit home to repair over the summer, will fit schottky diodes for reverse polarity protection and 1000 ohm resistors in series with the voltmeter sockets, then replace any damaged LEDs. I usually give them strips of four D cells but the teacher permitted them to use mains power supplies. Sadly in that lab the mains supplies are not on a trolley so I can't wheel them out.