Main > Project Announcements
javeryh's Woodgrain Cabaret Copy
PL1:
Time to troubleshoot.
First step, test the LEDs and confirm the polarity.
- Remove power to the panel -- the multimeter will provide power for this test.
- Set your multimeter to diode test.
- Touch the leads to the LED tabs.
-- If the leads are backward, the LED won't light.
-- If you swap leads and the LED still won't light, either the LED is bad or you're on the wrong tabs.
-- If you have the correct polarity and the LED is good, it will light dimly. (make a note of the voltage displalyed on the meter)
Next step is to check if the LED is getting enough voltage to forward bias.
- Set the meter to VDC.
- Restore power to the panel.
- Touch the leads to the LED tabs to test how much voltage is dropped across the LED. Compare that voltage to the voltage during the diode test.
-- If the voltage is lower than during the diode test, you need a lower value current limiting resistor so the LED gets enough voltage to forward bias.
Use a calculator like this one that Zebidee linked earlier.
- Fill in 3 of these 4 values and click on calculate.
* Voltage source = 5v
* Voltage drop from LED = voltage from the diode test
* Current through the LED = usually between 15 and 20 mA
* Resistance = current limiting resistor value
Scott
jennifer:
:)
Zebidee:
Use your multimeter to check voltage out of those IPAC pins.
Make sure you have the polarity of the LEDs right. Long lead/anode to the voltage, short lead/cathode to ground.
Double-check that the GND you are using is connected to the GND on the trackball socket you are getting your 5v from (continuity test). However I expect they are.
Also, ... even though they worked for someone else, 220R for the resistors IMO is marginally viable and might be too high for your particular case. Try 150R if you have them. Even small variations in manufacturing or voltage available from your PC/PSU/IPAC could be enough to make the difference between the LED working in one case and not working in another.
Merry Christmas!!
javeryh:
Thanks everyone... looks like I should have asked for a multimeter for Christmas! I'll try swapping the two wires first - maybe it's just backwards... I hope. I can't believe these 2 stupid buttons are giving me so much trouble...
Zebidee:
You don't need fancy for your first multimeter - I still use the cheap yellow one I got for $10-15 from hardware store over 10 years ago! But a while ago I treated myself with a Fluke 17B+, which is a very nice choice for hobbyists.