On 7/20/05, Dominic Stratten wrote: > > > -----Original Message----- > From: piclist-bounces@MIT.EDU [mailto:piclist-bounces@MIT.EDU] On Behalf Of > Russell McMahon > Sent: 20 July 2005 10:14 > To: PIC List > Subject: [EE] NZ only - Cheap useful multimeter > > > > WARNING: When measuring current on ANY cheapo meter measure the > voltage drop across the meter when operating. This may surprise you. > Resistances of 10 to 20 ohms on eg 200 mA range are not unknown and can > cause major problems in some cases if not accounted for. > > > RM > > > Very very sound advice !!!! > > I set up a meter in series with a Luxeon LED and adjusted the voltage until > I had an exact 250ma setting on the PSU. > > Removed the meter and connected it straight to the PSU and poooof !!! 500ma > straight through the LED which after a few seconds of glowing nice and > brightly promply overheated and self destructed. If you'll spend just a little more time and build a constant current supply, this never hapened. It looks like you've used a small voltage power supply and a resistor in series with your led. Large current white or blue leds or even laser diodes must never be supplied like you've done. best wishes for the future, Vasile > > It wasn't a cheap meter either :-( > > Dom > > -- > No virus found in this outgoing message. > Checked by AVG Anti-Virus. > Version: 7.0.323 / Virus Database: 267.9.2/52 - Release Date: 19/07/2005 > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist