I am here putting together SMT Kit for practice. Instructions which came with the kit are horrible.
I have basically two problems.
On the 4017 and 555 there is no notch or dot to figure out the way they should be installed. I have looked at them with magnifying glass and nothing really comes out. What you gurus do in this situation.
I am not able to figure out kathode/anode of the SMT led. One corner of the LED is cut. So that probably is the key but which one?
Thank you beforehand for any help.
Best Regards Kari Laine
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PIC - ARM - Microcontrollers - I2C - SPI
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http://www.byvac.com
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I don't know. In DIP packages, sometimes there was something underneath to indicate which side was which.
I've always hooked LEDs up to a 9v battery with a suitable dropping resistor. One way will light up the LED. It's a way to reuse weak batteries that have seen use in some device. Way back when I started doing this, it was pretty important since a lot of the cheap LEDs were lousy (so you wanted to test the LED) and you couldn't always be sure they were packaged right. LEDs are easy since they light up when voltage is applied properly.
There is nothing underneath either. I have stared the bug so that my eyes hurt. I am thinking that someone has sold substandard components and this Kit manufacturer has went for cheap price or something... I just had a second look and there is no notch or dot. I am going to test it so that the end were the text is, is the end with 1.
Simple ! Thanks !
Best Regards Kari
--
PIC - ARM - Microcontrollers - I2C - SPI
Keypads - USB-RS232 - USB-I2C - Accessories
http://www.byvac.com
I am just a happy customer
The pin 1 side of most SMT packages is indicated by a beveled edge, or a molded dot, or sometimes a clipped corner. The beveled edge can be... subtle.
One convention on LEDs is that the cathode(-) has the shorter wire. SMT, not so much. Since your source of LEDs is probably not printed on the package, you can't look it up in the data catalog, alas, in most 'got-a-bag-of-'em' situations. A DMM with 'diode check' will usually light 'em up with a safe current. There's usually a band or dot or bevel or somesuch next to the cathode. If you see an arrow, it points to the cathode.
--- If you have a variable power supply, adjust its output to 0V, connect one end of a 1000 ohm resistor to the + output, and connect the other end of the resistor and the - side of the supply to the LED.
Then, slowly increase the output of the supply until the LED starts to light up.
If you get to 4V or so and the LED doesn't light up, reduce the output voltage to 0V, reverse the connections to the LED, and try again.
In either case, when the LED lights up the lead connected to the resistor will be the anode.
If you don't have a variable power supply you can use a 9V battery, but you have to be careful in order not to destroy the LED.
Please have a look at the top of page 17. Notice how the plastic over pins 1 through 4 has a 45 degree edge instead of the 90 edge over pins 5 through 8?
Your multimeter 'continuity' beeper can help here:
Look for a notch-like mark in the end with Pin 1 and highest number pin, or a dot-like mark in the corner towards pin 1. These marks may be subtle and may require good or tricky lighting.
Otherwise, orient the IC to have printing on it rightside-up. In such orientation, pin 1 is lower-left and the highest number pin is upper-left.
Use a 3 to 5 volt power supply with a 220 ohm resistor (any wattage and tolerance up to +/- 20%) in series - test the LED to see which way lights it. I have yet to blow an LED by applying 5.5 or even 6.0 volts in the wrong direction through a resistor 100 ohms or more. Heck, I have yet to blow an LED by applying a 9-volt battery to an LED with incorrect polarity through a resistor of 220 ohms or more, though I am aware that many LEDs are only rated to survive reverse voltage up to 5 volts.
Two things to keep in mind here:
1) Many LEDs cannot withstand "full rated power" in "reverse breakdown mode"
2) Most UV, violet, blue, bluish-green, non-yellowish-green, white, pink, and purple LEDs experience damage if "reverse breakdown" occurs, no matter how little current, power or energy goes into actual breakdown of the LED chip itself.
Otherwise, find its datasheet and see if the datasheet shows polarity markings. If DigiKey sells this LED, chances are at least 99.5% that their website links to its datasheet. Mostly the same story with other major "true" distributors that sell the actual product.
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