Sunday, January 15, 2012

SMT Training Course

Finished kit with cover over PC board.
Just finished up the Elenco Surface Mount Technology Training Course Kit, part number SM-200K. This was my first experience soldering a kit with just surface mount components, turned into an interesting process.

The finished kit is called a Decision Maker, by pushing a switch six LED's blink in sequence and a buzzer sounds until one LED remains on.

Theory of Operation:

6 LED's are driven by a decimal counter and two oscillators. One oscillator drives the decimal counter and the other drives a buzzer. Two timers control the counter and the oscillators. The decade counter IC 4017 is a 5 stage divide by 10 counter. This IC has 10 outputs and one clear input. Only one out of ten outputs are high, the other nine are low. Every time a pulse is fed to the clock input, output 1 will go low and output 2 will go high. Each clock pulse will move the output one position. When an LED is connected the the output, it will light when output is high. When clock is on LED's flash ON and OFF with the speed on the clock. When the clock stops only one LED remains lit.

This kit uses two oscillators, one produces a frequency of about 200 hertz, and the other is about 20 hertz.The 4011 IC contains four two input NAND gates. Two of these NAND gates are needed to form an oscillator. Both ICs act as inverters, when input is low, output is high. One oscillator controls LED's depending on if pin 1 is high the circuit will oscillate, when pin 1 is brought low, the circuit stops oscillating. The second oscillator produces the buzzer sound.

Parts List:
8 resistors, 4 capacitors, 2 diodes and IC's, 6 LED's,
PC board, buzzer, switch, battery snap.

Construction Notes:
  • Use plenty of lighting, these SMT devices are super small, TINY.
  • I also use a magnifier light with arm attachment to my desk.
  • One device is lined up over pads use clear tape to hold one side down, this make these devices super easy to solder. Never thought I would say that with surface mount.
  • Kit includes four resistors and a spot on board to place them on for practice.
  • Small soldering iron tip is helpful.
  • Funny the time is took me to line up the small devices compaired to your standard leaded parts.
  • Ultra short capacitor leads, no clipping with this kit!
  • Lay off the pre-building coffee drink, steady hands help here.

PC board with components mounted.
Smoke Test:

The LED's lit up the first time but no sound from the buzzer. I double checked both IC's and notice one lead did not have a solid connection to PC board, resoldered and buzzer sounded perfect.

This is a good kit to get your feet wet and build confidence working with surface mount devices.

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