Soldering Challenge To Challenge You

[Rick] knew that the blinking, beeping microcontroller kits that are commonly used for educational soldering workshops just would not cut it for a serious combat among SMD reworking professionals. The “Soldering Challenge” he created to fill this gap is a little PCB with eight difficulty levels from large through hole components to the smallest hand solderable SMDs. After assembly, the circuit assesses the skill level of the soldering aspirant based on a built-in scoring system.

soldering_challenge_ongoingThe challenge is meant to be played on a time limit. There are no two same-sized components of different value, so contestants may focus on soldering fast. Little rubber pads on the backside of the board provide for good ground contact in the curves. After the starting signal, you will be confronted with a few through hole resistors, a capacitor, different LEDs and a DIP-8 IC. Here it’s all about the speed and efficiency as you tackle a track full of bends and cut-off resistor legs. Over the course of the challenge, the components get smaller and smaller, until you finally reach the 0603 level, with a tiny SC-85 MOS-FET and a TSSOP 555 timer at the finishing line.
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Which resistor values should you order for all circumstances?

A hard drive crash, and some other happenings that aren’t entirely clear to us, led [Devbisme] to put in a parts order. As he wanted to make the most of his shipping costs, he decided to fill out the order with parts that he’ll use eventually. He’s been working with surface mount designs and wanted to move from using resistors with 0805 packages to the 0603. Having nothing on hand, he devised a way to account for almost all standard values with the fewest number of different resistors.

That’s a mouthful, but what he actually did was figure out what combinations of resistors can best be wired in parallel to achieve a different standard resistance value. This way, if he doesn’t have a specific value he can solder one 0603 surface mount resistor on top of another one to get there. He ended up writing a Python program to best calculate this set of values. It came up with a set that lets him synthesize 159 of the 168 standard resistor values within +/- 4% using just 19 actual resistor values. His method requires anywhere from one to three resistors to get to each value. Soldering three 0603 packages on top of each other might not be the most fun, but it makes for easy parts inventory management.