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In addition to making shortcuts for our customers, here at SparkFun we are also constantly making shortcuts for ourselves. Whether it's in our finance department or on the production floor, we are always looking to improve our systems and make our jobs easier.
This project originated from a task in our kitting department. Each time we make the Simon Says - Through-Hole Soldering Kit, we need to make sure that each kit gets four unique LEDs: red, green, blue and yellow. When these LEDs are not lit up, they are clear, and so it is impossible to tell their color. In the past, we have used a battery or multimeter to quickly light up the LEDs and verify the colors. This is pretty quick, but it requires getting the polarity correct and sometimes it can be difficult to touch each wire to each LED leg.
As the quality control manager here at Sparkfun, I have recently spent more time over in the kitting department. I've been helping them out with any ideas I may have for QC and system improvements. After seeing the pain of this LED testing procedure a few times, I thought, "How about a set of tweezers, a pro micro and some fast-switching?"
Cut and strip the two wires off of the tweezers. Twist each end to help avoid fraying.
Solder to pins 6 and 7 on the Arduino Pro Mini.
*A quick note* Wait until you're done soldering to put the batteries in place. It's always a good idea to do soldering without any power involved. You don't want to accidentally short out your batteries while soldering.
Cut and strip the two wires off of the battery holder.
The red wire goes into "RAW"
The black wire goes into "GND"
Solder the Buzzer to pins 10 and 13. You'll notice that the distance of these two header holes is just about right for the buzzer. This is why I chose 'em! The polarity for this does not matter. It will make a buzz either way.
Now that you're done soldering, it is safe(r) to plug in your batteries. Depending on how you program your pro mini, you may or may not need to turn it on.
Click HERE to download the code. You will also need to download the Arduino Software, if you haven't already.
This code will simply toggle the "tweezer lines", but it will also play a melody when you first turn it on and sound an alarm when you've left them on for over an hour. If you'd like to change the alarm time, try lowering or raising the number in alarm if statement:
// FAST SWITCHING of the tweezer lines (pins D6 and D7)
// Set the tweezer probe in one direction (HIGH/LOW) to turn on an LED.
// If LED "+" side is touching tweezer probe D6, and LED "-" is touching tweezer probe D7, it will light up.
digitalWrite(6, HIGH); // write tweezer probe D6 HIGH.
digitalWrite(7, LOW); // write tweezer probe D7 LOW.
// Set the tweezer probe in the oposite direction (LOW/HIGH), to turn on LEDs in oposite polarity.
digitalWrite(6, LOW); // write tweezer probe D6 LOW.
digitalWrite(7, HIGH); // write tweezer probe D6 HIGH.
// ALARM feature
// Check to see how long the arduino has been running
time = millis(); // millis() will return an unsigned long integer that increases as time goes on.
// It will tell us how long the arduino has been running since it was furst turned on.
// Decide if alarm should sound
if(time > 3600000) // if it's been over 1 hour (3600000), start alarming.
for(int i = 0; i<7;i++)
You can change the 3600000 to 1800000, if you'd like it to alarm after 30 minutes.
First, clean off your solder joints with some rubbing alcohol. Even a quick wipe with a tissue or paper towel will do just fine to clean up your board.
Using some strips of double-sided sticky tape, attach your pro mini and battery holder to the tweezers.
Make sure to keep the battery ON/FF switch accessible.
It's also not a bad idea to keep the programming lines accessible. Sometime down the road, you may want to tweak the code a bit - maybe add your own melody!
For gear that's going to be handled a ton, I always like to add a bit of hot glue to each wire solder connection. This acts like a strain relief on the connection and usually helps it live a little longer.
Congratulations, you have completed your very own set of fast-switching tweezers! Go ahead an light up any bare LED you like. And don't worry about polarity :)