# Ping-Pong Ball Makes Great PID Example

It is a common situation in electronics to have a control loop, that is some sort of feedback that drives the input to a system such as a motor or a heater based upon a sensor to measure something like position or temperature. You’ll have a set point — whatever you want the sensor to read — and your job is to adjust the driving thing to make the sensor read the set point value. This seems easy, right? It does seem that way, but in realitythere’s a lot of nuance to doing it well and that usually involves at least some part of a PID (proportional, integral, derivative) controller. You can bog down in math trying to understand the PID but [Electronoobs] recent video shows a very simple test setup that clearly demonstrates what’s going on with an Arduino, a motor, a distance sensor, and a ping-pong ball. You can see the video below.

Imagine for a moment heating a tank of water as an example. The simple approach would be to turn on the heater and when the water reaches the setpoint, turn the heater off. The problem there is though that you will probably overshoot the target. The proportional part of a PID controller will only turn the heater fully on when the water is way under the target temperature. As the water gets closer to the right temperature, the controller will turn down the input — in this case using PWM. The closer the sensor reads to the setpoint, the lower the system will turn the heater.

# Dropping The Nitrogen Bomb In Science Class

We took Geology in college. It was pretty cool learning about the hardness of different minerals. But there were no explosions involved. We’re not entirely sure what this class is, perhaps Chemistry, maybe Physics, but we want in. [Dr. Roy Lowry] wows the class with a bomb made of liquid nitrogen. The demonstration was part of his lecture at Plymouth University.

A small explosion is cool, but [Roy] knows how to add the wow factor. To make the bomb he filled a one liter plastic bottle about 1/3 of the way with liquid nitrogen. After tightly sealing the cap it was dropped in that garbage can which had a pool of warm water in it. Before quickly running away he and his assistant dumped a few garbage bags of ping-pong balls on top of it all. When the plastic bottle bursts under the pressure of the expanding gas it sends the garbage can about six feet into the air and floods the room with bouncing white balls. See the whole presentation for yourself in the clip after the break and don’t forget the sound so you can catch the oohs and aahs at the end.

Looks like a Hackerspace recruitment tool if we’ve ever seen one.

An 8×8 LED Matrix Game Grows Up:

[Pixel Land] is an iPhone game similar to [Super Mario Brothers] using a virtual array of 8×8 pixels. This wouldn’t normally be interesting, but we’ve actually featured “this” game as an 8×8 LED matrix game.

How to Drill Golf or Ping-Pong Balls:

Drilling golf or ping-pong balls is not easy.  This simple drill press fixture makes that job easier and repeatable. So the next time you want to make lots of diffusers for your LED board, this might be a good device to consider!

The PICkit 2:

If you’ve ever wanted to get into PIC programming, possibly the PICkit 2 would be for you. [Ray] has written a review of his first experiences with setting it up and programming.

Mr Bitey is hungry for resistors!

Is light industrial machinery a hack? It’s a hard thing to define, but if so [Mr. Bitey] would meet the qualifications.  It also meets the qualifications of having a great video, and name, so be sure to check it out!

A [Snap Circuits] Programmable Robot:

The robot pictured above on [Instructables] was built using [Snap Circuits], with parts that literally snap together. A neat concept, this construction set seems to fall somewhere between traditional Legos and push-in breadboards.