Smart Patrol!

This article presents a very elegant robotic end-effector built using coffee grounds

It works by jamming a membrane filled with granular material (coffee grounds in this case) onto the target object. Air is then vacuumed from the membrane, resulting in a secure grip on the object.

Those of you that grew up in the 90’s may remember Vac-Man, an action figure that worked using the same principle (I believe he was the arch nemesis of Stretch Armstrong)

Neato!

Recently I was asked how one would drive a (relatively) high current load with a microcontroller. Since microcontroller output pins are not capable of directly driving much current, some external components must be used. This can be accomplished by our friend, the MOSFET.

A MOSFET is a type of transistor that can be used as an electrically controlled switch, essentially allowing a low current/voltage signal to control a high load. They act like relays, in that a control signal opens or closes the “switch”. MOSFETs can be switched much faster than a relay, making them useful for motor speed control, audio etc.

Switching is accomplished by applying a voltage to a gate input. The voltage required in order to saturate the gate (to turn it on) varies from MOSFET to MOSFET, and most are over 5 volts. MOSFETs with a higher gate voltage will not be able to be turned on by a lowly microcontroller signal, or will operate inefficiently (and possibly burn up)! Driver ICs and small transistors can be used to switch these devices, but selecting a logic level MOSFET removes this constraint.

An IRL520 MOSFET is used in the diagram above to drive an inductive load, in this case a solenoid. The gate signal of this device can be driven by a voltage of 4-5 volts. When this voltage is applied, current is allowed to flow from the source to the drain pins, which drives the solenoid.

Now one last caveat, our inductive load suffers from a phenomenon called “flyback”. When the power supply to the inductive load is cut, a certain amount of magnetic energy remains in its windings. The inductor tries to resist the change in voltage with its stored magnetic energy, resulting in a “flyback” current. This current needs somewhere to go or else it will be forced into the deactivated MOSFET. This will degrade the MOSFET and lead to failure.

To mitigate this, a 1N4001 diode is used to direct the flyback currents back through the inductor. The currents are now directed away from the drain and allowed to dissipate in the inductor, which keeps our MOSFET happy.

Howdy folks,

This is the first post on my tech blog. I will be making frequent posts about robots, electronics, cool hobbies, and other nerd stuff. Posts will focus on my own work as well as other sites that I find interesting or useful.

The goal of this site is to promote knowledge sharing amongst hobbyists and professionals alike. I will avoid politics, general whining, and useless mass media. If you are interested in that sort of thing, there is always TV.

I encourage you to add comments and questions on my posts, I will reply as often as possible.

Cheers!
Chris