Data Logging in the Picoampere Range

You probably know that to transfer the most energy between a source and a load their impedance needs to match. That’s why a ham radio transmitter needs a 50 ohm antenna (at least, usually). The transmitter is 50 ohms and you want a match. Some test equipment matches impedance, but for multimeters, oscilloscopes and a lot of other gear, the instrument just presents a very large impedance. As long as it is much larger than the measured circuit’s impedance, the effect will be small.

With today’s MOSFET instrumentation amplifiers, it isn’t uncommon to see very high input impedances.  However, you sometimes run into something that has a low input Z and that can cause issues if you don’t account for them. On the other hand, where some people see issues, others see opportunities.

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VirtualBench Tear Down

What do you get when you cross a mixed-signal oscilloscope, a function generator, a multimeter, a power supply, and some programmable digital I/O in a box? Sounds like the set up to a very geeky joke, but it is actually National Instrument’s VirtualBench product. [Shahriar] has one and wanted to know what was inside, so he did a tear down.

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Breadboards Go to Pot

Solderless breadboards are great for ICs and discrete components like resistors, capacitors, and transistors (at least the through hole kind). They aren’t so good at holding big components like potentiometers. Sure, you can jam trimmers in maybe. You can also solder leads to a pot, but that’s not pretty and tend to pull out when handled. [PaulStoffregen] got tired of it, so he put together some good looking PC boards that mount a 6mm shaft pot securely to a breadboard.

[Paul] noticed that having delicate or knobless adjustments on a breadboard inhibited people from playing with demo circuits. The new set up invites people to make adjustments. The pictures and video show an early version with six pins, but [Paul] added two more pins on the recent batch to increase the grip of the breadboard.

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Hot-Wire CNC Foam Cutter From E Waste

A couple of old DVD ROM drives and a compact photo printer is fairly standard fare at the thrift store, but what do you do with them? Hack them up to make a CNC foam cutter of course!

[Jonah] started with a couple LITE-ON brand DVD RW drives, which use stepper motors instead of plain old DC motors. This is a huge score since steppers make accurate positioning possible. With the internal frames removed, threaded rod and nuts were used to hold the two units parallel to each other forming the Z axis.

The feed mechanism from a Canon compact photo printer was then bolted onto the bottom to form the Y axis. Add a bit of nichrome wire for the cutting element (this can be found in old hair dryers) onto where the laser assembly of the DVD rom once lived, and you have the mechanics done.

Control is handled by an Arduino and some easy-driver modules to interface with the steppers. G-Code is generated by CamBam, which handles various cad files, or has its own geometry editor.

This is a fantastic way to get your feet wet in several ways; Cracking things open to harvest parts, driving steppers with simple micocontrollers, modeling and generating g-code, etc. The one issue we see with this build is a chicken-or-egg problem since you need to have a cube of foam cut down to somewhat strict dimensions before it will fit in this cutter. But we suppose that is really just an iterative design problem.

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Building an Atomic Force Microscope on the Cheap!

LEGO2NANO, are building an open hardware AFM (Atomic Force Microscope).

AFMs are a kind of probe microscope. Unlike an optical microscope, a probe is used to “feel” the topology of a surface. An atomic force microscope uses a flexible cantilever with a nanometer scale tip on the end. As the tip scans across the surface it will be deflected by its interaction with the surface. A laser spot is usually reflected off the back of the cantilever, and captured by a photodiode array. The angle of the reflected beam, and therefore which photodiodes are excited lets you know how much the cantilever was deflected by the surface.

One of the challenges of building an AFM is developing an actuator that can move with nanoscale precision. We recently reported on [Dan Berard]s awesome capacitor actuator, and have previously reported on his STM build which uses a piezo buzzer. LEGO2NANO are experimenting with a number of different configurations, including using Piezo buzzers, but in a different configuration to [Dan]s system.

The LEGO2NANO project runs as a yearly summer school to encourage high school students to take part in the ambitious task of building an AFM for a few hundred dollars (commercial instruments cost about 100,000USD). While the project isn’t yet complete, whatever the outcome the students have clearly learned a lot, and gained an exciting insight into this cutting edge microscopy technique.

Monsieur Adaptateur: Jacques of all Connector Trades

It seems that any time you have a circuit on the bench, there’s wires. Lots of wires. If you are working on something new, it is a good bet that some of those wires are clipped to other wires using some field expedient, especially the power wires. We often have an alligator clip awkwardly grabbing the shell of a BNC. [Felicitus] got tired of this, so he created Monsieur Adaptateur, a breakout board that has common connectors you’ll need when working on a prototype.

What kind of connectors?mafull

  • DC Jack 2.1mm
  • 2mm Jacks
  • 4mm Jacks
  • BNC Connector
  • Terminal Block
  • Scope probe connector
  • Standard 6 pin 0.1″ female header
  • Standard 6 pin 0.1″ male header
  • 4.75 and 6.3mm blade connectors

The dual conductor items (like the 2.1mm jack and the BNC) connect to both sides of the board. The other connectors are in pairs. The idea is you can connect, for example, a BNC cable from a signal generator to some jumper wires on the male header, connect the scope to the scope probe connector, and still have the banana jacks to hook up, say, a digital meter.

No one would say this is going to change the world, but this is one of those things that is simple, but very useful. The plans are all on Github, and obviously you could adapt it with connectors that make sense for your specific situation.

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A Tale of Two Browser PCB Tools

We live in a golden age of free Electronic Design Automation (EDA) tools. It wasn’t that long ago that an engineering workstation was an expensive piece of hardware running very expensive software that typically had annual fees. Now, you can go to your local electronics store and buy a PC that would shame that old workstation and download plenty of software to design schematics, simulate circuits, program devices, and lay out PCBs.

The only problem with a lot of this free software is it runs on Windows. I do sometimes run Windows, but I most often use Linux, so there is a certain attractiveness to a new breed of tools that run in the Web browser. In particular, I wanted to look briefly at two Web-based EDA tools: EasyEDA and MeowCAD. Both offer similar features: draw a schematic, populate a PCB, and download manufacturing files (that is, Gerber files). EasyEDA also offers SPICE simulation.

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