Introduction: LapTop BreadBoarding

About: Have 30+ years of experiences as a Mixed Signal IC Design Engineer.

Analog Breadboarding on a laptop costs almost nothing, at least on a MacBook Pro.

Step 1: The Interface

Three things make laptop breadboarding convenient.

1)A USB port is designed to provide 5volts at up to 500mA.
2)Sound recording inside PCs is becoming commonplace.
3)A lot of free software is available online.

These three items together with a little interface development can turn a laptop into a full audio bread-board lab environment. Outside of the breadboard, the full interface needed is shown below.

The MacBook provides a line-input stereo audio port in addition to its internal microphones. It looks like this port can only handle signals at the standard audio levels.

USB devices tend to become an open circuit right at the plug interface. The wires in this USB plug were wired to the correct color code. The 5V wire was red and the ground as black. Apparently a 100mA load is a unit load for USB. A 100 Ohm series resistor was added to the 5V line for safety reasons.


Step 2: Optional

If the breadboard looks a little strange, it is because some stack-able jumper-leads were made up to make hooking everything much easier. (Optional)

Step 3: Free Simulation

Outside of the interface, everything else that is needed is either already inside a MacBook Pro or can be downloaded off the web for free.

One excellent program for a Mac is Macspice. This program is completely free and seems to be continually supported. A simple simulation of the breadboard will show what should be expected.

Step 4: First Circuit

A simple triangle/square wave oscillator will be the laptop's first circuit. A low supply current RRIO OpAmp was used in the breadboard. (In this case a LM6132). The output at node "OUT1" will go very close from zero to 5V. But since the audio input port for a MacBook only accepts audio level inputs, R5 and R6 are used to reduce the signal level. Op Amp OPA2 buffers the triangle wave and it needs to be attenuated too.

Step 5: First Simulation

The full simulation code is shown below and yields the following graphs.

Step 6: Free Oscilloscope

The next great free program is called MacCRO X. This is alpha version of a simulated oscilloscope, so everything is not perfect. But when the breadboard is powered up from the USB port and clip leads connect analog signal to the audio input port, the behavior of the breadboard can be viewed real time.

Step 7: ScopeAdjustments

The present version of MacCRO X allows some adjustments in both time and voltage magnitude. The trigger feature does not appear to be working well. But there is a button to freeze the scope trace.

Step 8: XY Display

This is a dual trace oscilloscope which is powerful.

Step 9: Run Both

For those of us who believe in trusting nothing, now its possible to sanity check real time analog waveforms with simulations on the same laptop, all at the same time.

Step 10: Free Wave Capture

The present version of MacCRO X appears to neither trigger well nor store waveforms in a convenient manner. That is where another great free program comes in.

While there are many programs that can record audio signals, Audacity appears to be the best.

Step 11: The Power of Dual Trace

Having the ability to capture a large amount of dual trace data is very powerful when it come to debugging any hardware. The dual trace feature makes it much easier to hunt down cause and effect relationships. While MacCRO X is a long way from having the triggering power of a typical oscilloscope, Audacity can capture and display a large amount of data which can then be looked over to find a particular event.

Step 12: Who Needs a Soldering Iron?

Given the present state of both the hardware and software available on a MacBook Pro, it looks like getting some hands-on analog experience might be getting much easier in the future. On a 17 inch MacBook, there is a convenient place to scotch tape the breadboard to the laptop where it is stable and out of the way. The use of stack-able jumpers make hook up far faster and easier compared to a soldering iron. It is not obvious things could not get even easier.