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Page Revision: 2020/07/23 20:04
This article describes the design of a electronics debugging tool for electronic circuits.
It's main purpose is to give a graphical representation of the impedance at a node of the circuit, similar to a commercial product, the Huntron Tracker.
The tool allows for very fast fault finding in electronic circuits, especially when a known good circuit is available, so graphs can be compared.
If there is no known good circuit is available, still comparison can be made to similar nodes in the same circuit, and differences point to the culprit.
In example microprocessor pins are all similar, if one pin shows a different impedance, there is reason to doubt the microprocessor as being defect.
Creating an impedance graph is based on a very simple principle: apply a voltage to that pin, and measure the current that flows in the pin.
By applying different voltage, the impedance at each voltage can be shown in a graph.
For resistors, Ohms law U=IxR will show a linear relation between voltage and current. A straight line.
For a diode, at positive voltages the impedance will be low, and negative voltage will be high.
This kind of characteristics are visible on the screen of the Backpack Tracker.
The name "Backpack" is from the core building block of this tool: the Micromite Backpack.
The Micromite Backpack is a design of Geoff Graham, and is based around a PIC32 processor that can be programmed in Basic. Information can be found here:
Backpack