Speaker tick generator #2 (for polarity testing)

A recent purchase of an inexpensive ($6) speaker polarity tester prompted a need for a stand alone driver for speakers.

Above, the tester has a microphone that senses the polarity of the pressure wave and indicates with one of two LEDs.

The tester comes with a CD containing a file that can be used to provide the test signal on a complete system with CD player, but there is a need for a stand alone driver for testing bare speakers or speaker units.

Speaker tick generator (for polarity testing) described a stand alone test pulse generator based on re-purposing a brushless DC motor controller (ESC, used for RC models).

This article describes  a simple tick generator using a inexpensive 8051 type MCU (STC15F104E) and a H-bridge IC (TC427).

Above, the prototype was build on a small piece of Veroboard. DC input of 6-15V is applied to the 2.1×5.5mm DC jack, and speaker output is on the screw terminals (nearest to DC jack is -ve).

NOTE: the speaker wires must NOT be connected to either DC + or -.

Above is the copper side of the Veroboard.

Above, the assembly served with heat shrink tube to protect it in use.

Above is a shot of the voltage developed across one of the 1Ω current limiting resistors, so it is speaker current scaled 1A/V. The current waveform will be different for different speakers, depending on nominal impedance, frequency range, crossover networks etc. In this example the peak current is ~400mA

On test, it works a treat. The device sends three +ve pulses followed by one -ve pulse, and repeats the sequence.

Above, the schematic.