Modulated Square Wave

Modulated Square Wave







A Modulated Square Wave is a series of High/Low signals repeated rapidly.

Like the switched signals (B+, B-) the square wave has only two voltage levels.

A high level and a low level.

A modulated square wave has 3 characteristics that can be modified to vary the signal:
- Frequency
- Pulse Width
- Duty Cycle

Frequency
The frequency of a modulated square wave signal is the number of complete cycles or pulses that occur in one second. This number of cycles or frequency is expressed in Hertz (Hz). 1 Hz - 1 complete cycle per second.












An output function may use a fixed or varied frequency.

Typical Application of Fixed and Varied Frequency

Fixed Throttle command DME to EDK/MDK
Idle motor controls from DME
DKT signal from DME


NOTE: Most fixed frequencies are 100 Hz.


Varied Hall effect crank sensor
Hall effect wheel speed sensor
Hall effect camshaft sensor

Pulse Width

Pulse Width:

The Pulse Width of a square wave is the length of time one pulse is ON. Vehicle systems may use fixed or varied ON times or pulse width. Pulse width is expressed in milliseconds (ms).

Duty Cycle

Duty Cycle:

The Duty Cycle of a square wave is the ratio of ON time to OFF time for one cycle. Duty cycle is expressed in %. Vehicle systems use both fixed duty cycle signals and variable duty cycle signals.

Time

1 second 1000 milliseconds (ms)
1/2 second = 500 milliseconds
1/4 second = 250 milliseconds
1/10 second = 100 milliseconds
1/100 second = 10 milliseconds
1/1000 second = 1 millisecond