Headset control system for operating a microcontroller based device

DETAILED DESCRIPTION OF THE INVENTION In application Ser.
No.
08/920,406 filed Aug.
29, 1997, now U.
S.
Pat.
No.
5,978,689 only two switch states could be detected per wire because only two logic levels, high and low voltage, were designed for.
This limitation is removed with the application of threshold logic.
Threshold logic assigns a different level of voltage (or current) to each switch position so that, there is no theoretical limit to the number of switch states that could be detected per wire.
FIG.
1 shows an example of four-level threshold logic applied to a single wire to detect the switch positions in the headset 10.
The four levels are set by the three threshold voltages, Vr1, Vr2, Vr3, applied respectively to the three comparators, 46A, 46B, 46C.
The comparators detect the voltage on line 55 and provide binary outputs on the microcontroller input lines, 48A, 48B, and 48C.
Any one of the three comparators has a high output whenever the DC input voltage at line 55 is below the reference voltage for that particular comparator, otherwise the output of that particular comparator is zero.
Assuming that the threshold voltages increase in steps such that, Vrl<Vr2<Vr3, the output states of the three comparators are related to the voltage V55 at line 55 as follows.

TABLE 1
Level V55 48A 48B 48C
1 0 < V55 < Vr1 1 1 1
2 Vr1 < V55 < Vr2 0 1 1
3 Vr2 < V55 < Vr3 0 0 1
4 Vr3 < V55 0 0 0
The headset contains a three-position push button switch 105 and a two-position boom switch 12.
The circuit has been designed such that each combination of switch positions results in a DC voltage at line 55 corresponding to one of the four levels listed above.
An example of circuit values along with logic levels is listed in Table 2 below.
First column shows the switch 12 position in upper boom position where the switch is connected to the speaker and in lower position where the switch is down in front of the mouth position