ACCESSORY DETECTION BY OSCILLATION

Publishing Venue

Motorola

Related People

Abstract

Subscriber radios have a need to scan for multi- ple different accessories at their accessory connec- tor. Traditionally, options are detected using a binary coding scheme shown below in Figure 1. Each acces- sory is assigned a different combination of Rl and R2 values so that a unique binary code is presented Subscriber Radio to the microcomputer. This requires a large number of dedicated I/O pins and microprocessor lines for the simple process of determining which accessory is connected. Such dedication of resources is waste- ful and expensive for subscriber radio products.

Technical Developments

ACCESSORY DETECTION BY OSCILLATION

by Dave Mills

  Subscriber radios have a need to scan for multi- ple different accessories at their accessory connec- tor. Traditionally, options are detected using a binary coding scheme shown below in Figure 1. Each acces- sory is assigned a different combination of Rl and R2 values so that a unique binary code is presented

Subscriber Radio

to the microcomputer. This requires a large number of dedicated I/O pins and microprocessor lines for the simple process of determining which accessory is connected. Such dedication of resources is waste- ful and expensive for subscriber radio products.

Accessory

Rl R2

No option not used not used Option 1 10K not used Option 2 not used 10K Option 3 10K 10K

3 ^Rl

I?2

f

Microprocessor accessory connector *

Fig. 1 Traditional accessory detection

  A simple way to solve this problem involves using the line. Since each accessory produces a different a resistor divider that provides a different voltage for voltage the microcomputer can determine which each accessory This one line is then connected to accessory is attached (see Figure 2 next page). The an A/D port on the microcomputer. This allows the problem with this is that GE has a patent on it. microcomputer to directly measure the voltage on

0 Motorola. 1°C. 1996 86 August 1996

Technical Developments

Subscriber Radio

Accessory

Rl Vl

No option n/a 5V Opti...