COMPUTER INPUT/OUTPUT INTERFACE SYSTEMS USING OPTICALLY COUPLED ISOLATORS

• US 3,825,896 A
• Filed: 05/01/1972
• Issued: 07/23/1974
• Est. Priority Date: 05/01/1972
• Status: Expired due to Term

• Current Assignee: Robert E. Obenhaus
• Original Assignee: Robert E. Obenhaus
• Inventors: Obenhaus, Robert E.
• Primary Examiner(s): Pitts, Harold I.
• Application Number:
  US05/249,021
• Time in Patent Office: 813 Days
• Field of Search: 340/147R,166EL 250/213A 307/311
• US Class Current: 398/115
• CPC Class Codes: H03K 19/017572 using opto-electronic devices
• CPC Class Codes: H04B 10/802 for isolation, e.g. using optocouplers

Abstract

An input/output interface system for a digital computer utilizes an optically coupled isolator which provides electrical isolation between an external device and the computer. The signal from the external device may be of either A.C. or D.C. form, and the interface system output signal is a logic signal compatible with the I/O logic of the computer. The preferred optically coupled isolator comprises a light emitting diode which is selectively positioned with respect to a photo transistor, such that the diode and photo transistor are physically, and thus electrically, spaced apart but are optically coupled together. A current input signal passing through the light emitting diode causes the diode to radiate, the radiation being received at the base of the photo transistor, which then produces a logic signal indication. In an output interface circuit, the light emitting diode is connected to receive the digital output of the computer and the output of the photo transistor drives a gating circuit which gates power to a load. The interface circuits are particularly adaptable for use in computerized control systems wherein external devices are monitored or controlled.

Claims

1. A circuit for interfacing a digital computer with an external machine, comprising:

a. first resistive means coupled to receive an electrical signal indicative of the status of the external machine;

b. second resistive means coupled to the output of the first resistive means;

c. capacitive means connecting the junction of the first and second resistive means to a reference potential;

d. radiation emissive semiconductor means connected to the output of the second resistive means, responsive to the electrical signal to emit radiation according to the status of the external machine; and

e. a phototransistor optically coupled to the radiation emissive semiconductor means and adapted to produce a logic signal having a logic condition indicative of the status of the external machine.

2. The system of claim 1 wherein said external machine is an on/off switched machine the status of which is indicated by said electrical signal such that a first logic condition of said logic signal indicates that said external machine is on and a second logic condition thereof indicates that said external machine is off.

3. The system of claim 1 wherein said radiation emissive semiconductor means is a light emitting diode.

4. The system of claim 3 wherein said electrical signal is an A.C. signal, said system further including rectifying means for half wave rectifying said A.C. signal.

5. The system of claim 4 wherein the first and second resistive means and the capacitive means are selected to cause the time to charge the capacitive means through the first resistive means to be balanced by the time to discharge the capacitive means through the second resistive means, causing the light emitting diode to continue emitting during the non-conducting half cycle of the rectified AC signal.

6. The system of claim 5 further including visual indicator means for indicating to an operator the status of said external machine.

7. An emission sensitive circuit for interfacing a digital computer with an external machine, the computer having a radiation emissive semiconductor means coupled thereto to receive from the computer a logic signal indicative of a desired status of the external machine, and responsive to emit radiation according to a predetermined logic conditIon of the logic signal comprising:

a. a phototransistor optically coupled to the radiation emissive semiconductor means and operative to be switched on by radiation;

b. a diode bridge rectifier;

c. an SCR connected across first and second terminals of the rectifier, and having a gate terminal connected to the emitter of the phototransistor;

d. a control signal line; and

e. a triac having an input terminal coupled to the control signal line and coupled to a third terminal of the rectifier, a gate terminal coupled to a fourth terminal of the rectifier and an output terminal coupled to the external machine, the control signal thereby providing power to the emission sensitive circuit.

8. The circuit of claim 7 wherein said control signal is an A.C. power signal, said circuit further comprising first and second resistors respectively connecting said first and second terminals of said rectifier to the collector of said photo transistor.

9. The system of claim 8 wherein said radiation emissive semiconductor means is a light emitting diode.

10. The system of claim 9 further including visual indicator means for indicating to an operator the status of said external machine.