US4089012A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Digital exposure time indicating circuit for camera
Assignee: Pentax Corp
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Filing: 1976-11-04
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Granted: 1978-05-09
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Expires: 1996-11-04
Abstract
Abstract A digital exposure time indicating system for a camera includes a light meter whose analog output is proportional to exposure time as a function of preset film sensitivity and aperture opening values, and the measured brightness level. The meter output is fed to a comparator, together with an analog signal from a D/A converter coupled to a counter which accumulates the pulses generated by an oscillator. When the converter output reaches the meter output the comparator signal, acting through a logic circuit, causes the counter signals to be set into a latch, whose outputs are fed through a B/D converter to an LED display.
Inventors
- 👤 Masahiro Kawasaki
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 12:38
CPC Classifications
G; G03; G03B; G03B7/00; G03B7/08; G03B7/091; G03B7/093; G01; G01J; G01J1/00; G01J1/42; G01J1/4209; G01J1/4214; G03B17/00; G03B17/18; G03B17/20
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
184 words
A digital indicating circuit for a camera, comprising: (a) an oscillator; (b) a digital counter for counting the number of pulses generated by said oscillator; (c) a latch circuit for storing, on command, the digital value obtained from said counter; (d) an array of visual indicating elements; (e) a decoder circuit for energizing an indicating element in accordance with the digital value stored in said latch circuit; (f) A D/A convertor for converting the digital value obtained from said counter into an analog value; (g) a light detector for producing an analog output signal proportional to an unknown photographic parameter as a function of preset photographic parameters and a detected brightness level; (h) a comparator for comparing the analog outputs of said D/A converter and said light detector; and (i) logic circuit means responsive to the comparator for commanding the latch circuit to store the value obtained from said counter at an interval of approximately a half cycle of a pulse generated in said oscillator after the output of said D/A converter reaches the amplitude level of the output signal from said light detector.
Claim 2
Dependent Claim
184 words
A digital indicating circuit for a camera, comprising: (a) an oscillator; (b) a digital counter for counting the number of pulses generated by said oscillator; (c) a latch circuit for storing, on command, the digital value obtained from said counter; (d) an array of visual indicating elements; (e) a decoder circuit for energizing an indicating element in accordance with the digital value stored in said latch circuit; (f) A D/A convertor for converting the digital value obtained from said counter into an analog value; (g) a light detector for producing an analog output signal proportional to an unknown photographic parameter as a function of preset photographic parameters and a detected brightness level; (h) a comparator for comparing the analog outputs of said D/A converter and said light detector; and (i) logic circuit means responsive to the comparator for commanding the latch circuit to store the value obtained from said counter at an interval of approximately a half cycle of a pulse generated in said oscillator after the output of said D/A converter reaches the amplitude level of the output signal from said light detector.
Claim 3
Dependent Claim
52 words
A digital indicating circuit for a camera as defined in claim 1, wherein a flip-flop circuit is connected to an output terminal of said counter, and the value obtained from said counter may be stored in the latch circuit only when the output of said flip-flop circuit is in a predetermined state.
Claim 4
Dependent Claim
41 words
A digital indicating circuit as defined in claim 2, wherein said flip-flop circuit has a set terminal, and wherein the counter value stored in the latch circuit is maintained intact in response to an input signal applied to said set terminal.
Claim 5
Dependent Claim
54 words
A digital indicating circuit for a camera as defined in claim 1, wherein the logic circuit means includes means for detecting when each bit of said counter is "1," and wherein, in response to such detection and the output of said comparator, the value obtained from said counter is stored in the latch circuit.
Claim 6
Dependent Claim
53 words
A digital indicating circuit for a camera as defined in claim 1, comprising a D-type flip-flop circuit clocked by a pulse train having a phase opposite to that of the pulse train of said oscillator, and wherein the output of said comparator is fed to an input terminal of said D-type flip-flop circuit.
Claim 7
Dependent Claim
59 words
A digital indicating circuit for a camera as defined in claim 1, wherein an output of said counter is fed to the decoder circuit by a transmission gate, and wherein a "low battery" warning signal is fed to a control terminal of said transmission gate, thereby causing the array of indicating elements to flicker when the battery runs low.
References Cited (Backward Citations)
US3995284A
Cited
US3972626A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1981-05-08 | 1981-11-07 | 1982-05-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-05-08 | 1985-11-07 | 1986-05-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-05-08 | 1989-11-07 | 1990-05-09 | $7700.00 | Window Closed / Lapsed |