US3879137A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Control circuit for an exposure meter
Assignee: Pentax Corp
•
Filing: 1973-09-19
•
Granted: 1975-04-22
•
Expires: 1993-09-19
Abstract
Abstract An exposure meter control circuit which controls the duration of the operation of the exposure meter by determining the time during which the meter is energized from an electrical energy source. The control circuit has a grounded-emitter transistor with the exposure meter connected as the output load thereof and coupled across the electrical energy source for passing current from the source to the exposure meter when the transistor is in a conductive state. A timing circuit, including a capacitor and resistor connected in parallel, is electrically connected to the base of the transistor. A switching device serially connected between the timing circuit and the electrical energy source, when placed in a closed position, instantaneously charges the capacitor with a voltage from the energy source, whereby the voltage across the capacitor is applied to the base of the transistor rendering it conductive until the voltage across the capacitor discharges through the resistor.
Inventors
- 👤 Tadazumi Sakazaki
- 👤 Hirokazu Ando
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 18:27
CPC Classifications
G; G01; G01J; G01J1/00; G01J1/42; G01J1/44; G01J1/46; G03; G03B; G03B7/00; G03B7/08; G03B7/081; G03B7/083
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
144 words
A control circuit for controlling the duration of operation of an exposure meter adapted to be energized from an electrical energy source, said control circuit comprising a semiconductor switch including a grounded-emitter transistor means having the exposure meter connected as an output load thereof for passing current from an electrical energy source through the transistor means to the exposure meter, timing circuit meaNs electrically connected to the base of said transistor means for automatically determining the duration of operation thereof and including capacitor means and resistance means connected in parallel, switch means serially connected between said timing circuit means and the electrical energy source for instantaneously charging, when in a closed position, said capacitor means with a voltage which is applied to the base of said transistor mans for rendering it conductive until the voltage across the capacitor means discharges through said resistance means.
Claim 2
Dependent Claim
144 words
A control circuit for controlling the duration of operation of an exposure meter adapted to be energized from an electrical energy source, said control circuit comprising a semiconductor switch including a grounded-emitter transistor means having the exposure meter connected as an output load thereof for passing current from an electrical energy source through the transistor means to the exposure meter, timing circuit meaNs electrically connected to the base of said transistor means for automatically determining the duration of operation thereof and including capacitor means and resistance means connected in parallel, switch means serially connected between said timing circuit means and the electrical energy source for instantaneously charging, when in a closed position, said capacitor means with a voltage which is applied to the base of said transistor mans for rendering it conductive until the voltage across the capacitor means discharges through said resistance means.
Claim 3
Dependent Claim
144 words
A control circuit for controlling the duration of operation of an exposure meter adapted to be energized from an electrical energy source, said control circuit comprising a semiconductor switch including a grounded-emitter transistor means having the exposure meter connected as an output load thereof for passing current from an electrical energy source through the transistor means to the exposure meter, timing circuit meaNs electrically connected to the base of said transistor means for automatically determining the duration of operation thereof and including capacitor means and resistance means connected in parallel, switch means serially connected between said timing circuit means and the electrical energy source for instantaneously charging, when in a closed position, said capacitor means with a voltage which is applied to the base of said transistor mans for rendering it conductive until the voltage across the capacitor means discharges through said resistance means.
Claim 4
Dependent Claim
144 words
A control circuit for controlling the duration of operation of an exposure meter adapted to be energized from an electrical energy source, said control circuit comprising a semiconductor switch including a grounded-emitter transistor means having the exposure meter connected as an output load thereof for passing current from an electrical energy source through the transistor means to the exposure meter, timing circuit meaNs electrically connected to the base of said transistor means for automatically determining the duration of operation thereof and including capacitor means and resistance means connected in parallel, switch means serially connected between said timing circuit means and the electrical energy source for instantaneously charging, when in a closed position, said capacitor means with a voltage which is applied to the base of said transistor mans for rendering it conductive until the voltage across the capacitor means discharges through said resistance means.
Claim 5
Dependent Claim
24 words
The combination of claim 1 and comprising additional resistance means electrically interconnected between said timing circuit means and the base of said transistor means.
Claim 6
Dependent Claim
33 words
The combination of claim 1 and wherein a buffer circuit means including Darlington-connected transistors having a high input impedance is connected between said timing circuit means and the base of said transistor means.
Claim 7
Dependent Claim
26 words
The combination as in claim 1 and wherein said resistance means includes a photosensitive resistor for producing a resistance which varies inversely with the light intensity.
Claim 8
Dependent Claim
15 words
The combination of claim 4 and wherein said photosensitive resistor is a cadmium sulfide element.
Claim 9
Dependent Claim
68 words
The combination of claim 1 and including a series circuit having an additional switch means and a resistor connected in series therewith and having a resistance value less than the resistance value of said resistance means, said series circuit being in parallel with said capacitor means so that closure of said additional switch means causes said capacitor means to rapidly discharge through said resistor of said series circuit.
Claim 10
Dependent Claim
16 words
The combination of claim 1 and wherein said switch means automatically opens after an initial closure.
Claim 11
Dependent Claim
16 words
The combination of claim 1 and wherein said switch means is of the push button type.
References Cited (Backward Citations)
US3798500A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-04-21 | 1978-10-21 | 1979-04-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-04-21 | 1982-10-21 | 1983-04-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-04-21 | 1986-10-21 | 1987-04-22 | $7700.00 | Window Closed / Lapsed |