Darkroom timer

Claim 2

A timer for switching power to and from an external unit, comprising: a. actuator means; b. digital means responsive to said actuator means for providing control signals; c. coupling means for providing the timer with a periodic signal having a first characteristic frequency; d. clock means responsive to said coupling means to produce a series of pulses having a second characteristic frequency related to said first characteristic frequency; e. counter means adapted for receiving a desired selectable digital value, said counter means being responsive to said control signals from said digital means to count pulses from said clock means and produce an output when a digital value entered into said counter means has been counted out; f. programming means for entering a desired selectable digital value into said counter means; and g. switch means responsive to said counter means for switching power to and from an external unit as a function of the condition of said counter means.

Claim 3

A timer as in claim 1, wherein said counter means comprises a plurality of counters successively connected in a cascade configuration, each of said counters having first and second enabling inputs and a clocking input, the first of said enabling inputs on each of said counters being connected to an enabling output on said digital means, said enabling output of said digital means producing an enabling signal when said digital means is actuated, the first of said counters having its second enabling input connected to an enabling output of said digital means and each successive digital counter having its second enabling input connected to an enabling output on the preceding digital counter which produces an enabling signal when the number in said preceding counter is zero whereby said successive counter is pulsed when the selectable value stored in said counter has been counted out and when the counter is subsequently cycled through its full capacity.

Claim 4

A timer as in claim 2, further comprising means responsive to said counter means for detecting when all of said counters have counted out the values stored in them by said programming means and for actuating said digital means to cause said counter means to cease counting.

Claim 5

A timer as in claim 3, further comprising audio means responsive to said clock means for producing a periodic audio signal related to said first and second characteristic frequencies.

Claim 6

A timer as in claim 4, wherein said switch means is a relay.

Claim 7

A timer as in claim 4, wherein said digital means causes said counter means to cease counting by stopping said clock means from producing pulses.

Claim 8

A timer as in claim 4, wherein said second characteristic frequency may be varied between at least two values.

Claim 9

A timer as in claim 1, further comprising audio means responsive to said clock means for producing a periodic audio signal related to said first and second characteristic frequencies.

Claim 10

A timer as in claim 1 wherein said digital means is responsive to the application of power to the timer to generate a clearing signal to clear the counter means of any number which may be stored therein.

Claim 11

A timer as in claim 1 wherein said clock means continues to produce pulses at the end of a timing period whereby said pulses provide timing information for an end of interval alarm.

Claim 12

A timer as in claim 1 wherein the digital means is responsive to a switch to cause the counting means to cease counting and the clock to cease producing pulses and to clear the counter of any digital value contained therein whereby the timer returns to its steady state.

Claim 13

A timer as in claim 1 further comprising display means coupled to said counter means for displaying the value stored in said counter means.

Claim 14

A timer as in claim 12 where said display means comprises a light emitting alpha-numeric display.

Claim 15

A timer as in claim 13 wherein the intensity of the light emitted by said alpha-numeric display is controlled by photosensitive means, said photosensitive means being exposed to ambient light conditions to increase the brightness of said alpha-numeric display under bright light conditions and to decrease the brightness of said display under attenuated lighting conditions.

Claim 16

A timer for switching power to and from a unit, comprising: a. actuator means; b. digital means responsive to said actuator means for providing control signals; c. coupling means for providing the timer with a periodic signal having a first characteristic frequency; d. clock means responsive to said coupling means to produce a series of pulses having a characteristic frequency related to said first characteristic frequency; e. counter means adapted for receiving a desired selectable digital value, said counter means being responsive to said control signals from said digital means to count pulses from said clock means and produce an output when a digital value entered into said counter means has been counted; f. programming means for entering a desired selectable digital value into said counter means; g. switch means responsive to said counter means for switching power to and from the unit as a function of the condition of said counter means; h. audio means responsive to said clock means for producing a periodic audio signal related to said first characteristic frequency; and i. display means coupled to said counter means for displaying the value stored in said counter means.

Claim 17

A timer for switching power to and from a unit, comprising: a. actuator means; b. digital means responsive to said actuator means for providing control signals; c. coupling means for providing the timer with a periodic signal having a first characteristic frequency; d. clock means responsive to said coupling means to produce a series of pulses having a characteristic frequency related to said first characteristic frequency; e. counter means adapted for receiving a desired selectable digital value, said counter means being responsive to said control signals from said digital means to count pulses from said clock means and produce an output when a digital value entered into said counter means has been counted; f. programming means for entering a desired selectable digital value into said counter means; g. switch means responsive to said counter means for switching power to and from the unit as a function of the condition of said counter means; h. audio means responsive to said clock means for producing a periodic audio signal related to said first characteristic frequency; and i. display means coupled to said counter means for displaying the value stored in said counter means.