Optical traffic preemption detector circuitry
First Claim
1. A detector for receiving pulses of light from an emergency vehicle and sending an output signal to a remote phase selector, the detector comprising:
- photocell means for providing an electrical signal in response to pulses of light received;
rise time filter means coupled to the photocell means for removing constant and slowly varying components from the electrical signal provided by the photocell means and allowing quickly changing pulse components of the electrical signal to pass;
band pass filter means coupled to the rise time filter means for generating a decaying packet of electrical pulses from each pulse provided by said rise time filter means; and
output means coupled to the band pass filter means for providing the output signal based upon the decaying packet pulses, whereby the amplitude of each received pulse of light is represented in said output signal as said packet of electrical pulses in which the number of successive pulses and amplitude of the final pulse in each packet represents the amplitude of the corresponding received pulse of light so that the output signal can have a relatively low maximum level consistent with integrated circuits and still be relatively immune to noise sources present in transmission lines coupling the detector to said remote phase selector.
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Accused Products
Abstract
An optical traffic preemption detector detects pulses of light emitted by an approaching emergency vehicle and provides an output signal which is processed by a phase selector. The phase selector can request a traffic signal controller to preempt a normal traffic signal sequence to give priority to the emergency vehicle. A detector assembly is mounted in proximity to an intersection and can have multiple detector channels. A detector channel can have multiple photocells. Each photocell is provided with a rise time filter. If a detector channel has more than one photocell, the outputs of the respective rise time filters are coupled together. An output of a rise time filter, or coupled rise time filters, is first applied to a current-to-voltage converter and then a band pass filter. The band pass filter isolates a decaying sinusoid signal from a signal representative of a pulse of light. The decaying sinusoid signal is processed to produce a detector channel output signal that has a number of pulses for each pulse of light.
88 Citations
21 Claims
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1. A detector for receiving pulses of light from an emergency vehicle and sending an output signal to a remote phase selector, the detector comprising:
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photocell means for providing an electrical signal in response to pulses of light received; rise time filter means coupled to the photocell means for removing constant and slowly varying components from the electrical signal provided by the photocell means and allowing quickly changing pulse components of the electrical signal to pass; band pass filter means coupled to the rise time filter means for generating a decaying packet of electrical pulses from each pulse provided by said rise time filter means; and output means coupled to the band pass filter means for providing the output signal based upon the decaying packet pulses, whereby the amplitude of each received pulse of light is represented in said output signal as said packet of electrical pulses in which the number of successive pulses and amplitude of the final pulse in each packet represents the amplitude of the corresponding received pulse of light so that the output signal can have a relatively low maximum level consistent with integrated circuits and still be relatively immune to noise sources present in transmission lines coupling the detector to said remote phase selector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A detector channel for receiving pulses of light from an emergency vehicle and sending a signal to a remote phase selector, the detector comprising:
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first photocell means for providing an electrical signal that varies with an intensity of light striking the first photocell means; first rise time means coupled to the first photocell means for removing constant and slowly varying components from the electrical signal provided by the first photocell means and allowing quickly changing pulse components of the electrical signal to pass; summing means coupled to the first rise time filter means for combining an output from additional rise time filter means with an output from the first rise time filter means; band pass filter means coupled to the summing means for generating a decaying packet of pulses from each pulse provided by the summing means; and output means coupled to the band pass filter means for producing the output signal based upon the decaying packet pulses, whereby the amplitude of each received pulse of light is represented in said output signal as said packet of pulses in which the number of successive pulses and amplitude of the final pulse in each packet represents the amplitude of the corresponding received pulse of light so that the output signal can have a relatively low maximum level consistent with integrated circuits and still be relatively immune to noise sources present in transmission lines coupling the detector to said remote phase selector. - View Dependent Claims (19, 20, 21)
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Specification