Electrical timer modules that interact with one another so as to effect random operation of a plurality of electrical devices, creating the appearance that the devices are not operated automatically. The timer modules include circuitry that allows them to wake up from a sleep state or mode within a random time interval. Upon waking from the sleep state or mode, each modular timer initially senses for the presence of a transmitted signal. Upon receipt of a transmitted signal each module returns to its sleep state or mode. If no transmitted signal is received, the first timer module that wakes up transmits a signal to the other modules and activates an electrical device connected thereto.

Electrical timer modules that interact with one another so as to effect random operation of a plurality of electrical devices, creating the appearance that the devices are not operated automatically. The timer modules include circuitry that allows them to wake up from a sleep state or mode within a random time interval. Upon waking from the sleep state or mode, each modular timer initially senses for the presence of a transmitted signal. Upon receipt of a transmitted signal each module returns to its sleep state or mode. If no transmitted signal is received, the first timer module that wakes up transmits a signal to the other modules and activates an electrical device connected thereto.

For generating random numbers, the output of a random pulse generator having a radioactive source is monitored and the number of decay events detected counted over a predetermined time period. The number of detected events is then compared to one or more selected numbers and a first signal, for example binary "1", is produced where the detected count is equal to the one or more selected numbers and a second signal, binary "0", is produced where the detected count does not equal the one or more selected numbers. The time period is determined so that the probability of the first signal being generated is equal to the probability of the second signal being generated. In this way a truly random number can be generated by repetition of the method steps described above producing a stream of binary "1's" and "0's". Virtually no radioactivity is required for the apparatus to operate and it can in principle be integrated into a single chip.

An apparatus and method is disclosed that provides a random data generator that is less susceptible to error sources resulting from negative feedback biasing. This invention utilizes a shift register and a multiplexer, controlled by the shift register, to provide the feedback to an amplifier. This improves the correlation between the present data output bit and the following bit.

A method and apparatus for grey level printing includes a plurality of recording elements which are enabled for variable periods of time during a cycle of recording grey level pixels. For each recording element a comparator compares the count in a time-changing exposure counter with a multibit grey level data signal. The exposure counter is decremented/incremented by exposure clock pulses from a programmable exposure clock. The exposure clock includes a master clock and an address counter that provides an incremented address signal in response to each set of N pulses from the master clock. The address signal identifies a location in memory of a set of signals used to generate exposure clock pulses. The set of signals is output in parallel to a serial shift register and shifted out serially to form the exposure clock pulses for decrementing/incrementing the exposure counter.