US 20070194166 A1
An electronic dispenser for dispensing sheet products includes an infrared proximity sensor operative to detect a presence of a user's hand at a predetermined location near the dispenser and a feed mechanism configured to engage a sheet product roll to cause a quantity of sheet product to be dispensed therethrough. The infrared proximity sensor is configured to have an adjustable sensitivity to vary a detection range of the infrared proximity sensor. The feed mechanism has a motor operative in response to the infrared proximity sensor to engage the feed mechanism.
1. An electronic dispenser for dispensing sheet products, comprising:
an infrared proximity sensor operative to detect a presence of a user's hand at a predetermined location near the dispenser, the infrared proximity sensor being configured to have an adjustable sensitivity to vary a detection range of the infrared proximity sensor; and
a feed mechanism configured to engage a sheet product roll to cause a quantity of sheet product to be dispensed therethrough, the feed mechanism having a motor operative in response to the infrared proximity sensor to engage the feed mechanism.
2. The dispenser of
3. The dispenser of
4. The dispenser of
5. The dispenser of
6. An electronic dispenser for dispensing sheet products, comprising:
a housing adapted to engage a wall in a recessed manner;
an infrared proximity sensor operative to detect a presence of a user's hand at a predetermined location near the dispenser;
a feed mechanism disposed within the housing, configured to engage a sheet product roll to cause a quantity of sheet product to be dispensed therethrough, the feed mechanism having a motor operative in response to the infrared proximity sensor to engage the feed mechanism.
7. The dispenser of
8. The dispenser of
9. The dispenser of
10. The dispenser of
11. The dispenser of
12. The dispenser of
13. The dispenser of
14. An electronic dispenser for dispensing sheet products, comprising:
a housing adapted to engage a wall in a recessed manner;
an infrared proximity sensor operative to detect a presence of a user's hand at a predetermined location near the dispenser, the infrared proximity sensor being configured to have an adjustable sensitivity to vary a detection range of the infrared proximity sensor;
a feed mechanism configured to engage a sheet product roll to cause a quantity of sheet product to be dispensed therethrough, the feed mechanism having a motor operative in response to the infrared proximity sensor to engage the feed mechanism or operative in response to the sheet product being toward from the dispenser; and
a movable paper level arm which engages the sheet product roll and moves in response to a change of diameter of the sheet product roll.
15. The dispenser of
16. The dispenser of
17. The dispenser of
18. The dispenser of
19. The dispenser of
This application claims the benefit of the filing dates of U.S. Provisional Patent Application No. 60/774,390, filed Feb. 18, 2006 and U.S. Provisional Patent Application No. 60/802,612, filed May 22, 2006, which are herein incorporated by reference in their entirety.
The present disclosure generally relates to sheet product dispensers such as paper towel dispensers, and more particularly, to electronic dispensers for touch-less dispensing of sheet products.
Sheet product dispensers, such as paper towel dispensers, are often provided in public washrooms, adjacent to sinks and in other areas where a convenient and disposable drying medium is desired. Sheet product dispensers that allow “hands-free” or “touch-less” dispensing have recently grown in popularity in public washrooms, as a result of an increased awareness by the public to hygiene. For example, hands-free paper towel dispensers permit paper towels to be dispensed as may be needed without a user having to touch a mechanical surface, which may have been contaminated by people who previously used the mechanical towel dispenser without washing their hands or without having washed their hands well.
Touch-less dispensing also permits ease in dispensing for those individuals with arthritis or other afflictions that would make mechanical dispensing difficult. Additionally, touch-less dispensing permits ease in dispensing for those individuals with paint, grease or other substances on their hands. These individuals with substances on their hands would need to touch a mechanical surface, which would then have to be cleaned.
While touch-less dispensers have been successful in dispensing paper towels, a continual need exists for improvements to electronic touch-less dispensers.
Disclosed herein is an improved electronic touch-less sheet product dispenser.
In one embodiment, an electronic dispenser for dispensing sheet products includes an infrared proximity sensor operative to detect a presence of a user's hand at a predetermined location near the dispenser and a feed mechanism configured to engage a sheet product roll to cause a quantity of sheet product to be dispensed therethrough. The infrared proximity sensor is configured to have an adjustable sensitivity to vary a detection range of the infrared proximity sensor. The feed mechanism has a motor operative in response to the infrared proximity sensor to engage the feed mechanism.
In one embodiment, an electronic dispenser for dispensing sheet products includes a housing adapted to engage a wall in a recessed manner, an infrared proximity sensor operative to detect a presence of a user's hand at a predetermined location near the dispenser; and a feed mechanism disposed within the housing, configured to engage a sheet product roll to cause a quantity of sheet product to be dispensed therethrough. The feed mechanism has a motor operative in response to the infrared proximity sensor to engage the feed mechanism.
In one embodiment, an electronic dispenser for dispensing sheet products includes a housing adapted to engage a wall in a recessed manner, an infrared proximity sensor operative to detect a presence of a user's hand at a predetermined location near the dispenser, a feed mechanism configured to engage a sheet product roll to cause a quantity of sheet product to be dispensed therethrough, and a movable paper level arm which engages the sheet product roll and moves in response to a change of diameter of the sheet product roll. The infrared proximity sensor is configured to have an adjustable sensitivity to vary a detection range of the infrared proximity sensor. The feed mechanism has a motor operative in response to the infrared proximity sensor to engage the feed mechanism or operative in response to the sheet product being toward from the dispenser.
The above described and other features are exemplified by the following Figures and detailed description.
Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:
Disclosed herein is an improved electronic touch-less sheet product dispenser. As will be discussed in greater detail below, embodiments of the touch-less electronic dispenser include a number of improvements over existing touch-less electronic dispensers. For example, in one embodiment, the dispenser can be recessed into a wall as a single unit, thereby allowing for minimal space consumption by the dispenser. In other embodiments, improvements have been made to infrared detection circuitry that allows for variable sensitivity in infrared detection. Embodiments illustrated also advantageously use a minimal number of parts for both the mechanical structure and for the electronic unit. It has, therefore, an enhanced reliability and maintainability, both of which contribute to cost effectiveness. Additional improvements and advantages will be understood by those skilled in the art in light of the following descriptions.
The dispenser is an electronic touch-less (hands-free) paper towel dispenser. As will be discussed in greater detail below, hands-free operation is accomplished via two possible modes (“Hang Mode” and “On-Demand Mode”). The electronics described are located on printed circuit board(s) or the like, which are housed within a housing of the dispenser. The dispenser advantageously has a number of configurations switch settings to customize performance. These settings are located within the dispenser and are not available to the general user. They are accessible when the cover (hood) of the dispenser is unlocked and opened.
Reference is made throughout this disclosure to embodiments that employ paper towel products with the understanding that this disclosure can readily be applied to other sheet products. The term “sheet products” is inclusive of natural and/or synthetic cloth or paper sheets. Sheet products can include both woven and non-woven articles. Examples of sheet products include, but are not limited to, wipers and towels.
Referring now to
The term infrared (IR) is being used herein to describe a form of light energy that has a wavelength of about 750 nanometers to about 950 nanometers. The light energy is above the visible spectrum of the human eye and is suitable for use as a communications medium. Like any light energy, IR light can be reflected by objects and controlled with lens. Furthermore, unlike RF (Radio Frequency), IR light is confined to a single room, but is not susceptible to RF dispensers, such as portable phones, wireless networks, remote control toys, and the like.
In one embodiment, with periodic reference to components illustrated in
The feed roller 26 is typically as wide as the paper roll and includes drive roller 34 and intermediate bosses 36 on the drive shaft 38. The working drive rollers 34 are typically an inch or less in width, with intermediate bosses 36 located between them. In one embodiment, the intermediate bosses 36 are slightly less in diameter than the drive rollers 34. This configuration of drive rollers 34 and intermediate bosses 36 tend to prevent the dispensing paper towel from becoming wrinkled as it passes through the drive mechanism assembly and reduces friction, which advantageously reduces power consumption to operate the feed roller 26 compared to designs with feed rollers having a relatively high surface contact with the paper towel.
Also illustrated in
In one embodiment, a hinge may connect the cover 14 to the back plate 12. The hinge may be provided at an upper portion of the cover (i.e., a location opposite the dispensing portion). Alternatively, the hinge may be located either at a right or left side of the dispenser 10. In one embodiment, as illustrated in
Referring now to
Level arm 70 engages a paper roll 28 and pivots about stub shafts 78 as the diameter of the paper roll decreases. In operation, lever arm 70 pivots between a full roll orientation and a low paper orientation. Extension 79 of level arm 70 engages limit switch 74, and as the paper level decreases the limit switch 74 is triggered. The microprocessor detects a change in limit switch 74 condition caused by a lower paper condition and activates an LED or other visual signaling device to indicate the lower paper condition.
Level arm 70 engages the paper roll 28 and advantageously imparts a retarding force tending to control the free rotation of the paper roll 28 during release. In this manner, level arm 70 minimizes paper jamming by preventing the uncontrolled release of paper from the roll.
In one embodiment, the IR emitter 18 uses an IR diode as the active part of the circuit. A current-limiting resistor is placed between an anode of the IR emitter 18 and a supply voltage. The supply voltage can be 3.3 volt (V), regulated to protect the IR diode from over-current failure. A cathode of the IR emitter 18 is connected to a 3-pole slide switch and a series of resistors. Switching to different positions on the slide switch selects different sets of series resistors, which raises or lowers a total series resistance and allows for higher lower currents through the IR emitter diode. This has the effect of higher lower intensity of IR light being emitted, and therefore changes the maximum effective distance of the reflected IR light energy. An IR pulse train can provide error-free motion detection and filter out interference from external dispensers such as fluorescent lamps, portable phones, cameras, and similar dispensers.
The IR detector 20 of the circuit senses the presence of IR light energy at a predetermined frequency. In one embodiment, when the predetermined frequency of IR light energy is detected, the IR detector 20 uses an internal open collector output, driving the base of an NPN transistor to supply an active (high), and signaling the microprocessor that an active IR reflection has been detected. When the predetermined frequency of IR light energy is not present, or too low in intensity, the detector output returns to an inactive state (low).
The IR barrier 52 directs the IR light energy in a forward direction and protects the IR detector 20 from false triggers that may be caused by the close proximity to the IR emitter 18. The IR barrier 52 also allows for lenses 39 to be used as protection for the IR sensor circuits. In one embodiment, the IR barrier 52 extends from a printed circuit board (PCB) surface to a backside surface of the lens cover, and is made of a material that blocks IR light energy. For example, a variety of different black plastic materials (e.g., rubber foam) are suitable as an IR light barrier.
Referring now to
The motor 29 may be driven by at least one battery or driven off a 100V or 220V AC hookup, or driven off a transformer which is run off an AC circuit. The batteries may be non-rechargeable or rechargeable. In one embodiment, the motor and any other electrical components in the dispenser 100 may be powered by four 1.5 volt batteries 33 (6 volts DC). The batteries are housed in a battery compartment 31. Power from the batteries 33 is also supplied to the microprocessor circuit board 56.
Power and signals are distributed from the microprocessor board 56 to the motor 29, the switch printed circuit board 57 and the infrared sensor circuit board 46 via wire harnesses as the circuitry and software dictate. In one embodiment, the microprocessor board 56 comprises a microprocessor and four slide switches 35 to determine sheet length, sheet delay, activation sensor sensitivity and dispense mode (hang or on-demand).
A tear bar mechanical limit switch 58, which is in operable communication with the tear bar 41, may also feed to circuit boards 46, 57. During operation, user action is detected by a tear bar 41. This serrated bar perforates the paper sheet as the user pulls to tear off the paper sheet. Set on a pivot point, the tear bar 41 action also engages (then releases) a switch mechanism, thus informing the electronics of user activity. A time delay between sheet feeds (configurable) is designed to allow a pause between dispensing.
In one embodiment, the circuit boards 56, 57, either alone or in combination, can comprise a manual feed switch, low battery LED, a Hall effect sensor to sense the feed roller 26 position, a magnetic reed switch to indicate if cover is closed/open, respective electrical components and circuitry. Components of circuit boards 56, 57 may be combined on a single board or be positioned on different boards.
Referring to FIGS. 15A-C and 16-17 with periodic reference to elements found in
In one embodiment, the MCU is the Microchip PIC 16F88. Key features of PIC 16F88 include, but are not limited to, nanowatt low power sleep mode, internal ADC (analog to digital conversion), internal oscillator, and 4k ROM program space. To conserve battery life, the MCU spends greater than or equal to 99% of its time in low power sleep mode. It awakes according to its internal programmed timer and determines if paper needs to be ejected. If a sheet does need ejecting, the MCU powers up other circuitry for the tasks, monitors the dispensing, and then goes back into sleep mode.
In one embodiment, the dispenser (10, 100, see
During Hang Mode, on power up, the dispenser 10, 100 initializes itself and assumes the cover 14 is open. Once the cover 14 is determined to be closed, the dispenser 10, 100 waits five seconds and then enters normal operation. The activity light emitting diode (LED) indicator, which is visible via IR window 16, lights for the specified delay duration and a sheet is ejected. The LED remains lit for the duration of the inter-sheet delay to let the user know it is busy and not able to respond. When the hanging sheet is torn off, the configured inter-sheet delay begins. Once this time period has elapsed, the program loop begins again, lighting the LED and ejecting another sheet. As its name suggests, hang mode leaves a sheet hanging from the dispenser.
During On-Demand Mode, on power up, the dispenser 10, 100 initializes itself and assumes the cover 14 is open. Once the cover 14 is determined to be closed, a five second delay is provided. The MCU enters low power sleep mode. Every 100 milliseconds (ms), the MCU wakes up and activates an infrared (IR) beam for a short burst (micro seconds). IR window 16 allows the IR beam out of the dispenser 10, 100. If a hand (or similar object) is placed such that the beam is reflected back to the dispenser 10, 100, detection is made and a sheet is dispensed. If no detection is made, the MCU returns to low power sleep mode for another 100 ms.
After the user tears off the dispensed sheet, the configured inter-sheet delay elapses. After this delay, the 100 ms wake/IR beam sequence begins again. This pause ensures a minimum delay between possible hand detects and sheet feeds. As with Hang Mode, the Activity LED lights during this pause to inform the user that the dispenser 10, 100 is busy. The Activity LED can also light upon detection of a hand, as well as during the dispensing of a sheet.
To conserve power, the IR beam is turned on 10 times a second (i.e., every 100 ms). Thus, a fast hand waved in front of the dispenser may sometimes be missed. Reliable detection is made by a stationary hand that is present in front of the IR window 16 for more than one-tenth of a second. Stated another way, the dispenser 10, 100, in at least one embodiment, is not a motion-activated dispenser, but instead is a physical presence sensing dispenser (e.g., a dispenser that detects the presence of a human hand or other object).
In one embodiment, the IR detector 20 may be tuned to detect 455 kilohertz (kHz) pulse trains and may need 6 pulses to 10 pulses to determine its response. Upon detection, the IR detector 20 asserts its output line to the MCU. To avoid false detections (e.g., random ambient light, reflections, electronic interference, and the like), the MCU samples the IR detectors output 8 times. If all 8 samples are positive (i.e., steady hand detect), then the firmware declares a detection. If fewer then 8 detects are noted, the firmware declares no detect. This voting process happens every time the MCU wakes up and generates the IR beam.
Initialization for both modes is the same. After power up (or any reset), the key configuration registers are updated. This includes timing registers (for watch dog timeout, IR beam frequency generation, and the like), analog to digital conversion module (for battery voltage sampling), port IO pins (direction and start up output states), and clearing the shadow registers for program use. For both modes, the MCU goes into low power mode (sleep) as often as possible to conserve power. Every 100 ms the dispenser wakes itself up, performs the current task at hand, and then goes back to sleep.
In addition to powering down the MCU to save power, the dispenser 10, 100 also powers down other electronics when not in use. This includes a Hall sensor (for motor rotation/sheet length) and the IR transmitter/receiver (for On Demand Mode.) Furthermore, to conserve power, error LEDs can be either off, or blink at 10% duty. In one embodiment, the error LEDs are never continuously on. Status LEDs (such as the Activity LED) are lit continuously during activity. It is noted that when dispensing a sheet, the MCU is on 100% of the time in order to monitor the sheet length. Essentially no power would be saved by sleep mode during sheet dispensing, since the motor drive current is one-thousand times greater than the microcontroller current draw in at least one embodiment.
Multiplexed IO Switch Settings
Due to limited IO pin count on the MCU, some signal inputs are multiplexed together. Three of the MCU's input pins have more than one signal on them:
RB5: L_LENGTH or DOOR_SENSE
RB6: L_DELAY or MODE
RB7: S_DELAY or LOW_PAPER_SENSE
These signals are ORed together with external diodes in hardware. The signals are not active all the time, as this would create electrical conflicts. Instead, two strobe lines controlled by the microcontroller are used to power one line pair or the other. By knowing which strobe line is active, the microcontroller firmware can tell which signal is being reported at the multiplexed input pin. For example:
STROBE—1 asserts DOOR_SENSE, MODE, and LOW_PAPER_SENSE.
STROBE—2 asserts L_LENGTH, L_DELAY, and S_DELAY.
If the microcontroller asserts strobe—1 it knows RB5 will report the status of DOOR_SENSE. If the microcontroller asserts strobe—2, it knows RB5 will report the status of L_LENGTH. Both strobe lines are not powered at the same time.
By diode ORing lines together and driving from a microcontroller port pin, a diode drop is unavoidable. This means the input port pin should have a logic ‘1’ threshold lower than the supply voltage less one diode drop. The PIC 16F88 has two types of input pins, CMOS and Schmitt trigger. Schmitt trigger inputs employ a voltage of 0.8×Vcc=2.64 V for a logic level ‘1’. Thus, any diode drop must be significantly less than 3.3−2.64=0.66 V. Since diode drops are on the order of 0.6-0.7V, Schmitt trigger inputs were avoided for the diode ORed inputs. The CMOS/TTL logic level input pins were used instead as their logic level ‘1’ is 1.6 V.
To provide against noise glitches, debouncing on switch inputs is performed during every read. Switches are sampled every 5 seconds.
This slide switch sets the sheet length dispensed: short, medium, long. It applies to both Hang Mode and On Demand Mode.
This slide switch sets the delay time between sheet feeds: 1 second, 2 seconds, 3 seconds. It applies to both Hang Mode and On Demand Mode.
This slide switch sets detection range for On Demand mode: close, near, far. This setting only applies to On Demand Mode.
This slide switch sets the mode: Hang Mode or On Demand Mode.
The door switch detects if cover 14 of dispenser 10, 100 is open. When the door (e.g., cover 14) is in the closed position, a magnet 60 in the door comes in close proximity to a mechanical reed switch, closing it and thus providing mechanical/electrical contact. The open/closed state of the reed switch is monitored by the MCU. The Door Switch is monitored every five seconds during idle mode. During a sheet dispense, the door in continuously monitored. If the door is opened during motor activity (i.e., a sheet feed), the MCU aborts the feed and disables the motor as a safety precaution.
Low Paper Switch
The low paper switch assembly, including level arm 70, is connected to a mechanical switch that monitors paper level on the roll. When a minimum roll diameter is detected (low paper condition), the switch is closed. In one embodiment, once latched, the only way to clear a low paper condition is to open the door to the dispenser (which resets the MCU.) An out of round condition on paper roll may cause the low paper switch to open and close as the roll rotates. This does not affect low paper detection. The first time the low paper condition is noted, the low paper condition is latched by the MCU.
The IR transmitter is a 400 kHZ to 500 kHz pulse train generated by the microcontroller's hardware PWM module. This signal drives the base of a transistor, which in turn draws current through a pair of IR LEDs hooked in series. Since pulse train generation is handled in hardware, proper waveform timing does not depend on firmware execution time, instruction cycles, loop timing, and the like. In one embodiment, IR LED “on time” is 50% duty (i.e., on half of the time, off half of the time). In one embodiment, to reduce power consumption, the duty (“on time”) has been reduced to about 25%. This is a compromise between reducing the current draw as much as possible, while still ensuring proper pulse width for the IR detection circuitry. In one embodiment, the sensitivity switch allows three different settings for IR transmit power. It selects different combinations of series resistors that limit the current flow through the IR LED(s). Lower current results in lower transmitted power.
In one embodiment, the IR receiver (detector) is tuned to detect a 455 kHz pulse train. It may need 6 pluses to 10 pulses to determine its response. Upon detection, the IR receiver asserts its output line to the MCU. To avoid false detections (random ambient light, reflections, electronic interference, and the like) the MCU samples the IR receiver output 8 times. If all 8 samples are positive (i.e. steady hand detect), then the firmware declares a detection. If fewer then 8 detects are noted, the firmware declares no detect. The microcontroller PWM hardware is incapable of producing a 455 kHz pulse train, hence the next closest setting of 500 kHz. This frequency is still within the IR receiver's detection band, though with a reduced sensitivity.
Shaft Rotation (Determining Sheet Length)
In one embodiment, shaft rotation is monitored by a Hall sensor. A magnet upon the paper roller has 4 poles (N-S-N-S) on it. Thus, one rotation provides four pulses—hi-lo-hi-lo. The MCU counts every edge transition, giving four counts per shaft rotation. This is an improvement over earlier dispenser designs, which counted only the rising edges of the Hall output (i.e., 2 counts per revolution). This change advantageously cuts paper length error in half. The Hall sensor output is open drain, which means an external pull-up resistor is employed for proper operation. This means when powered off, the Hall output signal is pulled up to logic ‘1’. This point makes it unsuitable for diode ORing with other active high signals as it would always report a logic ‘1’, overriding the other signal multiplexed on the input pin. Thus, the Hall sensor output remains on its own dedicated input line.
In one embodiment, with 4 D cells installed, the maximum possible voltage is 4×1.5V=6.0 Volts. The MCU can only sample a maximum input of 3.3 Volts (it's own supply voltage). A resistor divider network is used to cut the battery voltage in half at the microcontroller input pin. Thus, a full reading on fresh batteries reports 6 Volts/2=3 Volts at the microcontroller input pin.
The microcontroller has 10 bits of sampling resolution. To keep the coding simple the two bottom bits (4 counts) are ignored. This yields a resolution of (3.3 V range/1024 sample space)*4 counts=13 mVolts at the port pin, or 26 mV of the true battery voltage. This is actually lower than the tolerances of the circuit components in the voltage divider so no information has been lost by this approximation.
Low battery detection is set for 4 Volts (2 Volts at the MCU port pin after the voltage divider.) It is updated every five seconds. It is not checked during a sheet dispense as such action draws a large amount of current which can cause voltage sags.
Tear Bar and Paper Jams
In one embodiment, the tear bar is a serrated length of metal hinged along the paper chute. As the user lifts a sheet of paper, the teeth cut the hanging paper length from the roll. This action also levers the tear bar on a pivot, asserting the tear bar switch mechanism.
Occasionally, the paper's edge wedges the tear bar in the open position. This prevents it from returning to the non-asserted position. As the firmware uses the tear bar for triggering, it is important that the tear bar return to the non-asserted position. If the tear bar is found stuck open, the motor is advanced approximately one-fourth turn in an effort to free the paper edge. If the tear bar is still asserted, the firmware advances the motor a second time. If this still does not clear the tear bar, a paper jam is declared. The dispenser is held in a non-operative mode and the error/service LED is asserted.
Manual Paper Feed Push Button
The manual feed button allows loading/dispensing of paper to the dispenser. There are no lockouts on motor control via firmware as this push button is tied directly to the motor drive circuitry.
In one embodiment, there are three LEDs located in the IR window 16 in the cover of the dispenser 14: Activity LED, Low Battery LED, and Low Paper/Error LED. The Activity LED lights whenever the dispenser is active. This includes detection of a hand (On Demand mode only), dispensing a sheet, and the inter sheet delay period. All other times, this LED is dark. The Low Battery LED blinks when the battery voltage is determined below desired level. The Low Paper/Error LED blinks when the dispenser requires servicing. This includes a low paper condition, or a paper jam condition. Once set, this LED continues to blink unit the dispenser door is opened and the dispenser is serviced.
System Service Cycle
To conserve battery life, battery voltage, low paper check, and switch settings are checked once every 5 seconds. Therefore, it takes that long to update corresponding LED indicators and switch settings. This means anyone servicing the dispenser will see a 5 second delay before configuration settings are changed. For example: if someone servicing the dispenser switches the mode switch from On Demand to Hang mode, the dispenser will take up to 5 seconds to notice the new switch setting and reset itself for the new mode.
Changing Batteries/Power On
In one embodiment, there is no on/off switch in the dispenser design. As such, the dispenser powers up as soon as batteries are inserted. Electrically speaking, this is a harsh, noisy event from the point of view of the MCU. In general, if a microcontroller does not have a clean power-on transition, the dispenser may power up in a bad state (e.g., lockup). To remedy this possibility, the dispenser design employs a hardware watchdog timer. This monitoring dispenser operates independently of the dispenser firmware code. If the dispenser experiences a harsh start-up and becomes “lost”, the watchdog will eventually time out (approx 32 ms) and perform a system reset. Presumably, the power will have stabilized at this point and a normal power on reset will commence. If not, the watchdog will trigger again and the process will repeat until the power supply is stable and a clean power up has been executed.
After initial power-up is complete, the watchdog is reconfigured to its maximum timeout period (approximately two seconds). In this configuration, the firmware has 2 seconds to clear the watchdog timer, otherwise a system reset will occur. Since normal program loop time is 100 ms there is ample time for normally operating code to keep the watchdog at bay. This provides protection against run time errors.
It is good coding practice to keep the number of watchdog timer reset locations to a minimum. Ideally one location is best. However, due to limitations (listed below), the dispenser firmware has three watchdog reset locations:
In one embodiment, there is a structure to attenuate out of band signals, but in band signals can be generated and accepted from other sources than the dispenser. The presence or absence of the carrier frequency during the ON time of the sampling period is observed. There is no phase relationship requirement at the carrier frequency, nor is there any specific encoding modulation specific to the dispenser.
The overall pulse train is switched on and off approx 10 times per second, at a low duty cycle. The on board MCU accepts a signal during the on time, so this lowers the chances of intercepting a signal from another dispenser. The IR receiver IC from Vishay, uses a narrow band filter to accept only IR signals modulated at a certain rate. In an embodiment, a 455 kHz receiver is utilized. This will accept signals from any other IR source at close to the 455 kHz, as well as from the source generated by the dispenser.
In one embodiment, there is no timing circuit in the dispenser that controls the operation of the motor to control the length of the paper dispensed by the dispenser. The length of the paper is determined by counting pulses from a magnetic encoder wheel on a paper roller, not by timing the length of time that the dispense motor runs. Time between pulses is monitored. If pulse intervals are too great, an error LED flashes to indicate a paper jam. This timing circuit is not a “monostable circuit.” A monostable circuit is typically a set-reset flip flop whose ON time is determined by a single charge of a capacitor through a resistor. Timing in the dispenser is determined by counting multiple clock cycles from a repetitively charging RC clock circuit, often referred to as an “astable circuit”.
In one embodiment, power is supplied to the IR LED in the dispenser from either a battery pack or external AC-DC adaptor. The motor is driven from this raw DC input voltage. The DC input supplies a three terminal voltage regulator that powers the MCU. The MCU switches power on and off to the other circuit elements, the Hall rotation Sensor, Visible LED's, IR LED, and IR receiver.
In one embodiment, there is a structure in the dispenser that protects the rest of the dispenser components from noise/fluctuations generated in the IR LED part. For example, the IR LED circuit may contain a 0.47 micro Faraday (μf) capacitor to supply peak current demand when the LED switches ON.
While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.