Remote Snow Sensor PROTOTYPE Specifications Snow sensing range 0-5" Transmitter/receiver range 5-25' (with 6' or less elevation difference) Receiver readout in inches and tenths of inches Resolution worst case 0.2" Resolution typical case 0.1" Accuracy +/-0.2" Day/night operation Power source 110VAC Transmitter power consumption typical 25W Receiver power consumption typical 1W Transmitter frequency 433.92MHz Update rate 4 seconds Ambient temperature range for transmitter operation 0-60F Ambient temperature range for receiver operation 60-80F Alarm threshold increment 0.1" Alarm threshold value stored in non-volatile memory Safety features Transmitter 110VAC input fused. Thermal fuse connected to power supply. Thermal fuse connected to heater. (The heater is used to maintain the transmitter components within their specified operational range.) Receiver Power adapter DC input fused. Introduction and Operation To determine snow depth for the purpose of snow plowing contracts, contractors typically must keep track of snow fall by periodic observation and measurement or rely on a call service. The disadvantage of periodic observation is that it must be continued through nighttime hours, interrupting sleep that may be necessary to safely operate plow equipment. Call services address this problem, but may not experience the same snowfall levels that are observed locally. The remote snow sensor is an alternative means to locally accessing snow depth at the contractor's home using an outdoor sensor (transmitter) and a indoor receiver. The transmitter uses a sensor to determine the amount of snow accumulated on the sensor platform, and relays this information to the indoor receiver for digital display. The indoor receiver operates much like an alarm clock. Push buttons next to the display set the snow level at which the internal alarm beeper will sound. While the alarm snow level is being set, the receiver displays the alarm snow level, but reverts to the sensed snow level reading after approximately 4 seconds. If the alarm snow level is set to 0 or below the current snow depth, the alarm beeper will sound continuously. The alarm beeper can be shutoff with a recessed micro slide switch. The transmitter is set to a calibrated height above the sensor platform. The transmitter housing is canted backward at a slight angle to prevent the top of the housing from shrouding the sensor platform from snowfall. The sensor platform is porous to prevent false readings from rain or snow melt accumulation, and is covered with a screen material compatible with the transmitter sensor. Small amounts of snow accumulation will typically melt away during daytime hours. Snow that accumulates and remains during daytime hours has to be manually removed to reset the sensed snow level to 0 inches. Controls and Indicators Transmitter The transmitter is sealed to prevent water infiltration, and has no user controls. The red LED on the top of the transmitter blinks each time the transmitter sends out a data packet. It is normal for the LED to turn on immediately when power is first applied, and then go into the blinking mode. Note that the LED blink may be too faint to observe in bright sunlight. Receiver The two push buttons next to the display are the "up" and "down" controls for setting the alarm snow level. The upper button is the "up", and the lower button is the "down". Pushing a button, followed by an immediate release, will increment or decrement the alarm snow level on the display by 0.1". If a button is pushed and held, the alarm snow level will continue to increment or decrement at a rate of about 0.1" per second. The buttons will activate with a light touch and require minimal pressure in the down position. The switch on the top of the receiver controls the alarm beeper. With the switch in the right most position (nearest the receiving antenna) the alarm will sound when the sensed snow level is equal or greater than the alarm snow level. This is the correct position for normal operation. With the switch in the left most position, the alarm beeper is completely disabled. The red LED recessed in the top of the receiver blinks at a rate of about once every 4 seconds. Each blink indicates that the receiver is getting sensor data from the transmitter. The receiver display has 3 digits. Only the two right most digits are used in normal operation since the sensor range is limited to 5.0". Because of the non-linear characteristics of the sensor, initial readings may increment by .1" or .2". The sensor is more accurate near the middle of its range, so readings near 3.0" and above will increment by .1". Calibration Transmitters and receivers are calibrated as a matched pair. A data table is calculated specifically for each sensor, and downloaded to non-volatile memory in the receiver. There are no adjustable components in either the transmitter or receiver. Changes can only be made by re-programming the transmitter and/or receiver. Installation Transmitter The transmitter should be placed outdoors on a level surface that receives the average snow fall level. If the area selected for the transmitter is too close to a building or tree, the snow level may be less than average due to an “umbrella effect” or greater than average due to wind drift. Some experimentation may be necessary to find the best location. An example of a good location in many cases may be the back yard patio, at least 10 feet from the back of the house. Receiver The receiver is for indoor use only. The transmitter signal will be strong enough in most cases to located in any first floor room in a typical 3 or 4 bedroom house. The alarm beep is not extremely loud so the receiver should be located in a room where the alarm can be heard. One of the characteristics of the very low power radio frequency (RF) energy sent from the transmitter is that it can be both absorbed and reflected by the human body. If the receiver is located where people would normally walk between the transmitter and receiver, the RF energy may be absorbed and interrupt the receivers reception. This will delay the receiver display update, but will normally not cause data errors. It is also possible for the RF signal to be reflected so that the receiver gets the original signal plus a slightly delayed copy of the signal. In this case the data stream may be corrupted which will also cause a delay in the receiver update as the corrupted data is discarded. Normally this type of error will correct itself after one display cycle. For the most reliable operation, the receiver should be located where foot traffic will not cross between the transmitter and receiver.