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Janice is an eight-channel sprinkler controller designed to be low-cost and flexible. The design includes a protected input for an optional rain sensor, battery-backed scheduling, real-time clock (RTC) and several user-interface options. An optional external display board with five buttons can be included.




Sprinkler Controller

Janice uses the MAC97A6 triac to switch the 24V AC needed to control the system’s solenoid valves. To conserve imp pins for other functions in the design, the gates on the eight triacs are driven by a shift register, which the imp is able to write to via one of its SPI interfaces. An LED on each channel indicates whether that channel is active.

Battery-Backed Scheduling

An optional EEPROM and Battery-Backed Real-Time Clock (RTC) are included in the design. Because the imp's internal RTC is not able to be battery-backed, and is re-synced only on server connect, the optional external data storage and RTC allow the sprinkler controller to resume watering on its last-known schedule if the device experiences a WiFi outage.

The example code includes attempt-to-reconnect when WiFi is lost, while continuing to water on the last known schedule. The device automatically updates its schedule from the cloud as soon as the connection is restored.

Two options are provided for back-up power for the RTC: a secondary lithium coin cell, or a 60μF super-capacitor. Selecting the super-capacitor allows the RTC to run for approximately 100 hours (~4 days, 4 hours) without power, while the coin cell battery allows the RTC to run for approximately 4000 hours (~5.5 months).

Rain Sensor Input

Many states and municipalities require that sprinkler controllers include a rain sensor to prevent watering during wet weather. Conventional sprinkler controllers do not include an input for this sensor; the sensor serves instead as a power cut-off switch to the solenoid valves. The Janice design includes a separate, protected input for this sensor in order to allow more intelligent decision-making with this information.

Because the sprinkler controller is Internet-connected, not simply WiFi-connected, additional information can be used to make intelligent decisions about watering, such as current weather, forecast and regional location.

Human Interface Options

The Janice design can optionally be connected to a display board, which provides a 2x20-character display and five buttons for local control of the system.

An optional beeper is included in the design to provide local feedback to the user.

A single status LED can be used to indicate the connection status or provide other feedback. Each sprinkler channel includes an LED to indicate when that channel is active.

Device Firmware and Example Code

Revision-controlled example firmware for the Janice board is available on the Electric Imp GitHub examples page. The Janice firmware includes several modular classes:

The example agent for Janice serves a simple Web UI that can be used to control the system for testing or demonstration purposes. To use the Web UI, open the agent URL in a browser.

Hardware Design Files

Optional Display Board