Brigadoon - An Occasional Corner on the Internet
Houseboat Hot Water System
Designed by Mark Little
Hot Water System Controller
PROJECT UNDER DEVELOPMENT
There were a number of options available for the Hot Water System Controller- the Raspberry Pi, the AT89C55, the AT90C8535 and the Arduino. The AT90S8535 and the Arduino were short-listed as they both contain an integral Analogue to Digital Converter (ADC) that will be used to measure the output of the current sensor. The Arduino UNO was selected because I have never used the Arduino before and this seemed like a good introductory project.
The resolution of the Arduino ADC is 5V/1023 (or about 5mV). The current sensor has an output of about 2.5V for 0A input.
Based on the calibration test for the 20A current sensor, which outputs a change in output voltage of 100mV per Amp, the Arduino should be able to detect changes in current of about 5mA
A prototype for the control software has been developed using the I/O Test Jig. The software is quite simple in that it uses the 20A current sensor to read the current flowing through the motor and when that current reaches a pre-set level, the pump is deemed to be on and a timer starts for 1.2-seconds.
If the pump is still running 1.2 seconds later, the inverter is started. This delay is included to stop the re-pressurisation of the water line from unnecessarily triggering the inverter, wasting power.
Once the inverter is running, if the pump stops, another timer is started. If the pump does not come back on within 30-seconds, the inverter is reset to 30 seconds. This timer ensures that the inverter does not stop if the user turns the hot water off and on again a few times while washing hands or similar. This should increase the life of the inverter and the Hot Water System and prevent annoying gaps in the hot water as the inverter will not come on for 1.5-seconds after it stops.
The software has been developed using the Linux Arduino IDE. The Arduino file holding the project will be provided when the documentation has been completed and test is complete.