Home Statistiscs

Index

1. Index
2. MCP23017 I2C Digital I/O
3. Home Statistics
• Cistern feeding time
• Warm water heat pump time
• Solar pump time
• Cistern level
4. SW
• Class ComI2C

MCP23017 I2C Digital I/O

Here is the full Datasheet of the MCP23017 family.

Home Statistics

Cistern feeding time

This time is measured on the valve which opens, when cistern level is very low. The valve itself have a high magnetic field on the opposite side of the pipe ports. A small magnetic switch or read contact is installed. One side of the switch is connected to ground and the other one to the GPA0 port of the MCP23017. The internal pull up resistor must be switched on. The state of the switch at start up of the programm is stored with date and time. The state of the switch is read out every second and if it had changed, the new state is stored with date and time.

Valve	Switch

Warm water heat pump time

This time is measured ...
The detection and storage is done equal as described above.

Solar pump time

This time is measured ...
The detection and storage is done equal as described above.

Cistern level

The cistern level shall be measured in 4 % steps by using 5 bit in grey code with the following table:

	0 %	4 %	8 %	12 %	16 %	20 %	24 %	28 %	32 %	36 %	40 %	44 %	48 %	52 %	56 %	60 %	64 %	68 %	72 %	76 %	80 %	84 %	88 %	92 %	96 %	100 %
Bit 0	0	1	1	0	0	1	1	0	0	1	1	1	0	0	1	1	0	0	1	1	0	0	1	1	0	0
Bit 1	0	0	1	1	1	1	1	1	0	0	0	1	1	1	1	0	0	0	0	1	1	1	1	1	1	0
Bit 2	0	0	0	0	1	1	1	1	1	1	0	0	0	1	1	1	1	0	0	0	0	0	0	1	1	1
Bit 3	0	0	0	0	0	0	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	0	0	0	0	0
Bit 4	0	0	0	0	0	0	0	0	0	0	0	0	0	1	1	1	1	1	1	1	1	1	1	1	1	1
Hex	00	01	03	02	06	07	0F	0E	0C	0D	09	0B	0A	1E	1F	1D	1C	18	19	1B	1A	12	13	17	16	14

For measuring the water level a closed pipe or rod is used which is mounted in the cistern by hanging on a spring. The pipe or rod must have a density higher than water. The following picture and formulas show the dependency between water level x and change of the spring length.

FFeder: Force on the spring [N] l: lengthen because of force of the spring [m] k1: Spring constant [N/m] d: diameter of pipe or rode [m] m: mass of the pipe or rode [kg] g: acceleration of gravity, 9.81 [m/s2] x: hight of water [m] s: gab between bottom of cistern and actual pipe position, 0 if x = 0 [m] ρ: density of water [kg/m3] lmax: maximum lenghten of spring, s shall be almost 0 [m]

The measurement is done by adding a metal stripe with at least a length of s_max below the spring. s_max is calculated with the above shown formula and the maximum level in the cistern. This plate is connected to ground and isolated on one surface on the places where the table above has zeros. 5 contacts which can slide over this surface are connected to the MCP23017 port A bit 0..4.

Here are the values of my cistern and sensor:
k₁ = N/m
d = m
m = kg
x_max = m

SW

The SW for reading the values is running in the background program "TS_HomeServer" on my Raspberry Pi 2. This program is running as daemon and provides a task system with different cycle times and a init part. This daemon is described here.
All own written SW is stored in the files OwnI2C.cc and OwnI2C.h and is divided in different classes.

Class ComI2C

This class summarises all function needed for the I2C communication using the "wiringPI" library.