Ben Smithurst :: CurrentCost (Electricity usage monitor)

CurrentCost (Electricity usage monitor)

The CurrentCost is a device to monitor electricity usage, with the particularly interesting aspect being that it has a serial port to connect it to a PC to log/analyze the data.

I bought a USB cable from CurrentCost's ebay store which arrived quickly and works well with FreeBSD - I assume it would work with Linux too, it didn't when I quickly tried it but I think I didn't have the right kernel module loaded. On FreeBSD you need the ucom and uplcom modules, and the cable works on my old FreeBSD 5.5 machine. I think the pl2303 module is needed on Linux but I didn't get as far as trying it.

Update: Since writing this I have moved my currentcost monitoring to a Linux box and it does indeed work correctly with the pl2303 module loaded.

Then comes the interesting bits, how to read the data, and what to do with it.

Firstly I started submitting the data to an existing system for tracking household spending/utility usage etc, The Tracker.

I created an SQLite database to store the data:

#!/bin/sh

# Create the SQLite DB

if [ -f sqlite.db ]; then
	echo "Error: sqlite.db already exists"
	exit 1
fi

sqlite3 sqlite.db <<EOF
CREATE TABLE readings (
	id INTEGER PRIMARY KEY AUTOINCREMENT,
	ts datetime,
	device_time time,
	watts int(11),
	temp double,
	device_offset int(11),
	ts_delta double(8,2),
	joules int(11)
);

create index ts_index on readings(ts);
EOF

Initially I used MySQL but since my MySQL server is a separate machine from the one with the CurrentCost connected, I figured it made more sense to keep it all on one machine, and SQLite saves the overhead of running MySQL.

Additionally, to create pretty graphs, I store the data into an RRD file as described at http://www.jibble.org/currentcost/.

Then I run a perl script to read the data from the serial port and update both databases. The code is based on the perl code at http://www.jibble.org/currentcost/ too.

To make sense of the data, I use a simple PHP page, deliberately keeping the output very simple so it works on my pocket PC.

For the curious, here's a preview of the web output. The database looks something like this:

+-----+---------------------+-------------+-------+------+---------------+----------+--------+
| id  | ts                  | device_time | watts | temp | device_offset | ts_delta | joules |
+-----+---------------------+-------------+-------+------+---------------+----------+--------+
| 391 | 2008-10-14 19:49:41 | 19:42:41    |  2288 |   15 |          -420 |     6.05 |  13833 | 
| 390 | 2008-10-14 19:49:35 | 19:42:35    |  2290 |   15 |          -420 |     5.98 |  13701 | 
| 389 | 2008-10-14 19:49:29 | 19:42:29    |  2359 |   15 |          -420 |     5.95 |  14031 | 
| 388 | 2008-10-14 19:49:23 | 19:42:23    |  2218 |   15 |          -420 |     6.01 |  13339 | 
| 387 | 2008-10-14 19:49:17 | 19:42:17    |  2280 |   15 |          -420 |    25.03 |  57062 | 
| 386 | 2008-10-14 19:48:52 | 19:41:53    |  2228 |   15 |          -419 |     4.95 |  11024 | 
| 385 | 2008-10-14 19:48:47 | 19:41:47    |  2193 |   15 |          -420 |    11.96 |  26228 | 
| 384 | 2008-10-14 19:48:35 | 19:41:35    |  2209 |   15 |          -420 |    23.93 |  52868 | 
| 383 | 2008-10-14 19:48:11 | 19:41:11    |  2288 |   15 |          -420 |    18.98 |  43422 | 
| 382 | 2008-10-14 19:47:52 | 19:40:53    |  2216 |   15 |          -419 |    10.93 |  24227 | 
| 381 | 2008-10-14 19:47:41 | 19:40:41    |  2340 |   15 |          -420 |     5.77 |  13507 | 
| 380 | 2008-10-14 19:47:35 | 19:40:36    |  2303 |   15 |          -419 |    30.85 |  71048 | 
| 379 | 2008-10-14 19:47:05 | 19:40:06    |   835 |   15 |          -419 |    16.87 |  14083 | 
| 378 | 2008-10-14 19:46:48 | 19:39:48    |   833 |   15 |          -420 |     6.04 |   5031 | 
| 377 | 2008-10-14 19:46:42 | 19:39:42    |   832 |   15 |          -420 |    11.92 |   9920 | 
| 376 | 2008-10-14 19:46:30 | 19:39:30    |   849 |   15 |          -420 |    18.09 |  15357 | 
| 375 | 2008-10-14 19:46:12 | 19:39:12    |   833 |   15 |          -420 |    18.97 |  15800 | 
| 374 | 2008-10-14 19:45:53 | 19:38:54    |   849 |   15 |          -419 |    17.08 |  14505 | 
| 373 | 2008-10-14 19:45:36 | 19:38:36    |   834 |   15 |          -420 |     5.98 |   4984 | 
| 372 | 2008-10-14 19:45:30 | 19:38:30    |   831 |   15 |          -420 |     5.95 |   4941 | 
| 371 | 2008-10-14 19:45:24 | 19:38:24    |   825 |   15 |          -420 |     5.95 |   4907 | 
| 370 | 2008-10-14 19:45:18 | 19:38:18    |   836 |   15 |          -420 |     6.01 |   5024 | 
| 369 | 2008-10-14 19:45:12 | 19:38:12    |   828 |   15 |          -420 |     7.07 |   5856 | 
| 368 | 2008-10-14 19:45:05 | 19:38:06    |   823 |   15 |          -419 |    28.92 |  23798 | 
| 367 | 2008-10-14 19:44:36 | 19:37:36    |   822 |   15 |          -420 |    17.90 |  14714 | 
| 366 | 2008-10-14 19:44:18 | 19:37:18    |   826 |   15 |          -420 |     5.98 |   4938 | 
| 365 | 2008-10-14 19:44:12 | 19:37:12    |   826 | 14.9 |          -420 |    12.92 |  10671 | 
| 364 | 2008-10-14 19:43:59 | 19:37:00    |   817 |   15 |          -419 |    10.95 |   8949 | 
| 363 | 2008-10-14 19:43:48 | 19:36:48    |   828 |   15 |          -420 |    24.08 |  19937 | 
| 362 | 2008-10-14 19:43:24 | 19:36:24    |  2359 | 14.9 |          -420 |     6.01 |  14185 | 
+-----+---------------------+-------------+-------+------+---------------+----------+--------+

This data highlights the only minor problem with the device - it quite often doesn't receive the broadcasts from the meter unit, which should be every 6 seconds, however I think the data should be accurate enough. Also the clock on my device is 7 minutes slow, but that is not a major concern.

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