Building a temperature probe for the OLPC XO-1

The OLPC XO-1 has a handy Measure application that can measure a signal sent in through the microphone socket. Here I hack Measure to measure temperature and detail the hardware necessary to build the probe.

A SQLite interface in 23 lines of Arc

Paul Graham's Arc language turns out to be pretty succient. In 23 lines of Arc I managed to hack together a working interface to a SQLite database:

(= db! 'nil)

(def db+ (name (o host "localhost") (o port 49153))
 (let (i o) (connect-socket host port)
   (db> o name)
   (if (db< i) (list i o))))

(def sql ((i o) q)
 (db> o q)
 (if (db< i) (readall i 200)))

(def db- (db)
 (map close db))

(def db> (o s)
 (write s o)
 (writec #\return o)
 (writec #\newline o)
 (flush-socket o))

(def db< (i)
 (= db! (read i))
 (iso db! 200))

Calibrating a machine learning spam filter

One problem often encountered with machine learning based spam filters is what to do with the region around 0.5. i.e. how do we intepret a message that's scores as being right in the middle between spam and ham. This post shows how calibrating the filter can help.