App note: Intelligent lighting controller measures ambient light and tracks time

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Implementation on ambient light and time tracking luminaires controller from MAXIM Integrated, Link here

This reference design explains how to design an intelligent lighting controller that senses and measures the ambient light level with an ambient light sensor (ALS). Equipped with a real-time clock (RTC), the controller also knows when to turn lighting on or off at specified times.

A look inside the DS3231 real-time clock

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Pete posted an article taking a closer look at Maxim’s DS3231 real-time clock:

Fortunately, Maxim also offers the DS3231, which is advertised as an “Extremely Accurate I2C-Integrated RTC/TCXO/Crystal”. This chip has the 32kHz crystal integrated into the package itself and uses a built-in temperature sensor to periodically measure the temperature of the crystal and, by switching different internal capacitors in and out of the crystal circuit, can precisely adjust its frequency so it remains constant. It’s specified to keep time within 2ppm from 0°C to +40°C, and 3.5ppm from -40°C to +85°C, which means the clock would only drift 63 and 110 seconds per year, respectively. Very cool.

See the full post at HeyPete.com blog.

Keep an Old Real Time Clock Module Ticking

Sometimes we run into real problems restoring old machines. [RedruM69] recently ran into a system with a dead Real Time Clock (RTC) module. These modules were used on computers and all sorts of other equipment, storing time, date, and 100 or so bytes of battery backed SRAM (before the days of cheap, plentiful flash memory). Often an external coin cell would supply power to the module. In some cases though, cost savings would take over, and the battery would be incorporated into the module. Such is the case with many Dallas Semiconductor models, and the benchmarq bq3287 module [RedruM69] was working with. If we’re reading the date code right, the module was produced in mid 1995 so we’re well past the advertised 10 year battery life.

Apparently Texas Instruments is the current owner of this design, and they even have a datasheet online. (PDF link). It turns out that the bq3287 is a descendant of the bq3285, except that the battery pin is internally disconnected. For most people this would mean a search for a compatible replacement. An industrious hacker might even whip up something compatible from modern components. Not [RedruM69] though. He broke out his Dremel tool and cut into the potted case. Exposing the internal connections above pins 16 and 20 allowed him to solder two wires on. Connecting these wires to an external coin cell brought the module back to life.

[RedruM69] isn’t the first one to perform this hack. Sun computers kept their MAC address in chips like this. When the battery went dead, the computer was off the network. Hackers have been cutting the modules open and adding batteries for years. You could always forgo RTC modules completely and use the power grid as your timebase.


Filed under: classic hacks