Saturday, 29 September 2012

Customizing the Logging Shield

In hindsight, two mistakes: not using stacking headers; having the meter stick up too far. Both prevent putting the shield in the middle of a stack where it could be really useful.

It is now over a year later and the RTC has lost about 8 minutes, well within the "minute a month" they advertised for the accuracy of quartz watches back when they were a novelty.

 I started out by assembling the data logging shield per instructions and doing a bunch of experimenting with programming for real time acquisition and logging. The only way to see what's going on on the card is to either watch the LEDs or have it report to the serial monitor on the attached computer, which really limits its ability to function without the computer. I also found myself regularly attaching my multimeter to various pins to see what was going on. A little time and money made the shield more self contained.

A Voltage Display

A DIP switch was added to the prototype area, with all the pins on one side tied to the input of a little voltmeter module. The other side pins connected to digital pins 9 (switch 1) and 3 (switch 2), A0 through A5 (switch 3 to 8). The voltmeter module was hot glued to the SD card housing, with a small piece of sheet plastic in-between.

This gives me switch selectable monitoring of each of the analog inputs and two of the PWM capable output pins. Be sure to set only on of the switches to be on at a time.

Interrupt Push Button

A push button was installed at the bottom right to allow momentary connection of pin 2 to +5 volts to generate an interrupt event.

LEDs for Status

The two LEDs that came with the kit were connected to pins 2 (red) and 3 (green) for additional status indication.