Today I finally got around to a minor task for droid #2, regarding his sound system.
I'm using a Radio Shack audio amplifier that runs on 9 volts. Until now, I've been using a small 9 volt battery that resides inside the amplifier for its power. There are a number of disadvantages to this:
• The battery requires me to separately turn on and off the amplifier when I power up and down the rest of the droid.
• To get to the amplifier power dial, I need to remove the dome.
• I'm prone to forgetting it's on, thus running down the battery.
The solution is to use the amplifier's power adapter connection, that takes 9 volts DC in. Since my droid runs on a 12 volt power supply, I need to use an LM7809 voltage regulator to convert 12 volts to 9 volts.
The left pin is the 12 volt input pin, and gets connected to the 12 volt positive terminal strip. The center pin is ground, and gets connected to the ground bolt. The right pin is the 9 volt output pin, and gets connected to the positive input to the amplifier.
I added some thermal paste to the back of the regulator, before attaching it to the segment of aluminum angle bracket that I'm using as a heat sink.
Time to test it out in the droid!
It works! Now I can run without a battery in the amplifier, and use just a single on/off switch in the droid.