One of the tempting features to add to VK5JST’s Aerial Analyzer is an auto-off function. This would shut down the device if the battery got run down or if there were no adjustments made for, say, 10 minutes. This would be fairly simple to do in the software. The problem is with the hardware.
It is easy to turn off the Picaxe. That is just a matter of issuing the ‘END’ statement. That turns off the microcontroller’s use of a few milliwatts and makes very little difference in the analyzer overall battery power draw. That means that an ‘auto-off’ function is nearly useless unless you can install some sort of power control device.
You could isolate the Picaxe to its own power supply and then use some sort of switching it could use to control the oscillator and related circuits. What some have done is to use a second Picaxe as a power control device. I’ve seen one description of this sort of thing as an effort to reduce battery consumption of an Arduino based sensor device. The idea is for the analyzer controller to signal when it no longer needs power. That would be a pin output going high or something. The control processor would see this and then shut down power to the test instrument.
The control processor would spend most of its time in a sleep state pulling very little power (micro-amps, usually). It’d wake up every second or so to check its sensors to see if something need be done.
For the VK5JST Aerial Analyser, the power draw is about 1 watt. If you use NiCd batteries for a 12v supply, you’d have about 10 watt hours of battery available. That’d keep the analyser up for a full day between charges. From that perspective, a whole lotta’ effort trying to reduce battery draw is probably not all that cost effective.
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