Looking at a picture of the ssc-32, I think there may be a simple setup for voltage brown out protection for the logic chip with out using a seperate battery. This setup would use a diode (Schottky type prefered for its low .1v voltage drop), and a 1000 uf 16v electrolytic capacitor (or an appropriate substitute) to isolate and maintain voltage to the logic chip during momentary supply voltage drops. The weight of this should be significantly less than a 9v battery. This assumes all - screw terminals are a common ground. Below is what I’d try if I actually had an ssc-32:
Remove the VS-VL jumper.
Connect the diode between the +VS1 (or +VS2) screw terminal and the +VL screw terminal, with the banded end of the diode connected to the +VL screw terminal.
Connect the + lead of the capacitor to the +VL screw terminal and the - lead of the capacitor to the -VL screw terminal.
This is a good idea, and would certainly work to carry the logic through voltage dips. The question is how big a capacitor is needed, which is dependent on the battery voltage and duration of the voltage dip. I just did some quick calculations and came up with the following. Assume the SSC-32 electronics draws 50mA (I don’t remember the exact value, but this is in the right ballpark and makes the numbers come out nicely). Then a 1000uF capacitor will drop 1V every 20ms. With a 6V battery, this arrangement could carry the logic through a dip lasting about 20ms. Increase the battery voltage and/or capacitance to increase the protection. 7.2V and 2000uF would carry it through 100ms or so.
Here’s an alternate suggestion for how to implement this. Make a special VS=VL jumper that contains the diode, crimped or soldered to mating connectors. Place this jumper on the VS=VL pins, put the capacitor in the VL terminal block, and connect VS1 as usual.
If someone has applications that fail due to occasional voltage dips, it would be pretty easy to try different capacitors to see what helps. I agree that it should be a Schottky diode. Performance would be much worse with a 1N4001 or similar.
I did some looking and Jameco has a 5.5v 1 farad memory backup capacitor for $4.49, and BGMicro has 5.5v .22 farad capacitors for $.69 each. These could be used on the logic side of the board as a backup. A diode wouldn’t be needed as long as the voltage regulator doesn’t allow reverse current flow. One could put a multimeter across the VS-VL pins and see how many ma are being used by the board.
I think putting even a single $4 part on a board that retails for all of $40 will pretty much axe the idea. Making provisions on the PCB to make it easily added later by the customer however…
Unfortunately, moving to a lower voltage for the uC is not possible in the current design because of the clock frequency used (14.7456 MHz). Lower voltage operation is only supported at frequencies below 8 MHz. I am also not certain how servos would respond to 3.3V signals, but I suspect most servos would work.
If a Farad capacitor is used on the 5V rail, it could be connected to the 5V pins on the ABCD header (assuming they are not being used for another purpose). I don’t remember if the regulator blocks reverse current flow. A diode might still be needed. But this solution should keep the uC supply above the reset level for several seconds during a supply dip.
A capacitor/diode would incurr some $ investment up front, but 9v batterys are also somewhat expensive, need replacing/recharging, and are probably several times heaver. A capacitor won’t fix all low voltage issues, but is an option. Adding a capacitor to the board would be very simple. Make two shunt jumper connectors like below for the capacitor leads, then slip the open side of the shunt jumpers on a ± pin pair on the ADC pin header. Below is the bgmicro capacitor.
