Monday, July 05, 2021

Calibrated Sabertooth 2x32 Speed Controller, New Voltage Regulator for Senna Switch 15 on Droid #1

Droid #1 got a little bit of needed attention today. First, I finally got around to calibrating the Sabertooth 2x32 speed controller with the new transmitter (as explained in this post).

Next, I wanted to address a potential concern with powering the Senna Switch 15 box from the Futaba 14SG transmitter. As also mentioned in in this post, the voltage regulator in the Senna Switch 15 box accepts input voltages in the range of 6-28 volts, and outputs 3.3 volts to the box's electronics. Because the new Futaba 14SG transmitter nominally runs on 6 volts (the transmitter itself can run down to 3.9 volts before turning off), as the voltage drops over time, it's possible the Switch 15 would no longer function.

The solution was to find a pin-compatible voltage regulator that can handle a lower voltage range. I found one in the Pololu S7V8F3 voltage regulator. This regulator can take an input range of 2.7 volts to 11.8 volts, and output 3.3 volts (supplying anywhere from 500ma to 1 amp), so this fits the bill. (Note that I'm not using the Shutdown pin; it can and will be left disconnected.) This voltage regulator would even work with the Futaba 10CAG radio. Fully charged, I've never seen its battery (9.6v nominal) above 11.2 volts, so it fits in the range supported by the Pololu voltage regulator.

While I could certainly do the transplant myself, I am on vacation this week and was looking for reason to visit Mike Senna, so I went over to his place for this operation.

The black cubic part underneath the red wires needs to be removed, that's the original voltage regulator that takes a minimum of 6 volts.

Mike removed that part, and soldered in the Pololu part.

All's good! Now I shouldn't have to worry about suddenly not being able to play sounds or perform other functions as the battery discharges with use at events.

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