Saturday, December 25, 2010

Proto Board Brain Surgery Technique


Propeller Proto Board
mod to enable a low
power mode

You can easily modify your Parallax Propeller Proto Board to reduce its power draw for longer lasting robotics performance using batteries. The goal is to reduce the power of twenty boards so they can run portable, a single board or series of boards set on your robot platform or a Parallax Boe-Bot for example.
The technique works just as well with one board. In the Brain Blob, there are over 20 boards. To eliminate the use of a tether, Parallax Proto Boards will be modified for power consumption reduction, bringing it to within battery operation range.

The goal is to power the Parallax Proto Board with slightly less power by NOT including the 5-volt and 3.3-volt regulators. An external power supply with 3.3 volts would be used. The objective, feed in the 3.3 volts without it feeding back into the on-board regulators, connect 3.3 volts and ground on the board.

To minimize power on the Parallax Proto Board, I have disabled all the circuitry from the 3.3 volt regulator (inclusive) going backwards to the switch and input. This disables the power LED and the draw from both regulators. Power is fed in externally with a regulated lab bench supply. FYI, don't try to remove either of the power regulators from the Proto Board. They appear to be epoxied on. Trying to remove one could break the board. For power feed in, I soldered a standard connector to the boards and added decoupling capacitors. I have it working fine with power reduction.

Parallax Propeller Proto Board PPPB
An update here: With cog 0 running, the board current reduction technique worked as it draws only 4ma. This is what I wanted to achieve. Any guesses as to the current drawn with all eight cogs running? I should add that all these tests are with the 80MHz clock. Clock reduction can reduce power consumption as reported down to around 2mA.

Summary: Just lift up the middle leg of the LM1086CS-3.3 which is pin number 2 as Vout. No need to solder on anything. There's no short circuit possible because the 3.3-volt circuit is now isolated. Plus, the leg can push back down for re-soldering in the future to return the Propeller Proto Board to its original pristine condition. (It won't break off) To see how this works, take a look at the schematic under Regulators.

Test Conclusions: Here are some test conclusions about modifying the Parallax Propeller Proto Board for less current draw. The unmodified board draws 10ma. This includes the powering up of two voltage regulators and one power LED. The modified board draws 4ma. It disables the the power circuit from the 3.3-volt regulator back to the barrel jack power input. The reference is one active cog with a 5MHz crystal. The modification saves 6mA for each board. For 100 boards, unmodified use 1 amp. Modified use 400 milliamps. The savings is .6 amp. The test does not separate out the LED from the regulators as the majority of the current is likely across the LED. This was not a necessary part of the test because a power indicator light would not be used. For 20 modified boards, the power draw is 80mA total. Unmodified is 200mA. Proto Board current draw is critical for battery operated robots and devices.

Note: With the BASIC Stamp SEED Supercomputer, a common source of power was applied to operate at reduced voltage down around a volt.