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Possible CYBOT Processor 1 Power-Up problem


Following on from a post in the RealRobots Message Board:

Problem: Cybots seeks light without Antennae Leds connected, but not with them conected.

Many people had offered a number of helpful ideas.
My first idea was to suggest the reset mod.

When I thought about it a little more, the overall situation became more obvious:

There seems to be a problem with the power-up sequence.
When switched on by the switch, the following occurs:

1. 6v is applied directly to the 6v rail, which also supplies the LED's for the Antennae.
2. 9v is applied to the 5v regulator, via a 10 ohm resistor.

This is fine, but just after the 10 ohm resistor, is a 220uF capacitor.
This takes a short while to charge, via the 10 ohm resistor.

Technical stuff aside, the 6v is available before the 5v.
The 6v rail feeds the microcontroller a small amount of voltage through the LED's.

Potentially, the micro can be placed in an unknown state because of this.

To prove this, i simply disconnected the PP3 battery and switched my CYBOT on.
I measured the 5v rail with a meter, it was showing 1.3v

This is enough to possibly start things happening in the micro.

If the power was applied through the power pins of the micro,
the internal Power On Voltage Detector system would hold the unit in RESET until the
required input was applied.

This is applied via an IO pin, not the power supply pins... therefore unknown results. maybe..

I think that adding the resistor to reset may cure this.

Also, as the future boards that have the brown-out circuit included, this should not be a real problem.