mweyland / HB9UF ElPiHat - History

Adding diode to address case where DC/DC converter is reverse biased

The datasheet of the DC/DC converter recommends a (normally) reverse
biased diode across the regulator. This is to prevent damage in case
the output is at a higher voltage than the input.

Since this condition would apply if somebody powers the Raspberry Pi
directly (i.e. not using the hat), it is strongly recommended to add
the diode.

Fixes #1

Dropping 3M32 resistor to 1M4.

The DC/DC converter is currently trimmed to 5.1 V. Since the
Raspberry Pi can take more than that, we increase the voltage
to 5.25 V. This appears to be the recommended operating voltage.

In order to achieve this, a trimming resistor of 1M375 is
required. We use 1M4. Since we also use this resistor value to
dissipate stray charge on FET and microcontroller inputs, those
resistors are dropped in value as well. This is a good thing since
the value was uncomfortably high (and still remains somewhat high
even after the change).

Fixes #2.

Fixing typo in README. Thanks to HB9OCQ for spotting this one!

Replacing schematic image with corrected version (polyfuse -> fuse)