It is a boost regulator, generating
3.3V from a 3V battery. However,
I found a few errors in his design/
documentation.
1. The buck regulator is called
TPS72630 in the text and in the
schematic, and does not exist. He
first mentions the TPS62730
correctly, so I assume it is a simple
transposition.
2. The PUMH10 is
misrepresented in the schematic as
having FETs, rather than the NPN
bipolar devices mentioned in the text
and parts list. The ports of the
BLE112A have enough drive to easily
pull the camera inputs low, so the
buffers could be eliminated (though
don't forget to change the firmware).
Unfortunately, the BLE module's ports
are not truly open-drain. Because of
the uC port's ESD diodes, the outputs
should not be pulled beyond 0.4
volts of the supply, preventing a
direct connection to the camera
without buffers.
3. The 3024 coin battery is
specified at 3.0 volts, not 3. 6 as in
the text and schematic. A fresh one
may read 3. 25 with a Hi-Z meter, but
will quickly drop down with a load
applied.
4. The camera detect power-on
circuitry doesn't fit the text
description regarding the resistors
connected to the input of the Schmitt
inverter. I re-arranged and merged
the schematics to get a clearer
understanding of the connectivity. As
drawn, the detect node will ALWAYS
be low — 0.27 volts. As redrawn (and
shown above) as I think was meant —
with the 1M pulldown connected to
shutter rather than detect — the
circuit is functional. Note there is a
1M + 45K load on the camera
battery which causes a continuous
3. 2 µA drain. When disconnected,
there is an 11M load on the coin cell
as well. (Every nanoamp counts.)
5. I would tend to leave the
camera plug in place for long
periods, since the connector is not
very sturdy and I don't want to cycle
it excessively. I would disconnect the
dongle using the 2. 5 mm plug. With
the plug dangling, it may make
contact with something metallic and
fire the trigger — or at least cause
camera battery discharge. I would
use a female connector on the
camera side and a male on a cable
from the controller.
Steve McChrystal
26 September 2013
READER FEEDBACK Continued from page 7
Continued on page 48