Hardware manual

US 7,915,570 B2
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across a de?ned range, which may act as a set point for the
current regulator (see element 860 of FIG. 7A) in order to
control the output current (i.e., the current pulse) on the load
(i.e., the one or more light sources). This voltage may be
mapped to output currents between 0 and full scale. In other
embodiments, other ranges of output currents and PWM volt
ages are contemplated. Thus the setpoint generator 720 may
be operable to generate the PWM signal to set the one or more
control values of the control loop to a desired level.
The current regulator 860 (see FIG. 7A) may use a control
loop that may include a sense resistor 836 with a high side
sense with an embedded error ampli?er 808 and a PWM
modulator 810. As mentioned above, when the lighting con
troller starts from a discharged state, it may need time to
achieve the desired level of output due to a delay attributed to
soft start circuits, output capacitance and/or loop response
time, among others. By using the feedback loop, a control
voltage may be kept stored in a capacitor even when the light
source is disconnected. The next time the control loop may be
activated, the PWM modulator 810 may start on the last duty
cycle and thus bypass any settling time. However, as men
tioned above, one or more factors such as capacitor discharge,
leakage currents on surrounding elements, any PCB losses,
contamination etc., may all contribute to decay in this voltage,
and thus over time the memory of the correct duty cycle may
be lost.
One way to solve this issue is to actively holdthe voltage on
a capacitor to compensate for these losses. This can be
achieved by a sample and hold circuit 856, which in some
embodiments may be created using a microcontroller 832
with an integrated ADC (analog-to-digital converter) and
PWM DAC (digital-to-analog converter). In some embodi
ments, one or more control values of the circuit during the
active operation, such as a voltage in the control loop (e.g.,
across a capacitor in the control loop), may be sampled and
stored in memory. A copy of the one or more control values
may be created using the microcontroller’s 832 PWM DAC.
For example, the measured and then re-generated voltage
may be looped (such as to the capacitor) via a large resistor.
The control loop may use an RC circuit 730 to facilitate the
sample and hold of the control values. In some embodiments,
the RC circuit may include capacitors 828A-B, several resis
tors 826 and 830A/B, and other elements.
The regulator 860 may disconnect the capacitor during the
off time of the strobe. This may create high impedance and
thus provide a path to the voltage copy on the PWM DAC
from the microcontroller 832. Since this is driven by active
circuitry (i.e., the microcontroller 832 and the control loop),
the voltage on the capacitor may be maintained for as long as
needed, without risk of discharge due to any effects such as
leakage, temperature, contamination on the board, among
others.
In some embodiments, because the timing of the current
pulse should be synchronized to the exposure time of the
image sensor to ensure consistent illumination of the object
being imaged, an additional input synchronized to the expo
sure may be sent to the lighting current controller to indicate
when to strobe. In other embodiments the synchronization
may be achieved in other ways, such as by implementing
delay elements on the exposure strobe, or by other means.
Since the output capacitors can also be discharged, the FPGA
802 may also send maintenance strobes to the lighting current
controller as needed, such as when the delay interval is suf
?ciently long that the voltage change on the output capacitor
is signi?cant. By brie?y enabling the switching controller, the
maintenance strobe may restore the voltage on any output
capacitors. During these maintenance strobes, the load (one
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or more light sources) may be disconnected to prevent the
maintenance strobes from being noticeable to the user.
Thus, a smart camera 110 may utilize a lighting current
controller 290 in order to provide a current pulse to one or
more light sources. In other words, the smart camera may be
able to provide control and power to one or more standard/
off-the-shelf light sources without using external lighting
current controllers and/or additional power supplies.
Thus embodiments of the invention use many of the aspects
of an external lighting current controller with the ease of use
of integrated lighting, yet without sacri?cing quality.
Embodiments of the invention may also allow the user to
connect and power almost any off-the-shelf light source
directly to the smart camera.
Although the embodiments above have been described in
considerable detail, numerous variations and modi?cations
will become apparent to those skilled in the art once the above
disclosure is fully appreciated. It is intended that the follow
ing claims be interpreted to embrace all such variations and
modi?cations.
What we claim:
1. A smart camera with an integrated universal current
controller, the smart camera comprising:
a processing unit;
an imager coupled to the processing unit; and
an integrated universal current controller con?gured to
couple to one or more external light sources, wherein the
integrated universal current controller is further con?g
ured to generate a current signal to control operation of
the one or more external light sources, wherein the inte
grated universal current controller comprises:
a switching power supply con?gured to generate the
current signal to provide power to the one or more
external light sources; and
an active circuit con?gured to implement a control loop
to regulate generation of the current signal,
wherein the active circuit is con?gured to sample one
or more control values of the control loop while the
control loop is substantially in an active state, and
wherein, in response to a control signal or a user
initiated request, the active circuit is con?gured to
restore the one or more control values of the control
loop while the control loop is substantially in an
inactive state.
2. The smart camera of claim 1, wherein the integrated
universal current controller is con?gurable by the processing
unit to generate the current signal with desired timing and at
a desired level.
3. The smart camera of claim 1, wherein the processing unit
is further con?gured to control exposure of the imager and to
tune timing of the current signal relative to the exposure of the
imager.
4. The smart camera of claim 1, further comprising:
a ?rst port con?gured to couple to an external lighting
controller, wherein the smart camera is con?gured to
control the external lighting controller, and wherein the
smart camera is con?gured to synchronize timing of the
integrated universal current controller with timing of the
external lighting controller.
5. The smart camera of claim 1,
wherein the integrated universal current controller further
comprises:
a setpoint generator con?gured to generate a setpoint
pulse width modulation (PWM) signal, wherein the
setpoint PWM signal is con?gured to set the one or
more control values of the control loop to a desired
level;