© Bueno Systems, Inc. • TSL1401-DB (2009.10.01)
Page 3 of 52
Here, you can see not only the edges of the bagel and the hole in the middle, but also the intensity
variations caused by the seeds and herbs on its surface.
The overall width (field of view) seen by the TSL1401-DB, using the included 7.9mm lens, is
approximately equal to the subject distance. So, for example, if the module is 1 meter away from the
subject, it will see a linear slice of the subject that’s 1 meter wide and 1/128
th
of a meter high.
Focusing the TSL1401-DB’s lens is accomplished by screwing it in or out. When screwed almost all the
way in, distant subjects will be in focus. To focus on closer subjects, the lens needs to be screwed out a
bit. Once proper focus is achieved, it may be necessary to secure the lens from vibration by wrapping
tape around the lens bezel and lens holder barrel. If the lens is screwed in far enough, a small O-ring
snapped into the crevice between the lens bezel and lens holder barrel will serve the same purpose.
Note:
The use of a thread locker (e.g. Loc-Tite) or any cyanoacrylic adhesive (e.g. Super Glue) is
not
recommended near lens elements, as the fumes can destroy any optical coatings that may be
present.
If you are using the TSL1401-DB with a Parallax MoBoStamp-pe, you can use the PC-hosted monitor
program, described later in this document, as an aid to focusing.
Interface and Basic Operation
Refer to the schematic on the last page of this document for the TSL1401-DB’s pinout, and to TAOS’s
TSL1401R-LF datasheet (available from
www.taosinc.com
) for the sensor chip’s particulars. For normal
operation (i.e. without external strobing or syncing), there are only three signals that need to be
considered:
SI
(digital output to the sensor: begins a scan/exposure),
CLK
(digital output to the sensor:
latches
SI
and clocks the pixels out), and
AO
(analog pixel input from the sensor: 0 – Vdd, or tri-stated if
beyond pixel 128). The TSL1401 datasheet describes these signals in detail, so that description won’t be
repeated here, except as it relates to the BASIC Stamp.
If you are using the TSL1401-DB with Parallax’s DB-Expander (p/n 28325), the pin correspondences are
as follows:
TSL1401R Pin
DB-Expander Pin
AO
A
SI
B
CLK
C
The TSL1401R is a
light-integrating
device. It’s a bit like photographic film in that regard: the longer you
expose it, the brighter the resulting image. Also, like film, it can saturate, such that if exposed too long,
everything – even the darkest subjects – will look completely white. The exposure time (also called
“integration time”) is the time interval between
SI
pulses. (Well, actually, the exposure doesn’t
really
begin until 18 clocks
after
SI
; but it’s often convenient to ignore that detail if those clocks occur quickly
enough.) During each exposure, all the pixels need to be clocked out of the device to prepare it for the
next exposure. However, the exposure interval for each pixel begins and ends with the
SI
pulse, not with
the moment it’s clocked out, as with some other sensors. Therefore, all the pixels get exposed
simultaneously, and the acquired image represents the same interval in time for each of them.
There are two ways to acquire images with the TSL1401R: continuous and one-shot. In continuous
imaging, the
SI
pulses occur in a steady stream, with 129 or more pixel clocks in between, during each
exposure interval. To acquire an image, you need to wait for the next
SI
pulse time before clocking out
