ST VD5376 Installation and operating instructions
October 2011 Doc ID 018955 Rev 1 1/16
AN3419
Application note
VD5376/VD5377 optical finger navigation testing
1 Introduction
This document gives a non-exhaustive list of tests which may be run on the ST
VD5376/VD5377 optical finger navigation (OFN) devices.
2 Initialization
The initialization setup depends on the customer application (for example, automatic or
manual power mode, direct 1v8 drive or Vtop supply, CPI setting, X/Y direction and so on).
Please refer to the individual application notes for initialization instructions:
●
AN3356:
Interfacing to the VD5377 optical navigation device
(018567)
●
AN3217:
Interfacing to the VD5376 optical navigation device
(017529)
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Navigation AN3419
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3 Navigation
This chapter describes the navigation tests that can be performed on the VD5376/VD5477
sensors.
3.1 XY table navigation
Using a mechanical setup gives accurate navigation results of how well the module
navigates at various speeds and over various surfaces.
STMicroelectronics suggested (non finger) surfaces for OFN testing are white card, cotton
and leather glove. Care must be taken when choosing surfaces for XY table testing as the
module surface can be easily scratched with surfaces that are too hard. The images in
Figure 1
to
Figure 4
show VD5377 (LOQFP) with standard PC mouse optics on white card.
It demonstrates the accurate navigation achievable with the VD5376/VD5377 sensors.
Figure 1. 2ips Figure 2. 10ips
Figure 3. 20ips Figure 4. 40ips
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AN3419 Navigation
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In an OFN module setup, high accuracy/high speed is not essential. The images (
Figure 5
and
Figure 6
) show what is and what is not (
Figure 7
and
Figure 8
) considered acceptable
OFN navigation (plots below were done at 4ips).
Figure 5. OFN good navigation Figure 6. OFN good navigation
Figure 7. OFN bad navigation Figure 8. OFN bad navigation
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Navigation AN3419
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The navigation in
Figure 5
is oval in shape, but this can be corrected by increasing the X CPI
register setting.
Figure 6
navigation although too small, is circular. The X/Y CPI register settings can both be
increased here to achieve the required CPI value.
Figure 7
shows glitchy navigation while the navigation in
Figure 8
drifts, is too small and
does not complete the full circle. These errors cannot be ‘fixed’ by register settings.
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AN3419 Navigation
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3.2 Finger navigation
Although XY table (mechanical) navigation testing is useful to show the overall accuracy of
the OFN module, the real navigation testing is done by fingers. It is very important to test a
wide range of users/fingers to find the best and worst fingerprints.
The image below shows good finger navigation. The module was tested by manually
swiping a finger across the sensor. One swipe in each direction (
Figure 9
).
Figure 9. Manual finger swipes - good navigation
1
2
3
4
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Navigation AN3419
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Figure 10. Manual finger swipes - bad navigation
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AN3419 Navigation
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Figure 11. Manual Swipes - bad (jittery) navigation
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Typical current consumption AN3419
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4 Typical current consumption
Ta bl e 1
shows typical current consumption on a VD5377.
The figures for the VD5377 Idle and Sleep modes are given at their default settings.
Ta bl e 2
shows typical current consumption on a VD5376.
Automatic power management mode should not be used with VD5376 in applications with
more than one device on the I2C bus.
Table 1. VD5377 typical current consumption
Mode Max exposure
Run fast 10mA
Run medium 6mA
Run Slow 3.5mA
Idle 1 350uA
Idle 2 100uA
Sleep 50uA
Powerdown <1uA
Table 2. VD5376 typical current consumption
Mode Max exposure
Run fast 9mA
Run medium 5mA
Run Slow 3mA
Powerdown 40uA
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AN3419 Images
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5 Images
This chapter describes tests that can be performed on the VD5376/VD5377 sensors that
involve using the sensors to capture images.
5.1 External
It can be useful to take images with an IR camera to show that the navigation surface is
being illuminated effectively.
Figure 12. Example external image
5.2 Internal
There are two methods of getting images from the VD5376/VD5377 sensors. Both are
described in separate application notes.
●Image download over I2C:
–
AN3415:
VD5376 image download over I2C
(018944)
–
AN3414:
VD5377 image download over I2C
(018941)
●Fast image streaming:
–
AN3417:
VD5376 OFN high speed imaging system
(018949)
–
AN3418:
VD5377 OFN high speed imaging system
(018952)
Image download over I2C is very slow on the VD5376 (0.5fps), this is because of the auto
increment I2C read function. This can be disabled on the VD5377, enabling a much faster
image download. Customers can create their own application or use the ST one, along with
the ST OFN test board (PCB1389C) and ST7 firmware. Although this does require the
customer to create their own adapter board for the OFN (see
Figure 13
for size/connector
details).
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Images AN3419
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Figure 13. PCB1389 OFN adapter board
Fast Image Streaming - images are captured in real time. Although four extra test pins are
required on the OFN module for this test mode. See application notes AN3417 and AN3418
for more details.
In both
Figure 14
and
Figure 15
, the image download application shows Features, MEP and
exposure.
Figure 14. VD5377 ST image download application (1x optics)
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Figure 15. VD5376 ST image download application (0.75x optics)
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Images AN3419
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Figure 16
to
Figure 19
show images taken with the VD5377 mouse view application.
A piece of Blu-Tack®(a) is pressed onto the module surface so that it makes good contact
with the whole module top surface. An image is taken of the flattened Blu-Tack. The
Blu-Tack
is used to present an image that is, as diffused as possible, without any ‘features’
.
In
Figure 16
there is nothing on the module. The image should be completely black, but we
can see that there is light leaking onto the sensor from the LED.
In
Figure 17
there is Blu-Tack on top of the module. This should provide a nice flat image (as
in
Figure 18
), but there is some misalignment with the optics and the LED, so we only see
half the image.
a. Blu-Tack®is an adhesive tack product and is a registered trademark of Bostik.
Figure 16. Nothing on top, LED leakage - bad Figure 17. Blu-Tack, RI and centering - bad
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6 Other factors
6.1 Hover
There should be no unwanted movement when a finger or other object is placed a few
millimeters away from the module surface (normal light conditions).
6.2 Jitter
This is defined as unintentional movement due to general noise. The min_features threshold
register must be adjusted or noise reduced to eliminate jitter.
6.3 Sunlight
Another vital test is navigation in bright sunlight. In the absence of direct bright sunlight,
most of the navigation tests are carried out using one of the standard ST imaging light
sources - Schott KL1500 LCD light (as shown in
Figure 20
).
6.3.1 Navigation with bright external light
A 150W halogen light source (with IR filter removed) and light pipe is used to illuminate the
module. The light pipe is held approximately 5cm away.
It is important to test navigation with both slow and fast movements. For the VD5376, the
application note
AN3217:
Interfacing to the VD5376 optical navigation device
(017529)
describes how to improve sunlight navigation. In the VD5377 there has been a sunlight
mode added.
Figure 20. Schott light
6.3.2 Auto-movement
Auto movement (shadow movement) is similar to hover, except that the tests are done in
bright sunlight and the object can either be very close to the module or a distance away.
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AN3419 Revision history
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7 Revision history
Table 3. Revision history
Date Revision Changes
04-Oct-2011 1 Initial release.
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