Today, it is very easy to build our dream projects within the stipulated time, because almost all supporting components & circuits are readily available in pre-wired and compact modules. A short tour through ebay (or amazon) will bring the items at our doorstep within days. “DC to DC Converter Step Up 1.5 Volt to 5 Volt” is one such item I often purchased from online stores. With an input voltage of 0.9V to 5V DC, the module gives a stable 5V DC output through its USB socket. Using two AA batteries we can expect an output current of 500 to 600mA, and a single AA battery gives output current about 200mA. The conversion efficiency is upto 96%.
Last week, when inspired by the irresistible temptation to learn what is behind this wonderful module, I jumped into my circuit surgery lab (at midnight) with one module in my hand. Interested readers can follow this article to know more about my findings!
The module comprises of two capacitors (C1-C2),one resistor (R1), one inductor (L1), one rectifier diode (D2), one LED (D1), and an IC (U1). All of these components are in SMD form, except the USB ‘A’ female socket. Observed values of the components are:
C1: 100nF (Input Filter)
C2: 100uF/16V (Output Filter)
L1: 470 (47uH Inductor)
D2: SS14 (Schottky Diode)
D1: Red LED (Input Power Indicator)
R1: 102 (1K Resistor- LED Current Limitor)
U1: E5 0P (smd marking code… what is the actual part number?)
Blueprint of the internal circuitry is shown here. Note that R1 in the circuit is the traditional current limiting resistor for D1, and the R1+D1 combination (not drawn in the blueprint) is connected across the input supply points, ie across capacitor C1.
Working of this minuscule DC-DC Boost converter module is based on
PFM (pulse frequency modulation) technique. Pulse-Frequency Modulation
(PFM) is a modulation method for representing an analog signal using
only two levels (1 and 0). It is analogous to Pulse-Width Modulation
(PWM), in which the magnitude of an analog signal is encoded in the duty
cycle of a square wave. Unlike PWM, in which the width of square pulses
is varied at constant frequency, PFM is accomplished using
fixed-duration pulses and varying the repetition rate thereof.
A PFM converter is an alternative DC/DC power-converter architecture
that uses a variable frequency clock to drive the power switches and
transfer energy from the input to the output. Because the drive signal’s
frequency is directly controlled to regulate the output voltage, this
architecture is referred to as pulse-frequency modulation (PFM). DC/DC
converters with constant-on-time or constant-off-time control are
typical examples of the PFM architecture.
Since the IC (U1) is an smd chip labelled with an unusual marking code, it’s very hard to figure out (atleast for me) the actual part number of the device. Fortunately, an extra-long journey through internet helped a lot!
First PFM chip found with similar pin assignment of U1, is A7530, which is a CMOS-based PFM step-up DC-DC converter available in SOT-23, SOT-25, and SOT-89-3 package. Only three external components are necessary for this chip (an inductor, a Schottky diode and an output filter capacitor), and the output voltage can be adjusted from 2.5V ~ 6.0V (in 0.1V step). A 7530 in SOT-89-3 package is good for building the exact replica of the PFM module.
Here is the application circuit diagram of A7530 (A7530K3R-XXY series)
from AiT Semiconductor Inc. Type & Value of CINis not very crucial,
but a tantalum-capacitor is mandatory as COUT.
Second chip is S-8353/8354 series from Seiko Instruments Inc. The
S-8353/8354 series is a CMOS step-up switching regulator which mainly
consists of a reference voltage source, an oscillation circuit, power
MOSFET, an error amplifier, a phase compensation circuit, a PWM control
circuit (S-8353 Series) and a PWM / PFM switching control circuit
(S-8354 Series). The S-8353/8354 series can configure the step-up
switching regulator with an external coil, capacitor, and diode.
Today, almost all components are available in SMD version too, and even
an average hobbyist can collect (and handle) them without too much
difficulty. So, if you are in a plan to fabricate your own DC-DC Boost
converter PFM module, I am sure, this article will expedite the
construction process-from concept to completion
Nowadays, single-color and multi-color flashing LEDs are easily
available, which obviates the requirement of external chips to produce
fascinating lighting effects. What can we do with one piece of such a
single color flashing LED, and two pieces of multicolor flashing LEDs?
Here is an ultrasimple circuit of an LED Globe wired around the
evergreen timer chip IC 555. One advantage of this LED Globe is that it
is a voltage-controllable flashing device, ready to work together with
any microcontroller chip. This allows you to control the light pattern
to a certain extent in tune with the output signal from an external
microcontroller, too!
Schematic of the Multicolor Flashing LED Circuit
LM555 datasheet
Nothing new, here the 555IC (IC1-LM555) is wired as a monostable multivibrator (MMV) working on regulated DC5V supply. RC components R2(1K) and C2 (100uF) sets the monotime period. At the front end of the circuit, one single-color flashing LED (LED1-5mm Red) is connected across the power rail through a current limiting resistor (R1-1K). The pulse output available from this LED is directly fed to the trigger input (pin 2) of the 555 IC. The control voltage is driven to the control voltage terminal (pin 5) of IC1 through a resistor (R4-1K). For normal use, the control voltage can be generated from a 10K multi-turn potentiometer (P1-10K) as shown in the circuit diagram. Actually, any kind of DC voltage level generator can be used to control this circuit. It could come from a photoresistor voltage divider, sound to voltage converter,from a microcontroller,etc etc. The IC1 output (from pin 3) is then extended to two 5mm multi-color flashing LEDs (LED2&LED3) through a single current limiting resistor (R3-47R).
As you may well know, 555 IC turns on when its pin 2 is below 1/3VCC,
and turns off when its pin 6 goes above 2/3VCC. These levels can be
shifted either higher or lower than the nominal levels by applying a
voltage at its pin 5. For example if we apply a higher +ve voltage, the
turn off threshold is higher than the normal 2/3VCC. This trick is used
in this circuit to produce pleasing (and fairly unpredictable) light
patterns from the three LEDs. Try to enclose the finished circuit in a
translucent globe for better attraction. Or try an artistic arrangement
with the help of suitable light diffusers!
Test Report
During testing, pulse reached at pin 2 of IC1 is of 1.2Hz frequency with near 47% dutycycle. The voltage swinging is in 1.4V to 2.1 V range (not very accurate measurement)
Voltage available at pin 5 of IC1 is from 0.8V (P1 fully counter clockwise) to 4.5V (P1 fully clockwise)
When P1 is in fully counterclokwise , LED2 is ON and LED3 is OFF. When P1 travels beyond its mechanical centre position LED3 also turned to ON state. When P1 is in fully clockwise, both LEDs are in ON state but now with a different pattern. Amazing visual effects created by the three LED combination is very difficult to describe in detail. Get ready to watch it yourself !.
This usb car charger was designed with the aim of providing an onboard usb power outlet for charging/running portable usb devices. This circuit is an improved version of the usb power socket circuit published years ago in Electronics For You. At the time, this was designed around a step-down linear regulator chip. The aim of the present design, based on a step-down switching regulator chip, is to create a usb power outlet that has more efficiency which can cope with higher current requirements, so that it also becomes suitable for more powerful standard usb devices and non-standard usb decorations. A switching voltage regulator is a handy weapon in the battle to reduce heat dissipation in circuits. The buck-converter chip in this circuit can handle input voltage up to 40 V, and can deliver an output current of up to 3 A. Note that the circuit is principally designed for use with an in-dash cigar lighter socket, because this mode of operation is particularly practical in automobiles.
Schematic of the USB Car Charger Circuit
LM2596 datasheet
Circuit Description
The DC voltage delivered by the car battery is routed to the input
socket (J1) of the circuit through the indash cigar lighter power
socket. The fuse (F1) and diode (D1) are wrong polarity/overcurrent
circuit protection components and the capacitor (C1) is a smoothing
element. When on/off switch (S1) is turned to its on position, this
input supply is extended to the rest of the circuit, and the power input
indicator (LED1) lights up.
The switching regulator (buck converter) circuit is built around the
LM2596,and is mostly based on the design given in the device’s
datasheet. The LM2596 series of regulators are precision monolithic
integrated circuits that provide all the active functions for a
step-down (buck) switching regulator, capable of driving a 3A load with
excellent line and load regulation. These regulators operates at a
switching frequency of 150 kHz thus allowing smaller sized filter
components than what would be needed with lower frequency switching
regulators.
Here, the 5V fixed output version LM2596T-5.0 (IC1) is used as the
switching regulator. Note that the output available is highly dependent
on the quality of inductor (L1) and output capacitor (C3). For the
inductor, the dc current and resistance ratings are critical in addition
to its inductance. For the capacitor, a low ESR is essential. The green
LED (LED2) is the power output indicator. Stable 5V dc output from IC1
is branched into two usb outputs, named DP (Decoration Port) and DCP
(Dedicated Charging Port). DP port can be used to run non-standard usb
gizmos like usb reading lamp, heater, fridge, etc. The DCP is reserved
only for charging standard usb devices including smart phones and
tablets. The jumpers JP1 and JP2 are reserved for circuit enhancements.
By default, pins 2&3 of JP1 and JP2 are bridged independently for
standard operation. Infact, jumper JP1 can be used to add special
features like under-voltage lock out (UVL), and JP2 can be used to carry
out some usb trickery!
Components List
- IC1: LM2596T-5.0*
- D1: 1N5408
- D2: 1N5824*
- LED1: 5mm Red
- LED2: 5mm Green
- L1: 33uH/3Amp* – Designed for National’s 150KHz Simple Switcher
- C1: 100nF
- C2: 470uF/25V* – Low ESR Aluminium Electrolytic Capacitor
- C3: 220uF/25V* – Low ESR Aluminium Electrolytic Capacitor
- R1: 1K ¼ w
- R2: 470R ¼ w
- S1: SPST on/off switch
- J1: DC socket
- J2-J3: USB (A) sockets
- F1: 4Amp Fuse (test selected
USB Charging
According to the USB Battery Charging Specification, a device plugged
into a USB port to charge may find itself connected to a source that is
capable of data transfer as well as power, or it may be connected to a
source that provides power only. If the source supports data, the device
is expected to do a trickle charge only, but if the source does not
support data, the device may draw more current because the source is
likely to be an ac adapter. So if you want to charge your smart phone as
fast as possible with the USB car charger, it may become necessary to
join the usb data pins together, which is the spec-compliant way to
indicate that the usb power source does not support data (more details
available on Wikipedia).
Construction
Building up the usb car charger should not present undue difficulties if
you follow the components list and (ofcourse) the datasheets of crucial
components used. It is recommened to build the system on a small
circuit board. Having verified the circuit works properly, you are ready
to fit the wired circuit board in a suitable enclosure with the
suggested front panel. The enclosure may be finished to individual
taste.
Crosscut
Readymade DC-DC Buck Converter modules, based on the adjustable version
of LM2596, are cheaply available through many online stores. With the
help of an onboard potentiometer, it is possible to adjust the output
voltage from 1.25V to 35V dc.
While the 555 oscillator IC is a very versatile device, it can also be quite tricky and solutions are not always obvious. Such is the case with this edge-triggered 555 monostable circuit. By differentiating the trigger signal, the monostable multivibrator times out normally regardless of the trigger signal length.
555 Schematic
555 datasheet
More than a capacitor
The classic differentiator circuit consists of a capacitor and resistor. In this way, the positive change in the trigger signal is coupled to the 555 via C2. When the trigger signal eventually resets, D2 is required to prevent the change in voltage from creating a substantial negative spike. While a negative transient of this nature is unlikely to cause damage, it could well cause temporary IC malfunction.
R-C timing circuit
C1 and the series resistance of R1 to R3 affect the timeout function. Circuit values may be selected per application requirements. This part of the circuit is fairly typical.
Driving the relay
The 555 output is virtually always in the incorrect polarity. However in this case, the relay is working against the positive 12V rail so its operation is effectively inverted. Note the clamp diode that is across the relay coil.
Oscillographs
Photos
About the test circuit
To generate a trigger signal, I used a miniature pushbutton that works against Vcc. The relay contacts are connected to drive an LED.
SCRs are the switching devices for this unusual DC to DC converter that is suited for the ubiquitous 5V USB power source as well as numerous other applications. This novel power circuit topology uses an intermediate resonant link that facilitates self-commutation for both SCRs – while SCRs are easy to turn on, they tend to be difficult to turn off in DC applications. This discussion covers primarily the relatively complex control circuitry -the power circuit and theory were previously covered in this article:
SCR DC to DC converter. All circuitry consists of discrete components and should be relatively easy to simulate.
Schematic of the 12V to 5V USB Converter Circuit
Not for the novice or fainthearted
Getting this to work took all my expertise. Fortunately, you can
benefit from this published work, but be assured that it cannot work
unless EVERYTHING is in order simultaneously –that is why I cannot
accept the absurd theory of evolution (incredibly complex life forms
developed and optimized by themselves…).
The occasion for this design
It seems that in the Philippine Islands, there is one tough
electronics instructor who seems to have a penchant for thyristors. One
assignment given to his students was to come up with a solar charge
control and USB power supply regulator using SCR power devices.
Eventually, this request filtered down to me via electroschematics.com.
Perhaps some wondered how I came up with the unorthodox idea for the SCR
solar charge controls previously posted. At first, I thought this was
crazy, but eventually realized that he was simply attempting to get his
students to stretch their minds, attempt to think outside the box and
realize that there are numerous means of solving virtually any problem.
For me it has been a challenge and lots of fun.
SCR drivers
Two programmable unijunction transistors (PUTs) are employed to drive
the SCR gates. The PUT is well suited for driving the primary of a
pulse transformer. A 0.01uf capacitor discharged into the primary of the
1:1 pulse transformer is sufficient to generate a 70mA, 20uS gate
pulse. In observing the gate pulse oscillograph, it can be seen that the
relatively slow gate pulse rise time leaves something to be desired
—this is the result of transformer leakage inductance caused by poor
primary to secondary magnetic coupling.
Control Algorithm
SCR1 fires when DC output < 5V, AND SCR1 is forward blocking, AND 70uS time delay has elapsed.
SCR2 fires when SCR1 is reverse blocking, AND 70uS time delay has elapsed.
Implementation of this algorithm results in operation much like a
well-timed sewing machine. The delay function is required to provide
sufficient time for the thyristors to commutate –according to the
specifications on this particular device, turn-off time is 50uS. Many
power devices do not have a turn off time (Tq) specification.
How it works
For firing SCR1, the minimum delay time is a function of the charging
of C8 –this delay is extended by the effect of the voltage regulator.
D3 is the TI TL431 adjustable shunt voltage reference that is strapped
for minimum (2.5V). Q7 compares this reference voltage to the feedback
voltage through the feedback voltage divider that consists of R16 &
17. Q6 both inverts the feedback signal and references it to common
potential so that it may shunt C8. Q5 turns on when there is voltage
across the capacitor network –it essentially tells the firing circuit
that the capacitor network is empty and needs a new charge. Q5 & 6
also form an AND function so that both conditions must be satisfied
before C8 is allowed to charge. When C8 charges to approx 8.6V,Q8 fires
and triggers SCR1. SCR1 subsequently charges the capacitor network and
does not stop at 12V because at that point the inductor is fully charged
and must keep conducting until the capacitor network voltage reaches
approx 24V.
When the voltage across the power supply output reaches 1.2V, Q6
turns on and shunts the gate of Q10 thus turning off the startup timing
capacitor. Q6 also turns on under short circuit conditions thus limiting
short circuit current.
For firing SCR2, Q4 is the firing circuit. When the voltage across
the capacitor network exceeds 12V, Q1 turns on, Q2 turns on and C10 is
allowed to charge –at this point, the 70uS timing period commences.
Actually, SCR1 does not block until L1 is fully discharged, but it will
happen after another quarter-cycle of the resonant tank elapses (16uS).
This allows another 54uS to elapse before SCR2 can fire and that
satisfies the turn-off time spec for SCR1 (Tq).
Specifications
- Output voltage: 5V (may be trimmed by varying R17)
- Voltage regulation: Approx 1% no load to full load
- Response to load voltage changes: Immediate
- Output current: 500mA
- Efficiency @ FL: 55% (higher at 14V input voltage)
- Short circuit current: 1.3A (may be continuous without damage)
- Current limit: Not measured, but exceeds 1.3A
Output capacitor
C7 must be a low ESR (Effective Series Resistance) type, or must
consist of parallel devices in order to reduce output voltage ripple.
The Panasonic device recommended on the schematic is a potential
candidate. The capacitance may actually be much greater than 1000uf
without issues.
Bugs encountered
All issues involved the SCR1 driver. Initially, it would not wake up
with a load connected. This was traced to SCR discharging the resonant
tank into essentially a short circuit because the voltage across C7 was
very low. At this point, the free wheeling current flowing through D1
kept SCR2 alive until the subsequent firing of SCR1. This resulted in
both SCRs conducting simultaneously —not a good situation because it
causes the load voltage to approach 12V when it is supposed to be 5V.
This was corrected by adding C9 to delay the turn-on of SCR1 by about
240uS —normally it is about 70uS. The low voltage conditioning circuit
consisting of Q9 & Q10 senses when the load voltage is less than
1.2V —below this voltage, Q10 is connected in parallel with C8 thus
delaying the SCR1 firing circuit. When the voltage exceeds 1.2V, C9 is
disconnected and the timing becomes normal.
The second bug involved latch up of Q8 —this was apparent when the
12V power input was teased (very severe and aggravating condition). This
caused the output voltage to die and would not restart. This was solved
by removing the back diode that was connected across the primary of T2,
and reducing the impedance of the Q8 gate bias network that effectively
increase the valley current (reset threshold) of Q8.
With these issues corrected, operation was extremely reliable and robust.
Conclusions
While it works great, this busy circuit is definitely not a preferred
solution. The efficiency is not that great (55%) –perhaps it can be
further optimized. However, it is a great experimental circuit that will
expand the experimenter’s knowledge in many areas. On the other hand,
there may just be a niche application where this circuit is a good
solution.
Acknowledgement: Thanks to RencoUSA Inc., Sanford FL, for samples of
the mini-drum inductor (RL-5480-4-22). I have always appreciated their
excellent support and competitive prices.
Photos
Observe how much the circuit changed from the original concept.
This took up the entire length of the protoboard –busy circuit!
Check out the LEM current transducer that I use for measuring current
–the current is actually inductor current rather than capacitor
current. The inductor current includes the free-wheeling current through
D1.
For the future
- High voltage SCR DC – DC applications
- LED Chaser firmware
- What is the difference between an operational amplifier and a comparator
Amplification is the process of increasing the amplitude of a AC signal
current or voltage such as audio signal for sound or video signal for a
television picture. The amplifier allows a small input signal to control
a larger amount of power in the output circuit. The output signal is a
copy of the original input signal but has higher amplitude.
Amplification is necessary as in most applications, the signal is too
weak to be used directly. For example, an audio output of 1mV from a
microphone is not able to drive a loud speaker which requires a few
volts to operate. Hence, the signal need to be amplified to a few volts
before it can be fed into the loud speaker.
NPN Transistor Circuit Configuration
An example of different type of transistor configurations in the circuit is as shown in Figure 1 below.
- The common emitter(CE)
circuit uses emitter as its common electrode. The input signal is
applied to the base and the amplified output is taken from the
collector. This is the one generally use because it has the best
combination of current gain and voltage gain.
- The common base (CB)
circuit uses base as its common electrode. The input signal is applied
to the emitter and the amplified output is taken from the collector. The
relatively high emitter current compared to the base current results in
very low input impedance value. For this reason, the CB circuit is
seldom used.
- The common collector (CC)
circuit uses collector as its common electrode. The input signal is
applied to the base and the amplified output is taken from the emitter.
This circuit is also called an emitter follower. This name means that
the output signal voltage at the emitter follows the input signal at the
base with the same phase but less amplitude. The voltage gain is less
than 1 and is usually used for impedance matching. It has high input at
the base as a load for the preceding circuit and low output impedance at
the emitter as a signal source for the next circuit.
Classes
They
can be classified into classes A, B, C and AB. They are defined based
on the percent of the cycle of input signal that is able to produce
output current.
In Class A, the output current flows for the full
cycle of 360 degree of input signal. The distortion is the lowest with
around 5% to 10% and an efficiency of 20% to 40%. In general, most small
signal operate class A
In Class C, the output current flows for
less than one half of the input cycle. Typical operation is 120 degree
of input current during the positive half cycle of the input current.
This class has an efficiency of 80% but has the highest distortion. This
class is usually used for RF amplification with a tuned circuit in the
output.
In Class B, the output current flows for one half of the
input cycle which is around 180 degree. Class B operation lies between
class A and class C. Class B are usually connected in pairs and in such a
circuit called push-pull amplifier. The push-pull is often used for
audio power output to a loud speaker.
In Class AB, it offers a
compromise between the low distortion of class A and the higher power of
class B. It is usually used for push-pull audio power amplifiers.
Robotics is the branch of technology that deals with the design,
construction, operation, and application of robots, as well as computer
systems for their control, sensory feedback, and information processing.
The word robotics comes from Runaround, a short story published in 1942
by Isaac Asimov. Robot is an electro-mechanical machine that is guided
by a computer program or electronic circuitry.
A robot system contains sensors, control systems, manipulators, power
supplies and software all working together to perform an assigned task.
One of the most basic autonomous robot you can build is a line
following robot(LFR). The purpose of this AVR tutorial-part 23 is to
help you build a Line Following Robot using an inexpensive AVR chip,
that can follow an arbitrary path!
LFR-Overview
Our LFR is fairly a good line follower robot, consists of low-priced
electro-mechanical parts, electronic components, and a microcontroller
chip-based processor circuitry. Bare essentials are listed below:
- Robot Chassis
- Robot Motors
- Caster Bullets
- Robot Wheels
- IR Sensor Cards
- IC L293D
- IC Atmega8
- Motor Clamps, Switches,B attery Holders, Batteries, Small Electronic Components, Screws & Nuts, etc.
The line follower logic can be divided into two (sensing and
controlling) segments. At first, LFR logic observes the track pattern
ahead. In the second phase, the logic operates two drive motors (left
and right) as per the informed track status. The infrared sensor card
contains infrared light emitting diodes and infrared photodiodes.
The dual-channel motor controller is a simple H-Bridge driver chip
L293D. Brain of the line follower robot is one Atmega8 microcontroller.
LFR-Mechanical Assembly
First of all attach motors, clamps and wheels as illustrated here.
Next, attach two caster bullets (front and rear) at the bottom of the
chassis. Finally, drill suitable holes in the chassis to fit all
remaining parts such as finished circuit board, sensor cards, battery
holder, pcb spacers, supporting clamps, etc.
The battery holder can be fitted at the rear-top of the chassis, just
near the caster bullet. Best location for main circuit board is the
centre-top of the chassis. The infrared sensor cards (left and right)
should be fitted at the front-side of the chassis, in downward
direction, so that infrared sensor components (light sender and
receiver) can comfortably catch the underneath path.
Take a note, our LFR follows a path with black track on white surface.
To sense the track properly, infrared sensors must be placed on the
chassis in such a way that they are very close to the track level.
Ensure that distance between two infrared sensor card (left and right)
must be 3 to 6mm greater than the width of the marking on the track.
LFR-System Logic
As described earlier, our LFR is a simple robot which will follow a
black line on a white background. This AVR chip-based LFR has a very
simple logic, discussed below using if-else in the pseudo code.
IF (Left side of the LFR is about to touch the left side of the track)
Turn Right;
ELSE IF (Right side of the LFR is about to touch the right side of the track)
Turns Left;
ELSE
Move Forward;
If both infrared sensors (left and right) are on the white surface,
the LFR will move forward, and if both sensors are on black surface, the
LFR will stop. When the left sensor is on white and right sensor is on
black, LFR will take a right-turn. Similarly, when the right sensor is
on white and left sensor is on black, LFR will take a left-turn. These
four cases are the only possible conditions for a basic line follower
robot.
LFR-IR Sensor Card Circuit diagram
Our LFR has two infrared sensor cards (left and right) on the bottom
of the chassis for detecting the black tracking indicant on the path.
Each sensor card is a combination of an infrared LED, infrared
photodiode, and a comparator chip works on 5V DC supply. The comparator
circuit is wired using one-part (½) of the LM358 IC.
In the default jumper condition (JP:1+2), output of the infrared
sensor card is at a logic-low (L) state, when it detects a black color,
and vice versa. Remember, we need two identical infrared sensor cards;
one for left side, and other one for right side!
→ Part 24: To be concluded in next part
Today almost every mobile phone contains a camera. In principle,
mobile phone camera is a sensor/camera module designed for use across a
range of mobile phone handsets and accessories. It embeds high quality
still camera functions and also supports rich video. For these camera
modules designed to work with any host with a standardized camera
interface, separate hardware accelerator device (coprocessor) can be
integrated in the mobile phone system to run the associated image
processing algorithms in hardware where the baseband cannot support this
processing load.
Or these camera modules can be directly connected to a baseband or
multimedia processor. No dedicated coprocessor is required in the second
configuration because the image processing is done in software (or
hardware) within the baseband processor. Ofcourse, you can take these
cameras from mobile phones and inteface them yourself with your advanced
hobby electronics projects just as with any other standard add-on
modules. However, good knowledge in popular camera interface techniques
is a prerequisite to proceed with your succeeding dream project.
Behind The Camera Interface
Because the companies that make mobile phone cameras and the
companies that make the application processors are usually different,
there is a need for standardization of the camera/application processor
interface. MIPI (mobile industry processor interface) Alliance has been
on top of this, and the main connection is a fast serial interface known
as CSI (camera serial interface).
The mobile phone handset industry had a need for a standard interface
to attach camera subsystems to a host device, such as an application
processor. In response, MIPI developed CSI2 several years ago. The
Camera Working Group – develops and maintains camera serial interface
and supporting documents – released the CSI-2 v1.0 specification in
2005. The group produced CSI-3, a next generation interface
specification based on the MIPI foundation of UniPortM, in 2012.
CSI-2 consists of a DPHY and a CSI-2 transmitter at the camera and
receiver on the application processor. The DPHY provides the physical
interface, and the transmitter and receiver cover encoding, packing,
error handling, lane distribution, assembly of image data stream, etc.
However, the increasing pixel count and frame-rate is driving the need
for even higher bandwidth, hence CSI-3. CSI-3 has a new MPHY, and each
MPHY has a bandwidth of up to 6Gb/s per lane, with up to 4 lanes. The
next level up is the Unified Protocol layer (UniPro). This defines a
unified protocol for connecting devices and components designed to have
high speed, low power, low pin count, small silicon area high
reliability and so on.
CSI-2: The “Camera Serial Interface2 Specification”
defines an interface between a peripheral device (camera) and a host
processor. The host processor (baseband, application processor) here
denotes the hardware and software that performs essential core functions
for telecommunication or application tasks. Two high-speed serial data
transmission interface options are defined. The first option – referred
to in this specification as the “DPHY physical layer option” – is a
unidirectional differential interface with one 2-wire clock lane and one
or more 2-wire data lanes. The physical layer of this interface is
defined by the MIPI Alliance Specification for DPHY. The second
high-speed data transmission interface option, -referred to in this
specification as the “CPHY physical layer option”- consists of one or
more unidirectional 3-wire serial data lanes, each of which has its own
embedded clock. The physical layer of this interface is defined by the
MIPI Alliance Specification for CPHY. The Camera Control Interface (CCI)
for both physical layer options is a bidirectional (SDL-SDA) control
interface compatible with the I2C standard.
CSI-3: This interface technology is much easier to
implement in both hardware and software than the existing technologies.
CSI-3 is a new standardized data and control interface between the
camera subsystem and the host device. Note that, within a camera
subsystem, various components such as a RAW camera sensor, an SoC
(system – on a – chip) camera, or a multi-chip camera module can be
connected to each other using a proprietary interconnect, or CSI-3.
The VX6953CB Camera Module
The VX6953CB 5.1 megapixel EDOF (Extended depth of field) camera
module (from ST) is designed for use across a range of mobile phone
handsets and accessories. It embeds high quality still camera functions
and also supports HD video. VX6953CB produces raw Bayer 5 Mpixel images
at 15 fps in RAW10, and supports the CCI control as well as CCP 2.0 and
CSI-2 (D-PHY v1.0 compliant) data interfaces. As stated, the VX6953CB
has both CCP2.0 and MIPI CSI-2 video data interfaces selectable over the
camera control interface (CCI).
The image data is digitized using an internal 10-bit column ADC. The
resulting pixel data is output as 8-bit, 10-bit or 10-8 bit compressed
data and includes checksums and embedded codes for synchronization. The
interface conforms to both the CCP 2.0 and MIPI CSI-2 interface
standards. The sensor is fully configurable through a CCI serial
interface. The module is available in a SMOP (small optical package)
type package measuring 6.5 x 6.5 x 4.6 mm. It is designed to be used
with a board-mounted SMIA65 (standard mobile imaging architecture)
socket or flex cable.
Pinout and pin description of VX6953CB camera module, as viewed from the
bottom of the module, is shown below. In the pinout table, note that
pads T1-T8 are ST Test Points.
Since only a minimal list of external components is required, the
VS6953CB features allow straight forward integration into
custom-designs. VS6590 is another near-similar camera module from ST,
but with only 0.5 Megapixel resolution (800Hx600V)and CCP 1.0 serial
video interface.
- CCP → CCP stands for Compact Camera Port, the
interface standard for portable cameras, developed by SMIA (standard
mobile imaging architecture) -an organization promoting the
standardization of mobile phone (cellphone) interfaces.
- CCI → This is usually a two or three-wire interface
used to control the sensor module. Though named differently by
different vendors (e,g. Serial Camera Control Bus, SCCB by Omni Vision),
it usually confirms to the I2C standards (defined by Philips).
- SMIA → SMIA (Standard Mobile Imaging Architecture)
is an imaging architecture especially suitable for mobile application
use. The scope of SMIA covers a raw bayer output image sensor head: It
specifies housing, mechanical interconnection, functionality, register
set and electrical interface
In the next figure, you can see the camera wiring in a Nokia 2700C
(Nokia 2700c2 RM-561) mobile phone circuitry. In the schematic diagram,
the 12-pin camera connector is labelled as X3300. The camera module can
be safely removed from this connector/socket using a special “Nokia
Camera Remover Tool”, available as a service accessory. For more
details, refer the official service documentation/service schematics
published by NOKIA™.
Referenced Documents (including but not limited to):
- MIPI Alliance Standard for Camera Serial Interface 2 (CSI-2) v1.0
- MIPI Alliance D-PHY Specification (v00-90-00)
- High-Speed interface Technology for Image Data Transmission (FIND Vol.26)
- Camera Sensor Driver Development and Integration (PATH PARTNER)
- SMIA 1.0 Introduction and Overview (NOKIA & ST)
- Arasan’s White Papers & Articles
Part 2 → Mobile Phone Camera and Arduino/Raspberry Pi
