Theory, Technical Aspects and Upgrading Possibilities of the Component Tester

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Theory, Technical Aspects and
UpgradingPossibilities of the Component Tester
this year's Club Construction Project
With G4FDN, G4FYF, G8MNY possibly G4XAT
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A Idea!

• Suggested by Steve G4FYF
• .but it come out of a search for a bezel or case
  for the DDS project that had been discussed on
  the Top Band net, and then via email.
• Steve found a bezel from Hobbytronics at 2.28
  and then after searching myself, I found a
  project case with LCD cut out from Bang good for
  1.65, as I had used them previously.
• Steve then looked on Bang good himself and found
  the LCR Transistor kit the case was intended for.
• He went and bought one, constructed it and it was
  suggested to committee that this be this years
  construction kit.

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Chinese production..but German
ingenuity

• As the kit was based on the ATMEL ATMega328
  microcontroller the same as used in the Arduino,
  I searched and found who it was designed by
• Karl-Heinz Kuebbeler but it was based on the
  earlier design of
• Markus Frejek who published an article titled
  AVR-Transistortester,. In the Embedded Projects
  Journal, 11. Ausgabe, 2011
• The project is ongoing in terms of S/W H/W
  development.

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This is what the kit looks like .
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Tester Specification

• Resistance 0.1O 50MO
• Capacitance 30pF 100mF
• Inductance 0.01mH 10H
• ESR 0.01O upwards for capacitors 2uF or greater
• PNP and NPN type bipolar transistors
• N P channel MOSFET, JFET FETs
• diodes including forward voltage drop , two
  diodes, LEDs
• thyristors (automatic detection pin definitions)
• measurement of the bipolar transistor current
  amplification factor (B) and conduction voltage
  emitter junction (Uf).
• Darlington transistors can be identified by the
  amplification factor of the high threshold
  voltage and high current.
• Internal protection diodes inside bipolar
  transistor and MOSFETs can be detected and
  displayed on the screen.
• threshold voltage and MOSFET gate
  capacitancePotentiometers (variable resistors)
• Each test time is about two seconds, only large
  capacitance and inductance measurements will take
  a long time. Standby current 0.02uA, operating
  current 25mA.

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Tester Circuit Diagram
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Main Circuit Areas

• Power supply and regulation
• Functional control
• Display
• Clock oscillator
• Precision voltage reference
• Input/output
• connection of components
• Test control

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AVR ATMega328 Architecture
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By the software programmed into it, it
providesFunctional controlDisplay
controlInput/Output definition and
connectivityClock and frequency
definitionAlgorithmic determination and
calculation
The ATMega328 microcontroller
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A closer look at input/output

• An I/O port is a pin on the microcontroller that
  can be set to
• Input or output
• Digital or analogue
• Simply put, the assignment of the pin and its
  function is achieved by the definitions in the
  program loaded into it.
• Where a pin is defined as an analogue input, it
  will have an Analogue to Digital Converter
  associated with it

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Analogue Digital Converter

• An ADC will convert a voltage to a binary number.
  
• The maximum voltage is usually determined by the
  supply voltage of the microcontroller.
• The range of steps between the minimum and
  maximum voltage is determined by the number of
  bits or resolution of the ADC. The ATMega328
  has a 10 bit ADC and therefore 1024 possible
  values between min and max, e.g. 2.5v represented
  by 512 decimal or 1000000000 in binary

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A simplified 3-bit ADC
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Measuring and determining components
Typically, say to measure a resistance, we
connect a known resistance in series with an
unknown, then apply a known voltage and determine
the value of the unknown resistance by voltage
division.
So if R1 is known and R2 is unknown, then Vdiv
Vin x R2/(R1 R2) R2 Vdiv x (R1 R2)/Vin
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Continued..
This can be expanded to capacitors and inductors
by recognising that the reactance of them is
proportional to frequency, with capacitors it
decreases with frequency, and with inductors it
increases with frequency, or we can use the time
constant method where we apply a known
voltage/current and time how long it takes to
reach a particular percentage of that applied.
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Capacitance determined by time constant
So C R/t when voltage across C is 63 of V
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What the I/O ports look like
The PUD switch isolates all pull up" resistors
of the ATmega328. The output of a pin can be
switched off with the DD switch. The Input can
operate regardless to the state of the switch DD.
The PORT switch usually defines the output level,
but also switches the pull up resistor. Because
the PORT and DD sitches can not be changed at the
same time but only one after another, the pull up
resistors can disturb the measurement. Therefore
in the program these are disabled with the PUD
switch.
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Cont
Every test pin (measurement port) can be used as
a digital or analogue input. This measurement
capability is independent of using the port as
output. Every test pin can be switched to output
and in this mode it can be directly connected to
GND (0V) or VCC (5V), or it can be connected via
a 680 resistor or a 470k resistor to either GND
or VCC. Table 5.1 shows all possible combination
of measurements. Notice, that the positive state
can be switched directly to VCC (Port C) or it
can be connected with the 680 resistor to VCC
(Port B). The same possibility has the negative
state of terminal probe to the GND side. The test
state means, that the probe can be open (Input),
connected with the 470k resistor to VCC or GND,
or that the probe can be connected with the 680
resistor to VCC or GND.
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Possible Pin Combinations
NB positive means connected to VCC
(5V), Negative means connected to GND (0V)
Every test pin (measurement port) can be used as
digital or analogue input. This measurement
capability is independent of using the port as an
output. Every test pin can be switched to output
and in this mode it can be directly connected to
GND (0V) or VCC (5V), or it can be connected via
a 680 resistor or a 470k resistor to either GND
or VCC. The table above shows all possible
combination of measurements. Notice, that the
positive state can be switched directly to VCC
(Port C) or it can be connected with the 680
resistor to VCC (Port B). The same possibility
has the negative state of terminal probe to the
GND side. The test state means, that probe can be
open (Input), connected with the 470k resistor to
VCC or GND, or that the probe can be connected
with the 680 resistor to VCC or GND.
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So putting this together ..

• The program loaded into the microcontroller
  applies an algorithm (a set of rules to solve a
  task or problem) which in its simplest sense
  boils down to
• Identifying the type of component
• Measuring the parameters applicable to the
  component.
• It does this by applying conditions at the three
  pins/ports as per the table. The measurements
  obtained determine what if anything is connected
  to which pins.

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An example.
A diode connected to pins 1 2, would test as an
open circuit between pins 1 3, 3 1, 2 3, 3
2. It would have a low forward resistance say
between 1 2 but a high resistance between 2
1. It would have also have a non linear V/I
characteristic, with an approximate constant
forward voltage drop e.g. around 0.2V for
Germanium, and 0.6V for Silicon. By going
through a predetermined hierarchy of tests, with
an algorithm for a each type of component, by a
process of elimination it is possible to identify
the type of component and its value(s).
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The software

• Is open source, freely available
• The Bang Good tester uses an earlier version
• The software is configurable to allow additional
  features, or remove ones not required.
• You need a freely available compiler and a cheap
  programmer to update the S/W

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Accuracy

• The main h/w components affecting accuracy are
• Resistors R1 to R6 i.e. 680R and 470k
• The LM336 2.5V voltage reference
• These can be selected on test and/or replaced
  with higher precision components if one so desires

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Physical construction
Over to Steve G4FYF, John G8MNY Gareth G4XAT