Transcript Getting Going on Digimodes

Theory, Technical Aspects and Upgrading
Possibilities of the Component Tester
–this year's Club Construction Project
With G4FDN, G4FYF, G8MNY & possibly G4XAT
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.
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.
This is what the kit looks like ….
Tester Specification:
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Resistance: 0.1Ω ~ 50MΩ
Capacitance: 30pF ~ 100mF
Inductance: 0.01mH ~ 10H
ESR: 0.01Ω 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 capacitance
Potentiometers (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.
Tester Circuit Diagram
Main Circuit Areas
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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
The ATMega328 microcontroller
By the software programmed into it, it
provides:
Functional control
Display control
Input/Output definition and connectivity
Clock and frequency definition
Algorithmic determination and calculation
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
Analogue Digital Converter
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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
A simplified 3-bit ADC
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
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.
Capacitance determined by time constant
So C = R/t when voltage across C is 63% of V
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.
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.
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.
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.
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).
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
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
Physical construction
Over to Steve G4FYF, John G8MNY &
Gareth G4XAT