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