A Useful Test Tool in the form of Advanced Test Tweezers
Version 2.0 Date 1 Aug 23
Necessity is the Mother of Invention so when the need arose to measure small capacitance SMD components, a project in the Silicon Chip February 2023 caught my eye: A set of Advanced Tweezers to test R, C, D components, a voltmeter, a limited CRO, a UART decoder, a I/V plotter and a tone generator. I scoured the list of capabilities but could not find floor mopping, washing or ironing!
Silicon Chip published a “Tweezers” project [ October 2021] to grip SMD components which proved attractive and so the follow-on project gave advanced capabilities.
The attraction is a basic test instrument that can be cradled between the forefinger and the thumb and reveal component data plus more on a small OLED screen. It uses a 28 pin 16 bit microcontroller with a 12-bit ADC giving extra resolution; it has extra RAM and flash memory whilst the display is larger and more readable than earlier models.
One screen displays capacitance, resistance and diode characteristics and goes further on expanding the individual C,R and D characteristics each on a single screen with larger font. Resistance users a voltage divider equation to deduce the measured resistance under test. A constant current source can be used to measure intervals of time and then measure the charge delivered to a capacitor.
It came with Bill of Materials and to make things easy, a kit including all of the small parts, a PCB and a preprogrammed PIC microprocessor. On previous projects, I have spent much time touring the outlets to collect the necessary parts and conclude the most convenient way is to buy a kit: two were ordered.
SiChip published the article over the two months, Feb and March 2023 which gave time to digest the first the operation, the many uses and then the construction phase.
The real challenge comes in successfully soldering the 28 pin SMD microprocessor: lining up the pins using sparing amount of solder and flux, then heating the PIC IC pins until the solder wicks between pcb lands and the PIC. I made two attempts and I used excess solder: I clearly needed to practice my skills so some surplus populated PCBs served as practice trainers to remove and then remount SMDs. Finally, I made sure the PIC was correctly soldered by inspection through a microscope. A caution in restricting the amount of solder paste to prevent the melt rolling into balls and bridging pins. The smaller parts were easy to place with tweezers, a steady hand and a small hand soldering iron.
The OLED is easy to mount as are the other hardware components.
On powering up, the OLED displays one of the many user screens along with a selectable 13 screens of self-calibration. I commend the Silicon Chip Feb and Mar 2023 articles for a step-by-step process to make this very valuable gadget.
A completed example activated in “Volt Meter”mode.
John Baker
VK3JWC
