Lab Snapshots

by Marek Ples


A few examples

Table of contents

Device for determining the profile of tissue puncture force (μC)
Driver for camera and equatorial telescope mount (μC)
Low voltage Solid State Tesla Coil for use in education (an)
Robot with AAM module - walking flame thrower (μC)
Ionization chamber and 220Ra (an)
Plasmophone - Voice of the Energy (an)
Acoustic levitation (an)
Simple hardware speech synthesizer (μC)
Whiteboard Drawing Robot (μC)

μC - microcontroller project; an - analog project

Device for determining the profile of tissue puncture force

The aim of the work was to develop a construction of a device enabling the registration of the puncture force profile of human or animal tissue with the use of needles used in amniocentesis procedures.

The implementation of the assumed goal required defining the assumptions for the project, then developing the structure and preparing the software and conducting tests. At the beginning prerequisites were set, and they were as follows:

To ensure easy replacement of broken parts, accessibility of components, and compatibility with market-available 3D printers, the entire device was designed accordingly. To achieve these goals, an ATMEGA328p microcontroller from the Iduino Nano board was selected to avoid unnecessary soldering and custom-made parts. The pre-uploaded bootloader was erased from the FLASH memory, and the ISP interface was used for programming with a USBasp programmer. The microcontroller's internal program was written in the BASCOM programming language. To measure the force acting on the needle, two 26x26mm tensometric pressure sensors with a measuring range of 50N were used, along with an HX711 amplifier to gather data for further processing. To counteract thermal drift affecting the pressure sensors, two sensors were used and placed back to back. To measure the depth of the needle, a 3D printed ringed arm was designed and connected to a linear potentiometer. The voltage recorded by the potentiometer changed as the needle penetrated further into the sample, allowing for precise measurement of the depth of the needle tip based on the potentiometer's linear characteristic.

Figure 1 illustrates the construction of the measuring device.

Fig.1 - Measuring device
A - main body with slot for pressure sensors; B - stiffener keeping the needle straight during measurements; C - arm allowing measurement of depth of penetration of needle; D - potentiometer housing; E - back cover

All parts had to be designed in a way that would allow the entire device to co-work with a Prusa MK3S+ 3D printer. After assembling and setting the entire device up it looked as presented in (Fig.2).

Fig.2 - Complete laboratory stand
As it turned out the kitchen sponge is an excellent base for the sampless

Created device can serve as a form of cheap alternative to expensive, market-available devices when there is no necessity for resolution greater than 0.1N.

The presented device was created during the work carried out with my colleague G. Gruszka, Msc Eng, and others. These works, which I am involved in, have been accepted for publication as part of a scientific conference:

Driver for camera and equatorial telescope mount

Astrophotography, also known as astronomical imaging, is the photography of astronomical objects, celestial events, or areas of the night sky. Besides being able to record the details of extended objects such as the Moon, Sun, and planets, modern astrophotography has the ability to image objects invisible to the human eye such as dim stars, nebulae, and galaxies. This is accomplished through long time exposure as both film and digital cameras can accumulate and sum photons over long periods of time.

Weaker stars and deep-sky objects unfortunately have such low brightness that in order to capture them in a photograph, the shutter speed (exposure time) must be relatively long. While in typical daytime photography, exposure times of fractions of a second (1/800s or even shorter) are used, in astrophotography shutter speeds can range from tens of minutes to several hours.

When taking photographs of the night sky using long exposures, the rotation of the Earth around its axis causes an interresting effect (Fig.3).

Movement of stars on the celestial sphere (visible Orion constellation and others).

Long exposure photography can capture mesmerizing star trails, created by the apparent movement of stars in the night sky as the Earth rotates on its axis (Fig.4).

Fig.4 - Star trails

Telescope mounts and other equipment that compensate for the Earth's rotation are used for longer exposures without objects being blurred. They include commercial equatorial mounts and homemade devices. Mounts can suffer from inaccuracies due to backlash in the gears, wind, and imperfect balance, and so a technique called auto guiding is used as a closed feedback system to correct for these inaccuracies (Fig.5).

Fig.5 - My example setup for astrophotography: a small Maksutov telescope with a digital SLR camera and autoguider (both with lens heater) mounted on an equatorial mount.

In my works I use techniques that involve capturing multiple images (sometimes thousands) and compositing them together in an additive process known as stacking. This technique sharpens images, overcomes atmospheric distortions, compensates for tracking errors, enhances the visibility of faint objects with low signal-to-noise ratios, and filters out light pollution. In simple terms, instead of taking a single photograph with a very long exposure time, stacking involves taking multiple pictures with shorter exposures, which are then combined into a single photo with better parameters.

To facilitate the use of a digital SLR camera as a sensor in astrophotography, I have built a suitable device which I named AstroDriver (Fig.6).

Fig.6 - The AstroDriver
A - Remote trigger cable socket for digital SLR camera, B - Display (2x16 chars), C - External power supply socket,
D - Main power switch, E - Selection knob, F - Connector for external device

The main component of the device is the ATMEGA8 microcontroller, with an external 8MHz quartz crystal resonator. A certain problem arose when it was discovered that at low temperatures, the response time of the LCD display used significantly increased, and the contrast decreased. To enable the driver to operate for hours at temperatures below 0°C, a heating element was utilized to maintain the temperature of key components of the device at an appropriate level. The firmware was written in C and take up approximately 50% of the microcontroller's FLASH memory.

The AstroDriver is essentially a specialized intervalometer with additional features useful in astrophotography. Menu navigation is done with an encoder that has a built-in momentary switch. There are three main modes available:


In normal mode, the user can select the interval between photos in the range of 1s-99h (exposure usually limited to 30-120s, it's depends on type of SLR). Bulb mode allows setting both the interval and the camera's shutter speed in the same range of 1s-99h. In normal and bulb modes, you can enable the option to put the digital SLR in standby mode between photos to reduce power consumption (device will send to the camera signal for wake up before taking the next photo). I have also implemented the possibility of controlling external devices - there are two outputs with galvanic isolation (one normally on and one normally off) programmed independently. The set parameters are stored in non-volatile EEPROM memory.

Astro mode requires connecting the AstroDriver to both the digital camera and the control system of the equatorial mount. This enables me to automate the process of polar alignment, which involves aligning the rotational axis of a telescope's equatorial mount parallel to Earth's axis. This procedure is necessary so that the equatorial mount can effectively compensate for the effects of the Earth's rotation.

The AstroDriver enables easier taking of long-exposure photography, where stars remain sharp and no trails are observed (Fig.8, vide Fig.4).

Fig.8 - Stars with no trails

AstroDriver is very helpful in properly setting up an equatorial mount and taking photos. Figures 9-11 show example photographs of deep sky objects that I was able to capture using the described technique.

Fig.9 - The Horse Head Nebula

Fig.10 - The Pleiades

Fig.11 - The Orion Nebula

The device turned out to be so versatile that it also proved useful in other applications, such as time-lapse photography. Thanks to this, videos showing relatively slow processes were created, such as the formation of Liesegang rings (Vid.1) or the growth of silver crystals in silica gel (Vid.2).


I built AstroDriver in 2016 and since then there has been no malfunction even despite intensive use.

Low voltage Solid State Tesla Coil for use in education

A Tesla coil is an electrical resonant transformer circuit designed by Nikola Tesla in 1891. It is used to produce high-voltage, low-current, high-frequency alternating-current electricity. Tesla experimented with a number of different configurations consisting of two, or sometimes three, coupled resonant electric circuits.

Solid State Tesla Coil (SSTC) use power semiconductor devices, usually thyristors or transistors such as MOSFETs or IGBTs, triggered by a solid state oscillator circuit to switch pulses of voltage from a DC power supply through the primary winding.

I built a very simple device based on an electronic circuit called the Slayer Exciter. To construct it, only one transistor and a few other electronic components are needed. The most important part of the device is a system of two single-layer coils wound on an empty plastic tube (Fig.12).

Fig.12 - Primary and secondary coils

My miniature (fitting in the palm of the hand) Tesla coil powered by a 9V battery can be seen in Fig.12.

Fig.13 - Miniature SSTC

The electromagnetic field around device is so strong that it easily induces glow discharges in a mercury lamp (Fig. 14) and a fluorescent tube (Fig. 15).


Walking robot with AAM module

Studying the anatomy of insects has inspired me to develop walking robots. While exploring the applications of this field in technology and education, I conceived the idea of constructing a simple robot for educational purposes. The primary objective was to utilize readily available materials and tools, ensuring affordability in its construction while also providing an opportunity for anyone interested to gain knowledge about designing. This led to the creation of the MUTRA robot, which has the following features:

I based the mechanical design on my earlier educational robot REKSIO but with significant improvements.

Fig.16 - MUTRA

In order to facilitate the use of the robot in education and popular science lectures, I equipped it with an Audience Attraction Module (AAM) according to my own idea and construction. AAM is simply a remotely controlled flamethrower (Fig.17). The sight of a small robot producing a stream of fire on demand attracts the attention of even the most bored audiences and allows them to become interested in the topic being discussed.

Fig.16 - MUTRA in action

For safety, a mixture of propane and butane was used as fuel for the flamethrower. The ordinary balloon, on the other hand, serves as a gas reservoir. This has the advantage that the flammable gas is stored at a relatively low pressure - in case of an accident, the entire amount of gas can be burned in one second without causing significant danger. The gas outlet is moved vertically by a servo mechanism, and ignition is electrically activated.


Several levels of protection have been implemented to minimize the risk of accidents. However, I want to emphasize that MUTRA can only be used by me and other trained people.

Fig.17 - Berserk mode

The ionization chamber and 220Ra - a simple method for determining the half-life time of radionuclides

The ionization chamber is the simplest type of gaseous ionisation detector, and is widely used for the detection and measurement of many types of ionizing radiation, including X-rays, gamma rays, and beta or alpha particles.

The term ionization chamber refers exclusively to those detectors which collect all the charges created by direct ionization within the gas through the application of an electric field. It uses the discrete charges created by each interaction between the incident radiation and the gas to produce an output in the form of a small direct current. This means individual ionising events cannot be measured, so the energy of different types of radiation cannot be differentiated, but it gives a very good measurement of overall ionising effect.

Ionization chambers can be built in various ways. Their operating principle is so brilliantly simple that they can be constructed from cheap and easily available materials and used in research and education. In Fig.18, you can see the ionization chamber constructed by me from a metal can and copper wire. I used a simple DC amplifier, which allows to observe changes in the electric current on a multimeter - as we can see, current increases significantly when a sample of the radioactive isotope emitting alpha radiation (241Am) is close to the chamber.


Half-life t½ is the time required for a quantity of substance to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive.

To determine the half-life of a given radionuclide, we can use an ionization chamber. I have decided to choose the radon isotope 220Rn as the object of my study. Radon is a colorless, odorless, and tasteless noble gas and therefore is not detectable by human senses alone.

Radon has no stable isotopes. Thirty-nine radioactive isotopes have been characterized, with atomic masses ranging from 193 to 231. The most stable is 222Rn (t½ = 3.8 days), which is a decay product of 226Ra, a decay product of 238U. The 220Rn isotope is a natural decay product of the most stable thorium isotope 232Th, and is commonly referred to as thoron.

The mentioned radon isotope has many features that are particularly advantageous in the described experiment. One of them is the fact that the half-life of 220Rn is short enough (< 1 min) to be determined fairly accurately during relatively short measurements. During radioactive decay, it emits alpha particles that are easy to detect in the ion chamber. Obtaining radon for experimental purposes is not difficult because it accumulates naturally in vessels containing thorium or it's compounds.

The setup presented in Fig.19 was used to measure the half-life of 220Rn. The ionization chamber A is constructed from a metal can with a diameter of approximately 20 cm (7.9 in), and the second smaller can contains a DC amplifier with bias regulation B. This circuit allows the measurement of voltage (multimeter C) proportional to the current generated by ionization in the chamber caused by radon isotope injected into the chamber using a syringe D. The system is powered by a single 9V battery E.

Fig.19 - My setup
A - Ionization chamber; B - Bias regulation; C - Multimeter (cheap one); D - Syringe; E - 9V battery

Before starting the measurement, it is necessary to connect the power supply voltage and adjust the bias so the output voltage is 0V.

The actual measurement begins at the moment of injecting a certain volume of air containing 220Rn into the chamber. From that moment on, the output voltage should be measured at known time intervals. The voltage initially rises and then begins to decrease with the decay of the radionuclide.

The following graph (Fig.20) shows the data obtained during a single measurement using the described method.

Fig.20 - The decrease of the output voltage as a function of time
orange - actual data, blue - regression

The half-life of radon can be determined as the interval in which the radioactive activity represented by the measured voltage decreases by half, for example, from the value U1 to U2 (U2 = U1/2). In the described case, t½ = t2 - t1.

During a single measurement, the half-life time was determined as 56.2 s, while the exact value according to the data available in the literature is 55.6 s. As can be seen, even using such a simple and inexpensive equipment, it was possible to determine the value of the half-life time for 220Rn quite accurately.

The Voice of Energy - Plasmophone

Apart from projects with scientific value, I also work on ones that are created purely for the pleasure of creation or just for fun. My work on generating sound using thermal vibrations of plasma created in an electric arc falls into this category.

I conducted my first experiments on a plasma speaker that I constructed using the ZVS circuit. This device, equipped with an appropriate transformer, allows for the generation of high voltage (in my case, about 20kV). By modulating the output current, I achieved variations in the temperature and gas pressure of the electric arc, enabling produce sound and play melodies — in this case, the Cuckoo Waltz (see Video 4). The sound is very loud, causing severe distortion in the signal from mic.

Vid.4 - the Cuckoo Waltz on Plasmophone

In later experiments, I used a modern CRT television flyback transformer with an integral tripler and a TL494 chip. This allowed me to generate an electric arc that was almost 10 cm (3.9 in) long. The resulting sound is deafeningly loud in close proximity. In my opinion the writhing electric arc is truly hypnotizing (Vid.5).

Vid.5 - Ievan Polkka on Plasmophone

All sounds you can hear in the Vid.4 and Vid.5 are produced by the vibrating plasma of the electric arc.

I want to emphasize an important point: these types of experiments can be really dangerous to life, especially in the case of electric shock or thermal burns. Such work can only be carried out by specialists who have the necessary knowledge and experience.

Acoustic levitation

Acoustic levitation is a technique used to suspend matter in the air against gravity using acoustic radiation acoustic radiation pressure generated by high-intensity sound waves. Usually, ultrasonic frequencies are used, making the sound inaudible to humans due to the high intensity required to counteract gravity.

Various methods are available for generating the sound, with the most widespread approach involving the use of piezoelectric transducers capable of efficiently producing high-amplitude outputs at the desired frequencies.

In my research, levitated particles are trapped at the nodes of a standing wave (Fig.21c) created by a sound source (Fig.21a) and reflector (Fig.21b).

Fig.21 - Acoustic levitation,
my setup

This approach relies on the particles being significantly smaller than the wavelength, typically around 10% or less, and the maximum weight of the levitated particles is usually in the range of a few milligrams. It's important to note that if the particle size is too small relative to the wavelength, it will exhibit different behavior and move towards the anti-nodes. This levitation system is single-axis, meaning that all particles are trapped along a single central axis of the device (Vid.6).

Vid.6 - Levitation of small objects with sound

Simple hardware speech synthesizer

Speech synthesis refers to the creation of artificial human speech. To accomplish this, a computer system known as a speech synthesizer is used, which can be implemented either as software or hardware. A text-to-speech (TTS) system is one example that converts regular language text into speech. Alternatively, there are other systems that convert symbolic linguistic representations - such as phonetic transcriptions - into speech. However, specialized computer programs are commonly utilized for this purpose, because generating human-like synthetic voice requires significant computational power.

Computer-based speech synthesis began in the late 1950s. In 1968, Noriko Umeda developed the first text-to-speech system in Japan. In 1961, physicist John Larry Kelly, Jr. and Louis Gerstman used an IBM 704 computer at Bell Labs to synthesize speech, notably recreating the song "Daisy Bell". During a visit to Bell Labs, Arthur C. Clarke (science fiction writer, science writer, futurist, inventor and undersea explorer) witnessed the demonstration and later incorporated it into the climactic scene of his screenplay for his novel "2001: A Space Odyssey", where the fictional computer HAL9000 sings the same song before being shut down by Dave Bowman.

During my work in the field of robotics, it became apparent that a hardware-based real-time speech synthesis capability would be useful in that. There are various solutions available, such as utilizing Arduino with some libraries or integrated circuits like SpeakJet. While these options are indeed helpful, the majority of them generate speech in the English language, and there is a lack of devices that enable speech synthesis in Polish. Therefore, I decided to construct my own hardware synthesizer.

I used an ATMEGA8 microcontroller (16MHz) as the main active component of the device. Sound samples in the form of phonemes isolated from my own voice were stored in a serial EEPROM 256-Kbit memory AT24C256C. This chip is I2C compatible, making communication and data transmission between the processor and memory highly convenient.

At the initial stage of this work, it became clear to me that the task I undertook would not be easy. It became necessary to develop a custom phonetic-grammatical engine that would interpret the text and select phoneme sound samples from a database, which would then be played back in the correct order at an appropriate (sometimes variable for purpose of intonation) speed. The firmware I wrote filled nearly the entire available memory of the microcontroller, but it performs its task perfectly, transforming the text into understandable Polish speech (Vid.7).

Vid.7 - In action

My synthesizer allows for speech synthesis based on any text transmitted to the device via UART. The system autonomously interprets and adjusts the intonation, rhythm, and pace of speech based on punctuation marks such as periods, question or exclamation marks, and commas. There is also the possibility of including additional commands in the text to control the volume and speed of the generated speech.

Whiteboard Drawing Robot

This project was created for educational purposes, and I based it on resources available here.

The hardware platform is based on Arduino Uno, a motor driver (L293D chip), and two Nema 17 stepper motors. The control software for the device is Polargraph running on a computer. Communication between the laptop and the robot is established via USB.

The drawing element of the robot with a whiteboard marker, is moved on toothed belts driven by two Nema motors located in the upper corners of the board. The gondola is equipped with a servo mechanism, enabling the marker to be pressed against or lifted from the board. This allows the robot to draw virtually any single-colored graphic on the board by importing any *.SVG vector file into the application on the laptop (Vid.8).

Vid.8 - Robot drawing on whiteboard in action

Using the described technique, the robot can create even more detailed drawings. (Vid.9).

Vid.9 - Next drawing on my board

That's not all

For more information about these and other experiments or constructions, please visit You can also contact me by email (