TOTEM: studying by experimenting – Open Electronics




Let’s find out about an attention-grabbing instructional platform that means that you can make and research an actual multitude of digital circuits and their functions.

Among the many strategies to strategy college students and really younger folks, the one in all utilizing ecosystems associated to prototyping boards corresponding to Arduino has proved to be very efficient; subsequent to it and, we will say, in synergy with it, a sequence of mini-labs and experiment kits have developed. Amongst these, it appears attention-grabbing to level out Totem Mini Lab, which is a small however highly effective transportable and benchtop electronics lab to experiment and study the fundamentals of electronics.

Absolutely suitable with the Arduino programming setting, since it’s primarily based on an Arduino-like board, Totem Mini Lab consists of quite a lot of measurement instruments and digital blocks prepared to make use of for experiments.

Designed for use together with the Totem constructing system, it means that you can construct compact workbenches with built-in breadboards, saving you from flying connections. Additionally it is suitable with I/O, sensor and audio enlargement boards, which might additional increase capabilities.

Using Totem Mini Lab is straightforward and enticing, additionally as a result of it’ll now not be crucial to fret about making wiring, usually messy, precarious connections, and so on.. for instance when with jumpers you wire the assorted breakout boards with Arduino: right here we’re confronted with a body that homes, already interconnected, the mandatory boards and that teams all the fundamental electronics of the laboratory.



The core of the electronics is a particular model of Arduino UNO referred to as TotemDuino and specifically developed. Let’s see what components make up the Totem experiment equipment, ranging from what’s within the field:

  • TotemDuino;
  • LabBoard, which is an experimentation and measurement platform;
  • 34-pin flat-cable to interconnect TotemDuino and LabBoard;
  • body to be assembled for the development of Totem workbenches;
  • mains energy provide (220 Vac / 12 Vdc 1.5 A) to energy your laboratory;
  • 2 breadboards with 700 contacts to attach exterior elements and circuits with a view to increase the experimentation space when the weather on the body aren’t sufficient;
  • 40 male-male jumpers about 20 cm lengthy + Set of 140 jumper cables for making connections on the experimental bases;
  • 1-meter lengthy USB-mini USB 2.0 cable to attach TotemDuino to the Private Laptop.


Full with a richly illustrated technical guide in English, explaining how you can get began and using Totem elements to construct a workbench.



Let’s now spend a number of strains going deeper into the principle board of Totem MiniLab, proven in Fig. 1.


Fig. 1


This board incorporates numerous peripherals and interfaces and may have a dual-use.

It may be used each as an enlargement board for the TotemDuino system (because it gives simply accessible enter and output connections) and as a measurement and take a look at unit.

The cardboard comprises the next modules:

  • part suitable with Arduino Shields;

out there output voltages:

  • 12 V/1 A – direct provide voltage
  • 5 V/0,5 A – regulated provide voltage, shared with TotemDuino.
  • 3,3V/0,25 A – regulated provide voltage, shared with TotemDuino and LabBoard processor;
  • -5V/0,5A – Separate regulated voltage, for experimentation with amplifiers;
  • programmable voltage output from 0 to three.3 V, as much as 0.35A;
  • digital/analog converter;
  • voltage measurement:

– ± 0.5 V for use when measuring small amplitude indicators;

– ± 5V to measure indicators with TTL logic stage;

– ± 50 V for measuring exterior indicators;

  • present measurement as much as 800 mA;
  • frequency meter with sign measurement functionality as much as 1 MHz;
  • pulse counter as much as 999.999.999;
  • arbitrary pulse generator, able to producing a sequence of pulses with programmable width and interval.



Absolutely suitable with Arduino UNO, the board that’s the mind of the TotemDuino platform has the next functionalities:

  • I / O safety; all of the output pins that enter the LabBoard are protected in opposition to overvoltage or quick circuits;
  • 34-pin enlargement connector for flat cable that means that you can join TotemDuino to the LabBoard, facilitating entry to the pins;
  • 5V voltage regulator to provide comparatively excessive energy masses;
  • microcontroller logic voltage selectable between 5 V and three.3 V.

The board is due to this fact a board with an Arduino UNO core however outfitted with connections and {hardware} configuration optimized for the Totem setting. The format of the board elements is proven in Fig. 2.


Fig. 2



One characteristic of the Totem platform is that it’s primarily based on a body that teams the electronics, so experimentation turns into straightforward and doesn’t contain having the bench suffering from digital boards in disarray; every little thing is organized on a three-dimensional body that makes it straightforward to see and join all the weather on board. This construction makes it straightforward to improve and increase: simply add the mechanical or digital elements required by the appliance.

It additionally consists of all of the mechanical components wanted to assemble the body.

The construction primarily based on the body is so compact that, if wanted, it’s doable to maneuver the circuit realized from the laboratory bench immediately on the sphere, for instance, to check in follow a simulated software; multi functional physique, with out having to get assist to maneuver and to assist boards, wires and some other “flying” components.

This attribute of the Totem system, which you’ll uncover by utilizing it, is especially considerable and makes a distinction with competing options.


Fig. 3



The Totem MiniLab system features a sequence of optionally available facet panels that include separate, ready-to-use digital modules corresponding to shows, sensors, switches and anything that will should be added to carry out explicit experiments.

Fig. 4 reveals the MiniLab Totem outfitted with what they name “Aspect Panels” and a breakout board hooked up to the body and prepared for interconnection. The Aspect Panels include elements and modules which are usually used when testing an embedded undertaking.

This lets you clear up many issues typical of experimental circuits that require many components.


Fig. 4


One other downside when constructing prototypes, or simply wanting to check a code for a undertaking, is connecting sure digital elements to the Arduino as a result of generally it’s troublesome to do and may trigger connection errors and generally injury from them since many elements don’t match nicely on a breadboard and have to be linked flying. The fantastic thing about Totem is that it already has many elements on board (Fig. 5) to be interconnected for the belief of experiments and that its construction simplifies the addition of exterior components.


Fig. 5


The Aspect Panels have blocks that accomplish a number of steadily used capabilities: there are audio circuits, perform turbines, and BF amplifiers with audio system.

The opposite facet panels have enter gadgets corresponding to potentiometers and switches, relay drivers and DC motor drivers. There are additionally LED drivers and an OLED show to be used in additional complicated designs when values and indications should be displayed.


Fig. 6



After having launched the Totem MiniLab platform, to present you an thought of what you are able to do with it, we suggest the belief of an train that higher than any phrases exposes and explains the potential of the system: we’re going to use the on-board perform generator primarily based on the built-in AD9833, which lets you generate sine, triangle and sq./rectangular waveforms.

The frequency generator is managed by the Arduino board by way of three I/O pins, which is the SPI interface within the ARDUINO (Serial Programming Interface) code. We’ll use the included audio amplifier to get extra amplitude from the frequency generator and we’ll set the quantity pot to most, once more to maximise the out there amplitude.

Be aware you could take heed to the sign by inserting a jumper on the contacts (headers) labelled “SP ON” that’s situated simply above the speaker on the fitting.


Fig. 7



The experiment we’ll present right here will use the perform generator to supply a sinusoidal sign that shall be despatched to a easy high-pass LC filter. Since we shall be measuring standing waves solely, it’s not essential to match the output impedance of the generator and the enter impedance of the filter; it is not going to be, as a substitute, doable to make use of such a filter for transient indicators, however right here it’s not an issue as a result of we’re merely fascinated about discovering the cutoff frequency. Fig. 8 reveals the schematic of the filter and the placement of its elements on the corresponding Aspect Panel.

Fig. 8


When measuring sinusoidal waveforms, one of the best factor to do is to rectify the waveform and create a unidirectional, quasi-continuous voltage, which the Arduino ADC can precisely measure.

For this function, on the output of the filter, we join a small circuit referred to as a peak detector, along with a blocking diode. The blocking diode (it’s a Schottky linked in such a means as to chop off the unfavourable half-waves) ensures that the sign downstream of the circuit, i.e. at its ends, is all constructive (above zero volts). The height detector circuit returns on the cathode of the second Schottky (the one in sequence with the capacitor) a no-load voltage that ideally is the same as the height voltage of the sine wave (in actuality it is the same as the height minus the minimal direct drop on the Schottky diode), which permits acquiring a steady element proportional to the amplitude of the sine wave sign popping out of the high-pass filter (Fig. 9). Realizing the amplitude of the enter sign we will deduce the cut-off frequency as a result of it’s the one at which the ratio between the output voltage and the enter voltage is 0.5 or -6dB (do not forget that this can be a second-order filter). The cut-off frequency of our filter is given by the formulation:

fc= 1 / (2*π*√LC )


and the values predicted by the experiment, proven within the electrical diagram of the filter in Fig. 8 are theoretically 340 Hz. It must be famous, nevertheless, that it could differ relying on the tolerance of the elements, as we’ll see by analyzing the outcomes of the experiment performed.


Fig. 9



So let’s take a look at the firmware to be loaded into Arduino, which mechanically performs the cut-off frequency measurement take a look at within the full circuit applied on the platform as proven in Fig. 10. To carry out the duty, the sketch makes use of some libraries for the capabilities of the electronics out there on the facet panel, corresponding to SPI.h for 3-wire serial communication with the AD9833 frequency generator and Wire.h for I²C serial communication. The firmware additionally consists of the MD_AD9833.h library for managing the AD9833 perform generator chip and gives for the administration of the 128×64 pixel OLED show utilizing the Adafruit particular libraries: Adafruit_SSD1306.h and Adafruit_GFX.h for drawing and writing to the show.


Fig. 10


In our design, the outcomes of the frequency scan after which sweep are displayed on an OLED show on Aspect Panel 2 within the type of a frequency response curve (Fig. 11). Every measurement is saved in a knowledge array and plotted as a pixel on the show. Then the cutoff frequency is calculated and written down. The show is managed by the Arduino by way of the I²C bus. The TotemDuino makes use of the Wire.h library for communication over the I²C bus by way of the A4 (SDA) and A5 (SCL) I/O pins.


Fig. 11


The code, proven in full within the screenshots how straightforward it’s to make use of the totally different modules within the Aspect Panels, and many of the code offers with the frequency sweep, measurements, and consequence show.

The sweep is used to ship a large sufficient frequency spectrum to the enter of the filter that the amplitude development can then be checked on the output, i.e. on the filter capacitor beneath take a look at.


// Primary MD_AD9833 take a look at file
// Initialises the system to default circumstances
#embody <SPI.h>
#embody <Wire.h>
#embody <MD_AD9833.h>
#embody <Adafruit_GFX.h>
#embody <Adafruit_SSD1306.h>
//Outline display screen measurement in pixel
#outline SCREEN_WIDTH 128 // OLED show width
#outline SCREEN_HEIGHT 64 // OLED show top
// Declaration for an SSD1306 show
#outline OLED_RESET -1
// Reset pin # (or -1 if sharing Arduino reset pin)
//Initialize show
Adafruit_SSD1306 show (SCREEN_WIDTH,
// Pins for SPI comm with the AD9833 IC
#outline DATA 11 ///< SPI Information pin quantity
#outline CLK 13 ///< SPI Clock pin quantity
#outline FSYNC 10 ///< SPI Load pin quantity
#outline SAMPLES 64
MD_AD9833 AD(FSYNC); // {Hardware} SPI
int freq;
int buffer[SAMPLES];
void setup(void)
show.start(SSD1306_SWITCHCAPVCC, 0x3C);;
freq = 100;
void graphSpectrum(void)
int i;
int worth = buffer[i] / 4;
show.drawLine(i*2, 63-value, (i*2)+1,
63-value, SSD1306_WHITE);
int minfreq;
int maxfreq;
int stepF;
void frequencySweep(int minf, int maxf, int steps)
minfreq = minf;
maxfreq = maxf;
stepF = (maxf - minf) / steps;
int f = minf;
for(int i=0;i<steps;i++){
AD.setFrequency(MD_AD9833::CHAN_0, f);
f += stepF;
buffer[i] = analogRead(A0)/4;
void calculateFreq()
//seek for min and max
int minv=255,maxv=0;
int mini=0,maxi=0;
for(int i=0;i<SAMPLES;i++)
minv = buffer[i];
mini = i;
maxv = buffer[i];
maxi = i;
int f = 0;
for(int i=0;i<SAMPLES;i++)
//discover the worth that goes -3dB from max:
if(buffer[i]> (maxv/2))
f = i;
//Print on serial
Serial.print(“ “);
Serial.print(“ “);
//Print on show
show.drawLine(f*2, 0, (f*2),, SSD1306_WHITE);
char message[16];
sprintf(message,”fc:%d Hz”, minfreq + (stepF*f));
show.setCursor(0, 0);
//loop routine
void loop(void)
//accumulate samples
frequencySweep(20, 1000, SAMPLES);
//replace display screen
//calculate restrict freq



The experiment we simply performed reveals that with easy strategies, Arduino or at the very least an Arduino-like board just like the TotemDuino can be utilized for automated measurements in important electrical and digital circuits.

The LC filter we used on this setup was an illustration of how measurements might be made, acquiring numerical and even graphical outcomes, due to the power to make use of the small OLED show as knowledge output. The train could be a foundation to increase, for instance by sending the outcomes to a PC for a greater display screen to point out the graphs.



A platform of experiments

Minilab sensor enlargement

Audio Enlargement for Minilab

I/O Enlargement for Minilab




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