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TOTEM: studying by experimenting – Open Electronics


Let’s find out about an attention-grabbing academic platform that permits you to make and examine an actual multitude of digital circuits and their functions.

Among the many methods to method college students and really younger folks, the one among utilizing ecosystems associated to prototyping boards reminiscent of Arduino has proved to be very efficient; subsequent to it and, we are able to say, in synergy with it, a collection 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 surroundings, since it’s based mostly on an Arduino-like board, Totem Mini Lab consists of a wide range of measurement instruments and digital blocks prepared to make use of for experiments.

Designed for use along side the Totem constructing system, it permits you to 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 broaden capabilities.

The usage of Totem Mini Lab is easy and engaging, additionally as a result of it would not be mandatory to fret about making wiring, usually messy, precarious connections, and so forth.. 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 required boards and that teams all the essential electronics of the laboratory.



The core of the electronics is a particular model of Arduino UNO known 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 parts and circuits in an effort to broaden the experimentation space when the weather on the body will not be 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 Pc.


Full with a richly illustrated technical handbook in English, explaining how one can get began and using Totem components to construct a workbench.



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


Fig. 1


This board incorporates quite a lot of 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 check unit.

The cardboard accommodates the next modules:

  • part suitable with Arduino Shields;

obtainable 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 alerts;

– ± 5V to measure alerts with TTL logic degree;

– ± 50 V for measuring exterior alerts;

  • 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 collection 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 permits you to join TotemDuino to the LabBoard, facilitating entry to the pins;
  • 5V voltage regulator to produce comparatively excessive energy masses;
  • microcontroller logic voltage selectable between 5 V and three.3 V.

The board is subsequently a board with an Arduino UNO core however outfitted with connections and {hardware} configuration optimized for the Totem surroundings. The structure of the board parts is proven in Fig. 2.


Fig. 2



One function of the Totem platform is that it’s based mostly on a body that teams the electronics, so experimentation turns into simple and doesn’t contain having the bench plagued by digital boards in disarray; all the things is organized on a three-dimensional body that makes it simple to see and join all the weather on board. This construction makes it simple to improve and broaden: simply add the mechanical or digital components required by the appliance.

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

The construction based mostly on the body is so compact that, if wanted, it’s doable to maneuver the circuit realized from the laboratory bench instantly on the sector, for instance, to check in apply a simulated software; multi function physique, with out having to get assist to maneuver and to help boards, wires and every other “flying” components.

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


Fig. 3



The Totem MiniLab system features a collection of optionally available aspect panels that include separate, ready-to-use digital modules reminiscent of shows, sensors, switches and the rest 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 connected to the body and prepared for interconnection. The Aspect Panels include parts and modules which can be usually used when testing an embedded challenge.

This lets you remedy 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 challenge, is connecting sure digital parts to the Arduino as a result of generally it’s troublesome to do and may trigger connection errors and generally harm from them since many parts don’t match properly on a breadboard and have to be linked flying. The fantastic thing about Totem is that it already has many parts on board (Fig. 5) to be interconnected for the conclusion of experiments and that its construction simplifies the addition of exterior components.


Fig. 5


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

The opposite aspect panels have enter units reminiscent of potentiometers and switches, relay drivers and DC motor drivers. There are additionally LED drivers and an OLED show to be used in additional advanced designs when values and indications should be displayed.


Fig. 6



After having launched the Totem MiniLab platform, to provide you an concept of what you are able to do with it, we suggest the conclusion 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 based mostly 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 obtainable amplitude.

Observe which you can hearken to the sign by inserting a jumper on the contacts (headers) labelled “SP ON” that’s positioned simply above the speaker on the proper.


Fig. 7



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

Fig. 8


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

For this goal, on the output of the filter, we join a small circuit known 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 detrimental half-waves) ensures that the sign downstream of the circuit, i.e. at its ends, is all optimistic (above zero volts). The height detector circuit returns on the cathode of the second Schottky (the one in collection 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 part proportional to the amplitude of the sine wave sign popping out of the high-pass filter (Fig. 9). Figuring out the amplitude of the enter sign we are able to 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 it is a second-order filter). The cut-off frequency of our filter is given by the method:

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 needs to be famous, nonetheless, that it may differ relying on the tolerance of the parts, as we are going to 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 routinely performs the cut-off frequency measurement check within the full circuit carried out 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 obtainable on the aspect panel, reminiscent of 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 an information 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 simple it’s to make use of the completely different modules within the Aspect Panels, and many of the code offers with the frequency sweep, measurements, and outcome show.

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


// Fundamental MD_AD9833 check file
// Initialises the machine to default circumstances
#embrace <SPI.h>
#embrace <Wire.h>
#embrace <MD_AD9833.h>
#embrace <Adafruit_GFX.h>
#embrace <Adafruit_SSD1306.h>
//Outline display measurement in pixel
#outline SCREEN_WIDTH 128 // OLED show width
#outline SCREEN_HEIGHT 64 // OLED show peak
// 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 Knowledge 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),
show.peak(), 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
//calculate restrict freq



The experiment we simply performed reveals that with easy strategies, Arduino or not less than 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 indication of how measurements could be made, acquiring numerical and even graphical outcomes, because of the flexibility to make use of the small OLED show as knowledge output. The train generally is a foundation to broaden, for instance by sending the outcomes to a PC for a greater display to point out the graphs.



A platform of experiments

Minilab sensor enlargement

Audio Growth for Minilab

I/O Growth for Minilab




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