Saturday, March 21, 2020

Teaching Electronics to Kids

My "Introduction to Practical Electronics for Children" course concluded successfully a few weeks back, before March break. Now, with schools closed for covid19, it would be a good time for the kids to practice soldering and learn by doing. At this stage, I think it is easy to expand their knowledge and skills in the field of electronics just by assembling kits.

Here are a few notes and observations from my teaching.
  • Each class had 6 groups of 3 students sharing a soldering station. This (not my decision) was probably based of space constraints (6 desks in a normal-sized classroom) and safety/supervision considerations. It worked pretty well: the 2 students (in each group) not soldering had time to observe, analyze, think and to ask lots of questions. Two professional teachers assisted, with supervision, helping the students and keeping discipline.
  • Each student had their own "HDSP clock" kit to assemble. It took 6 one-hour sessions to complete, with a success rate of about 95% (2 failures out of 38 assembled, because of solder bridges).
  • The intended "50% theory and 50% practice" ratio had quickly become 10/90. Still managed to introduce components (resistor, capacitor, crystal), electrical concepts (AC vs DC, voltage, resistance, current, frequency) and units of measures (Volts, Farads, Ohms, Hertz). We even talked about Tesla batteries :)
  • Some parts were lost (e.g. crystal) or damaged (dropped, then stepped on by accident) between or during the classes. The lesson learned is to have extras available.
  • Each student received individual instructions, guidance, assistance and supervision on soldering. We came up with the "3-second rule" to make a good soldering joint: hold the tip of the soldering iron in contact with the pad and the terminal for 3 seconds while touching and melting the solder wire on the tip.
  • Having students pay attention to the instructions was very important. It saves energy to talk once to the whole class, rather than answering the same question to each individual. (I also learned from professional teachers  the "1-2-3 eyes on me" attention-getter.)
  • Sockets for integrated circuits are a must in a beginner kit. Imagine fixing an IC soldered in the wrong orientation! (The "worst" that happened was that all 3 ICs in the kit were soldered directly onto the board, luckily in the correct orientation.) Also, silkscreen should be as detailed as possible, indicating the component's place. In case of the "HDSP clock" kit, the students were able to easily identify the placeholders for each component, just by using logic (except for the resistors; they learned quickly to bend the resistors' terminals).
  • Some of the most frequent mistakes were soldering bridges and filling empty holes with solder. Bridges were easily fixed (initially by me, then the students learned to do it themselves) using the copper wick/braid, and flux. To fix the solder-filled holes, I had to use a tailor pin (part of my EDC Swiss card).
  • Surprisingly, every student showed interest in working on, and completing, the kit. I think it was a successful experiment even for the school, in making "practical electronics" as part of their curriculum. Like in the old days of practical skills teaching (wood working for boys, sewing or cooking for girls), this course demonstrated that Grade 6 students are very capable and eager to acquire skills that may stay with them for life.

Sunday, March 15, 2020

Teardown of an Old Dimmer Switch

The 40+ year-old dimmer (made by Nortron Industries Limited in Milton, Ontario) in my attic broke down. Electronically, the dimming circuit still worked, but mechanically, the push button got stuck.
This is what's inside, for the curious.



The active component in the circuit is Q2006LT, a "quadrac" which, according to the datasheet, "is an internally triggered Triac designed for AC switching and phase control applications. It is a Triac and DIAC in a single package, which saves user expense by eliminating the need for separate Triac and DIAC components".

The "reversed-engineered" schematic looks like this:


For those who want to understand more on how the triac-controlled dimmer works, this article provides an in-depth explanation.

The 250V capacitors may be reused in a Nixie high-voltage (~170V) power source. For a hoarder, both the choke and the potentiometer (push button removed) look good.

I will report back on the internals of the replacement switch in 40 years or so, when it breaks down. I hope I/it last(s) that long.

Wednesday, March 11, 2020

Rothko Clock Nixie Shield with 6 IN-17 tubes

This compact 6-tube Nixie shield was designed by Tyler a long time ago, when kickstarter was young, and I was following closely and contributing often. Soon after the successful campaign, this open source project, together with its supporting documentation and web site, seemed to have disappeared from the internet.
I already reviewed the Nixie shield here (as part of the "Rothko" clock), and covered it a bit more in another post.
Since I found it appealing, both as a soldering kit and as a miniature Nixie board, I also:
  • modified slightly the original schematic (eliminated the under-the-tube LEDs)
  • redesigned the PCB
  • named the clock "Rothko", to accompany my other clocks in the masters series, "Mondrian" and "Kandinsky". Note that, in this case, the "Rothko" clock is the union of 2 boards: this 6-tube Nixie shield and wsduino (which itself can be replaced by any Arduino with an RTC).


A kit for the Nixie shield is offered on Tindie. The PCB was designed to be self explanatory, but some people prefer the safety of assembly instructions. The slides below, recycled from the original deck, show the sequence of steps.


Once fully assembled, plug the Nixie shield into your Arduino, then upload this basic clock sketch (reads RTC and displays hours and seconds; no setting buttons, no Bluetooth, no buzzer/alarm):

#include "Arduino.h"
#include "avr/pgmspace.h"
#include "Wire.h"
#include "DS1307.h"
#include "avr/io.h"
#include "avr/interrupt.h"

// global variables
unsigned char INDEX = 1;   /* 1 to 6 */
unsigned char HOUR  = 7;   /* 1 to 12 */
unsigned char MINUTE = 45;  /* 0 to 59 */
unsigned char SECOND = 23;  /* 0 to 59 */

boolean is12HMode = false;


// read time from DS1307 at intervals;

#define MAX_TIME_READING_COUNTER  15000
long timeReadingCounter = MAX_TIME_READING_COUNTER;


// timer2 used for nixie tube multiplexing

ISR(TIMER2_COMPA_vect)
{
/* HOUR = 10, 11, or 12 or top of minute?*/
if ((HOUR / 10) || SECOND==0)
{
PORTB = 0x10;  // turn HOUR tens LED on
}
else
{
PORTB = 0x00;  // turn HOUR tens LED off
}

switch(INDEX++)

{
/* HOUR tens place */
case 1:
/* blank anodes */
PORTD = 0x00;

/* set cathode */

PORTB |= (HOUR / 10);

/* only turn anode on if one */

if (HOUR / 10)
{
PORTD = 0x04;    
}
break;

/* HOUR ones place */

case 2:
/* blank anodes */
PORTD = 0x00;

/* set cathode */

PORTB |= (HOUR % 10);

/* turn on anode */

PORTD = 0x08;
break;

/* MINUTE tens place */

case 3:
/* blank anodes */
PORTD = 0x00;

/* set cathode */

PORTB |= (MINUTE / 10);

/* turn on anode */

PORTD = 0x10;
break;

/* MINUTE ones place */

case 4:
/* blank anodes */
PORTD = 0x00;

/* set cathode */

PORTB |= (MINUTE % 10);

/* turn on anode */

PORTD = 0x20;
break;

/* SECOND tens place */

case 5:
/* blank anodes */
PORTD = 0x00;

/* set cathode */

PORTB |= (SECOND / 10);

/* turn on anode */

PORTD = 0x40;
break;

/* SECOND ones place */

case 6:
/* blank anodes */
PORTD = 0x00;

/* set cathode */

PORTB |= (SECOND % 10);

/* turn on anode */

PORTD = 0x80;

/* reset index */

INDEX = 1;
break;
}
}

void setup()
{
// configure pins
pinMode(2, OUTPUT);
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);
pinMode(5, OUTPUT);
pinMode(6, OUTPUT);
pinMode(7, OUTPUT);
pinMode(8, OUTPUT);
pinMode(9, OUTPUT);
pinMode(10, OUTPUT);
pinMode(11, OUTPUT);
pinMode(12, OUTPUT);

cli();  // disable global interrupts


// timer2 1kHz interrupt

TCCR2A = 0x00;
TCCR2B = 0x00;
TCNT2 = 0x00;
OCR2A = 0xF9;
TCCR2A |= (1 << WGM21);
TCCR2B |= (1 << CS22);
TIMSK2 |= (1 << OCIE2A);

sei(); // enable global interrupts

}

void loop()
{
    timeReadingCounter++;
    if (timeReadingCounter > MAX_TIME_READING_COUNTER)
    {
      getTimeFromRTC();
      timeReadingCounter = 0;
    }
}

void getTimeFromRTC()
{
int16_t rtc[7];

RTC_DS1307.get(rtc, true);


SECOND = rtc[0];

MINUTE = rtc[1];
HOUR = rtc[2];
if (is12HMode && HOUR > 12)
HOUR = HOUR - 12;
}

void setTime(int hour, int minute, int second)
{
  RTC_DS1307.stop();
  RTC_DS1307.set(DS1307_SEC, second);
  RTC_DS1307.set(DS1307_MIN, minute);
  RTC_DS1307.set(DS1307_HR, hour);
  RTC_DS1307.start();
}



Sunday, February 2, 2020

Introduction to practical electronics for children

I designed this 7-hour (one hour/day) course for 6 graders, as part of their STEM curriculum.
The goal is to introduce the children to practical electronics and teach them about:

1. electronic parts/components: how to identify/recognize them, how to measure (using a multi-meter), what they are used for (role in an electronic circuit):
  • resistors (current reduction), variable resistor/potentiometer, trimmer
  • capacitors (energy accumulator), variable capacitor
  • transistors (amplification)
  • coils (inductors)
  • diodes, LEDs
  • speakers. microphones
  • buttons, switches
  • integrated circuits, processors
  • displays
  • sensors (light, magnetic, proximity/infrared/ultrasound)
  • servo motors
  • relays
2. how to solder (using a soldering station), how to place and position parts on a board, how to check connection, how to follow steps of an instruction manual;

3. electricity and electronics concept:
  • voltage, current, resistance;
  • AC vs DC
  • digital vs analog
  • oscillation
  • rectification
  • amplification
  • series, parallel
  • voltage transformation (AC)
  • voltage regulation (AC, DC)
4. basic understanding/reading of schematics (wiring, electrical connections).


Required materials
  • soldering station + solder wire + de-soldering wick/braid + flux pen;
  • one kit (per student), with through-hole components to assemble and solder;
  • prototyping boards for soldering practice + LEDs + resistors + wires + batteries;
  • tools: wire cutter, pliers, screwdriver, tweezers, magnifier, multi-meter;
  • optional: panavise/third hand, power supplies, wires, connectors;

Course schedule

Day 1
theory: introduction to components; presentation and identification (1/2 hour)
practice: beginning soldering (1/2 hour) LED + resistor, using flux, soldering wire, wick, on prototype PCBs;

Day 2
theory: introduction of a simple clock kit or another, more familiar to me, simple HDSP clock kit; assembly analysis, component placement and positioning;
practice: solder passive components on PCB; assemble the HDSP clock;

Day 3
theory: more on components; introduction to schematics;
practice: solder the active components of the clock kit;

Day 4
theory: electricity concepts (digital vs analog);
practice: finishing up the kit assembly; power, test, use;

Day 5
theory: electricity concepts (voltage, current, resistance); example of other kits;
practice: learn to use an ohm/volt/meter;

Day 6
theory: electronics concepts (oscillation, rectification, amplification, sound generation etc.);
practice: bring an electronic toy, working or not; disassembly, analysis, repair (if needed);

Day 7
practice: continuation from Day 6; identification of components used in the toy; understanding of how it works; modding/expanding functionality/adding LEDs, speaker, buttons etc.;


We are already on "Day 3", but behind schedule. Soldering is harder for the kids than I originally thought. One thing that I overlooked was that each student needs individual attention/supervision on the practical side (soldering, component placement etc.). Half hour per day of hands-on practice is definitely too short at this level. The schedule may be a little aggressive for the average Grade 6, probably better suited for older and more disciplined students. In any case, I am working on adjusting the content of the course and the feedback I receive is amazing. Kids really enjoy the fact that it is practical and some of them are amazed when they see the LEDs they soldered actually lighting up.