Category Archives: Electronics

Electronics, Experimental

DIY ENEGIZER

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#128 making a simple energizer

Since I’ve been living in a rural area for the past few years I’ve had to come up with some affordable solutions to problems unique to my situation. One of these problems is keeping animals out of certain areas with methods that wont cause permanent harm but will definitely be effective. So the logical solution was to use electricity in the form of electro shocks. I searched for commercial solutions and found a few but they were a bit overkill/overpriced and of course not very hacker friendly… so I decided to make my own which I can always scale up with microcontrollers/relays/monitoring and all those nice to have features but for this one I wanted it to be plain old dumb without any programming required.

So I did my research and came up with a suitable schematic found the correct parts and settled on the good old 555 timer. Designed a very small PCB and got it manufactured a voila the idea became a reality and after a few tests it works perfectly fine.

Now the shock is created by the collapsing fields of the ignition coil I used for the project. I got the most basic simple coil that is driven by a suitable N-FET at a frequency and strength that I can fine adjust via a potentiometer on the PCB. The whole system runs on a 12V battery and consumes very little current.

I took inspiration for this device and modified and created my own flavour. Like everything in life no one can do everything by themselves so I would like to credit the source which got me started here.

With that being said I had a lot of fun making this device and it’s been working well I was also able to adjust the voltage to a very humane jolt so smaller animals know not to enter the area but also don’t get fatally hurt.

Electronics, Experimental

CUSTOM UPDI PCB

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#124 Making a Custom Programmer

Fake CH340N IC on the left real on the right

While looking for a good example PCB project I decided upon a simple UPDI programmer PCB for the well known new ATtiny ICs.
I had a few prerequisites I wanted to satisfy for the project.

  • Design must work but also have room for improvement
  • small SMD PCB design
  • BOM list and prices
  • simple schematic using KiCad
  • 1206 component size sop-8 IC size
  • USB-C
  • 2 sided PCB
  • all standard sizes for PCB manufacture
  • PCB panel example
Front
Back

I wanted the project to cover many of the basic and intermediate PCB manufacturing practices of course the IC is not very sophisticated and there is no impedance matching or equal length traces etc. However it shows how designing, quick and affordable manufacturing can be achieved in South Africa. Designing for manufacturing, thinking of the capabilities of the manufacturer and keeping best practices in mind at least to the best of my knowledge at that specific time.

In the project I keep things as standard as I can using metric measurements and easy milling panel design for the panel (no fancy curved edges or designs) although many interesting looking designs can be made surprisingly simple, it takes experience plus CAD artistic intuition. That being said I wanted this to be a simple and practical example I could use for teaching references later.

Getting to the component choices for a small UPDI programmer I chose the CH340N IC. It needs very little external components and has an internal crystal. Small and lightweight and perfect for my UPDI project. It is missing other pins like the reset pin but in my case this was not an issue. Always double check your IC datasheets and capabilities.

KiCad modal front
KiCad modal back

On that note I did receive some FAKE CH340N ICs and I tested them. They only worked on lower baud rates and adding LED indicator resistors to the TX and RX made them unstable. Unfortunately in this day and age fake ICs are very common you need to recognize them and weigh the balance between using them or not. Sometimes there’s a “good fake” so as a maker I may use this test projects or make throwaway projects but the characteristics of the IC are now different so any calculations are incorrect… so it’s a balancing act that no-one can escape. For production always use IC’s from the original manufacturer the stores are easily found online and it’s worth it in the end.

Simple schematic

All other components are very basic 1206 (easy to solder) SMD capacitors, resistors, TX/RX LEDs, power indication led, a diode 16-pin USB-c connector with 5k1 sense resistors keep the PCB copper balanced on both sides also saves etching chemicals for the manufacturer I also added some example fiducials and the copper stops 1mm from the edge of the PCB creating a small protection layer all around.

Since there is a USB-C connector I chose not to include any ESD or fuse but I would add these components to a commercial variant.

Also this v1.0 has the TX/RX LEDs on the wrong indication pins. I would change them to the USB side instead.

Overall I think it’s a good introductory example showing a simple design including some errors and fixes.

Panel front
Panel back
KiCad panel back
UPDI_programmerDownload

Electronics, Experimental

IO EXPANDERS

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#123 Looking at some common IO expanders

What to do when you are using n 8-pin MCU to to the job of a 16pin ore even a 20pin MCU? Well it depends.. but if all you are doing is using IO’s to switch for example relays or similar tasks where the amount of IO’s is important, and not the capabilities of the IOs then you may be able so save costs by purchasing an IO expander instead of an abundantly pin gifted MCU.

These come in all shapes and package sizes and don’t increase the project size too much. Also I tend to use I2C much more then SPI but IO expanders can support both these packages.

Examples like the PCF8574, MCP23017, 74LVC595 and the MCP23S17 which uses SPI if you want to use that instead. The expanders support interrupts but always double check the datasheet before purchasing!

Something similar but not an expander more of a multiplexer IC is the MC14051B Analog Multiplexer/Demultiplexer this is quite common and affordable at least in South Africa and allows analogue pins to be expanded instead of digital.

Some Links to shops in South Africa that sell these expanders:

PCF8574

MCP23017

74LVC595

  • not common in South Africa

MCP23S17

Arduino, Electronics, Programming

328P PORT MANIPULATION

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#122 ATMEGA 328P Port Manipulation

Pinout of the 328P
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/*
//
Pinout of the 328P:
                            __  __
   1              (RESET) |1  \/28| [D19][A5] PC5 (SDA)
   2       (RX) PD0  [D0] |2    27| [D18][A4] PC4 (SDA)
   3       (TX) PD1  [D1] |3    26| [D17][A3] PC3
   4            PD2  [D2] |4    25| [D16][A2] PC2
   5            PD3 [~D3] |5    24| [D15][A1] PC1
   6            PD4  [D4] |6    23| [D14][A0] PC0
   7                  VCC |7    22| GND
   8                  GND |8    21| AREF
   9           (XTAL) PB6 |9    20| VCC
   10          (XTAL) PB7 |10   19| [D13] PB5
   11           PD5 [~D5] |11   18| [D12] PB4
   12           PD6 [~D6] |12   17| [D11~] PB3
   13           PD7  [D7] |13   16| [D10~] PB2
   14           PB0  [D8] |14   15| [D9~] PB1
                           -------
*/

Port manipulation was not important to me when I started working with microcontrollers, in fact I didn’t even know it existed and never felt the need for it especially after programming mostly in java script and PHP using functions like digitalread(pin); or digitalwrite(pin); etc. was second nature and speed or efficiency considerations were not really necessary or thought about that much.

Then after intermittently playing around with embedded ICs I got serious during the corruption virus of 2019 during lockdowns and other dilemmas while a lot of corrupt and diabolical cronies enriched themselves. I had a lot of time to focus on a few different things. There was no way I was going to let the circumstances get to me I made sure I was achieving at least one big goal each year and not get bogged down.

I took a look at the IC market and even though there was a chip shortage there were some IC’s available. This mad me try and get into efficient code and cost per IC. I came to the conclusion that I could get hold of IC’s with low memory + flash and very affordable prices. However in order to use them I would have to learn to use port manipulation, macros and interrupts in very efficient ways to the best of my ability at the time.

Now I needed to find new and comprehensive writeups of the principal and so I found the SpenceKonde
megaTinyCore for the new at the time tinyAVR 0/1/2-series IC’s. The core has a lot explained over the years and was very helpful and easy enough to understand but took a bit of time and real world practical implementations which made learning way more fun and easy. I always need to do practical with theory when it comes to learning I find it very hard to picture learning anything without using it practically.

Now this is about port manipulation on the 328P and I’ll get into the actual implementation now without further ado.

The ATMEGA 328P has 3 ports namely B, C, D with B (digital pin 8 to 13), C (Analog input pins) and D (digital pins 0 to 7).

For the basics you only need to understand 3 types of registers you will be manipulating.

For example:

Port B
PORTB – Maps to Arduino digital pins 0 to 7 Data Register – read/write
DDRB – The Port B Data Direction Register – read/write
PINB – The Port B Input Pins Register – read only

Port C
PORTC – Maps to Arduino digital pins 8 to 7 Data Register – read/write
DDRC – The Port C Data Direction Register – read/write
PINC – The Port C Input Pins Register – read only

Port D
PORTD – Maps to Arduino digital pins 14 to 19 Data Register – read/write
DDRD – The Port D Data Direction Register – read/write
PIND – The Port D Input Pins Register – read only

So an example using DDRD (Data Direction Register) to set input and output pins:

example using DDRD
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//
DDRD = 0b11111110;  // sets Arduino pins 1 to 7 as outputs, pin 0 as input
DDRD = DDRD | 0b11111100;  // this is safer as it sets pins 2 to 7 as outputs
                          // without changing the value of pins 0 & 1, which are RX & TX

Another example is to set digital pins 7,5,3 high:

set digital pins high binary example
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//
PORTD = 0b10101000; // sets digital pins 7,5,3 HIGH

Now you can do port manipulation with a bit shift instead of binary or hex. this makes things a bit more readable… excuse the pun. 🙂

For example to set the input or output of a single pin you could use:

input or output example
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//
DDRB |= (1 << PB3);//replaces pinMode(DATA_PIN, OUTPUT);
DDRB &= ~(1 << PB3); //replaces pinMode(LEARN_PIN, INPUT);

Example using hexadecimal:

hexadecimal input example
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//
DDRC = 0x00; // Define all Pins As Input

Now to initiate a pullup on a single pin you could use:

initiate pullup
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//
PORTB |= (1 << PB3);//initiate learn pin pullup

Example using hexadecimal:

initiate pullup hexadecimal
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//
PORTC = 0x20; // Enable Internal Pull Up Resistor on Pin 5

Example using binary:

initiate pullup binary
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//
PORTC = 0b00110000;// Enable Internal Pull Up Resistor on Pin 5 and Pin 4

Looking at how to read a pin you can use the Input Pins Register PINB:

read pins example
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//
uint8_t alarmState = PINB&8;//read alarm pin 3, notice 8
uint8_t learnState = PINB&16;//read learn pin 4, notice 16
uint8_t pinValue = (PINB & (1 << PINB4)) >> PINB4;//read a 0 or 1

it is also possible to toggle a pin and there’s different ways. Some are faster then others:

toggle pins examples
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//
PINB = (1 << PB3);//toggle fastest
PINB |= (1 << PB3);//toggle 2nd fastest
PINB |= _BV(PINB5);//toggle 2nd fastest also
PORTB ^= 0b00100000;//toggle 3rd fastest
PORTB ^= (1 << PB3);// toggle 3rd fastest also
 
// ~70ns pulse using 4 bytes FASTEST
PINB = 0b00100000;//toggle
PINB = 0b00100000;//toggle
 
// ~130ns pulse using 2 bytes
PINB |= _BV(PINB5);//toggle
PINB |= _BV(PINB5);//toggle
 
// ~200ns pulse using 8 bytes
PORTB ^= B00100000;//toggle
PORTB ^= B00100000;//toggle

You can also easily write to a pin low or high:

write high/low example
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//
PORTB |= (1 << PB3);//write high
PORTB |= (1 << PORTB3);//write high with PORTB3
PORTB &= ~(1 << PB3);//write low

There’s also an atomic operation to writing low or high:

atomic writing example
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//
PORTB &= ~_BV(PB3); // write single pin (atomic op) write low
PORTB |= _BV(PB3); // write single pin (atomic op) write high

So now that we understand the basics we can get into making life easy by creating macros

Below are 4 functions made easy to iterate over all the pins in each port B, C, D

set_PIN_HIGH(pin);
set_PIN_LOW(pin);
read_PIN_STATE(pin);
toggle_PIN_STATE(pin);

This makes it easy to call the function without having to define the port each time and it’s still fast.

See the example below:

DIY macros example
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//
// LED pin masks
#define LP0  1<<0
#define LP1  1<<1
#define LP2  1<<2
#define LP3  1<<3
#define LP4  1<<4
#define LP5  1<<5
#define LP6  1<<6
#define LP7  1<<7
#define LP8  1<<0
#define LP9  1<<1
#define LP10 1<<2
#define LP11 1<<3
#define LP12 1<<4
#define LP13 1<<5
#define LP14 1<<0
#define LP15 1<<1
 
// pin mask array
uint8_t ledpin_mask[] = {LP0,LP1,LP2,LP3,LP4,LP5,LP6,LP7,LP8,LP9,LP10,LP11,LP12,LP13,LP14,LP15};
 
// turn on LED
void set_PIN_HIGH(uint8_t pin)
{
  if (pin < 8)
  {
       PORTD |= (ledpin_mask[pin]);
  }
  else if ( pin < 14)
  {
       PORTB |= (ledpin_mask[pin]);
  }
  else
  {
       PORTC |= (ledpin_mask[pin]);
  }
}
 
// turn off LED
void set_PIN_LOW(uint8_t pin)
{
  if (pin < 8)
  {
       PORTD &= ~(ledpin_mask[pin]);//write low
  }
  else if ( pin < 14)
  {
       PORTB &= ~(ledpin_mask[pin]);//write low
  }
  else
  {
       PORTC &= ~(ledpin_mask[pin]);//write low
  }
}
 
// read button
uint8_t read_PIN_STATE(uint8_t pin)
{
  if (pin < 8)
  {
       //uint8_t pinValue = (PIND & (ledpin_mask[pin])) >> ledpin_mask[pin];//read 1 or 0
       uint8_t pinValue = PIND & (ledpin_mask[pin]);
       return pinValue;
  }
  else if ( pin < 14)
  {
       //uint8_t pinValue = (PINB & (ledpin_mask[pin])) >> ledpin_mask[pin];//read 1 or 0
       uint8_t pinValue = PINB & (ledpin_mask[pin]);
       return pinValue;
  }
  else
  {
       //uint8_t pinValue = (PINC & (ledpin_mask[pin])) >> ledpin_mask[pin];//read 1 or 0
       uint8_t pinValue = PINC & (ledpin_mask[pin]);
       return pinValue;
  }
}
 
// read button
void toggle_PIN_STATE(uint8_t pin)
{
  if (pin < 8)
  {
       PIND = (ledpin_mask[pin]);//toggle fastest
  }
  else if ( pin < 14)
  {
       PINB = (ledpin_mask[pin]);//toggle fastest
  }
  else
  {
       PINC = (ledpin_mask[pin]);//toggle fastest
  }
}
 
//example of using it
void StartUp()
{
  for(uint8_t i = 0; i < LED_AMOUNT; i++)//
  {
    tone(D_SPEAKER_PIN, D_NOTE_HIGH);
    set_PIN_HIGH(LEDS[i]);
    delay(D_DELAY_TIME);
    noTone(D_SPEAKER_PIN);
    set_PIN_LOW(LEDS[i]);
    delay(D_DELAY_TIME);
  }
}

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Electronics, Programming

328P PIN CHANGE INTERRUPTS

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#120 ATMEGA 328P Pin Change Interrupts

The 328P has 3 ports B, C, D you will need to know the basics of how they work to before reading this.

The 328P only has 2x external interrupts however there are also 23x pin change interrupts and I will be focusing on the latter for now.

INTx (external interrupts) can report events under four situations: low, any, falling, rising. PCINTx (pin change interrupts) can report events on only one situation: any, which is basically a change in the pin so we can categorise the 23x as change interrupts only.

Using these pin change interrupts are surprisingly easy but require a few steps. However once they are configured code size and complexity can be reduced significantly. Also never forget you paid for the IC and it’s hardware peripherals.. so USE THEM.

You can run a loop checking button states with multiple variables including timing and state variables etc. or…. you can run a similar reduced loop with the use of the pin change interrupts making your life so much easier while not compromising much resources.

So to get started you need to follow 3 steps:

  1. Turn the pin change interrupts on
  2. Choose the pins to interrupt
  3. Use the ISR for the chosen pins

STEP 1:

To turn on the pin change interrupts you will need to use the PCICR register.

Writing 1 to bit 0 will turn on the portB (PCINT0 – PCINT7)
Writing 1 to bit 1 will turn on the portC (PCINT8 – PCINT14)
Writing 1 to bit 2 will turn on the portD (PCINT16 – PCINT23)
From bit 3 onwards (from right to left) bits are ignored.

turn on the pin change interrupts
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PCICR |= 0b00000001;//PCIE0 // turn on port b
PCICR |= 0b00000010;//PCIE1 // turn on port c
PCICR |= 0b00000100;//PCIE2 // turn on port d
PCICR |= 0b00000111;//ALL   // turn on all ports

STEP 2:

Now you need to choose which pins you want to interrupt.
You will need to use a mask and the 328P has 3 masks: PCMSK0, PCMSK1, and PCMSK2
These masks are set in the same way as the PCICR register was set.

choose pins to interrupt
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PCMSK0 |= 0b00000001;// turn on pin PB0, which is PCINT0, physical pin 14
PCMSK1 |= 0b00010000;// turn on pin PC4, which is PCINT12, physical pin 27
PCMSK2 |= 0b10000001;// turn on pins PD0 & PD7, PCINT16 & PCINT23

STEP 3:

Now you need to use the correct ISR for the chosen pins.
make sure to keep the ISR as fast as possible and use as little code as possible in the ISR.
Also if you have any variables in the ISR make sure to make them volatile. This tells the compiler that it could change at any time and to reload it each time instead of optimizing it.

choose correct ISR
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ISR(PCINT0_vect){}// Port B, PCINT0 - PCINT7
ISR(PCINT1_vect){}// Port C, PCINT8 - PCINT14
ISR(PCINT2_vect){}// Port D, PCINT16 - PCINT23

Full Super Simple Example:

simple example
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#include <avr/interrupt.h>
 
volatile int value = 0;//make var volatile
 
void setup()
{
cli();//disable interrupts
PCICR |= 0b00000011; // Enables Ports B and C Pin Change Interrupts
PCMSK0 |= 0b00000001; // PCINT0 choose pin PB port
PCMSK1 |= 0b00001000; // PCINT11 choose pin PC port
sei();//enable interrupts
 
Serial.begin(9600);//start serial
}
 
void loop()
{
Serial.println(value);//print value when interrupt is triggered
}
 
ISR(PCINT0_vect)// Port B, PCINT0 - PCINT7
{
value++;//increase value
}
 
ISR(PCINT1_vect)// Port C, PCINT8 - PCINT14
{
value–;//decrease value
}

Links:

Electronics, Programming

DIFFERENT PROGRAMMERS

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#118 A look at different types of programmers

Different programmers for different IC’s some work with others.. some don’t

Over the years I have used different programmers for PIC,AVR,ST,ESP and WCH microcontrollers from simple FTDI TX RX programming to more advanced PICKit 5 dedicated programmers.

All the different types have their pros and cons but by far the most used by me is the cheap FTDI and serial TTL types for example programmers using the CH340, PL2303 and FT232 IC’s

Though the PL2303 is outdated there’s still many floating around and certain applications require the IC like when interfacing with old radios.

PICKit3, PICKit3.5 and the new PICKit5

With that being said you may ask why do we need a dedicated programmer? Well it depends…

Using the cheap common options I just mentioned above is good enough for a hobbyist but when you design a product you want something that’s is reliable common and has a guaranteed life span with support for the foreseeable future so that you will always have parts available for projects and the programmer.

USBasp AVR Programmer using SPI
STM Programmer


WCH-LinkE programmer can also program STM IC’s

Another big point is uniformity, dedicated programmers will usually be using parts with certain thresholds and voltages + current etc. all that data will be kept constant and accurate while a cheap programmer will most likely have a huge threshold..

A very important point is the ISP + debugging. A dedicated programmer will be able to do programming and debugging easily with a few pins. While a cheap programmer will require more pins and many times 2x programmers… 1 for debugging and 1 for programming.

BUS PIRATE can program with SPI
Arduino Nano with built in CH340 IC for serial programming
A n old DIY programmer of mine based on the CH340N IC

Dedicated programmers also have full support by the IC company as long as you have an original also they offer some really useful features like the PicKit5’s blue tooth option and stand alone programming or changing of source binaries on a phone.

All you need is the programmer and a phone is optional if you need to change things like binaries but really you can give a pickit5 to any technician and they can easily update supported IC’s without needing to mess around on a desktop/laptop computer. This is a very useful feature.

Now there also are EEPROM programmers and true universal programmers that can do EEPROMS and MCU’s like the old TL866II Plus which has a list here of all the supported IC’s. These programmers work well and allow easy access for single IC’s some can also read and write when an IC is in circuit but others require de-soldering. These programmers are usually quite large with Zif sockets.

EEPROM Programmer CH341B
Universal programmer the TL866II Plus

Now I just mentioned a few examples there is much more to talk about but I’m not going to be writing books here…

Electronics, Experimental

DIY UPDI PROGRAMMER

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#117 A DIY UPDI plug and play board

Making fast and crude but reliable programmers

When getting into the new ATtiny series (tinyAVR-0 tinyAVR-1 tinyAVR-2 IC’s) of microcontrollers a few years ago I noticed how easy it had become to program them with only a few extra components.

I started out with just a 4.7k resistor and a cheap CH340 programmer. Then 3 wire hook-ups later I could easily program my IC’s. The only downside was that I had to sacrifice the UPDI pin to the dedicated Pin gods.. so I couldn’t use that pin unless I wanted to make my life more difficult.

Well this was okey for me and ever since I always have the UPDI pin open only for programming. So all my designs incorporate this principal. If I really need more pins I would use an affordable IO expander IC.

Now with that being said it’s all good and well programming with a mini rats nest… but I wanted to create a simple plug and play DIY programmer with commonly available parts and plug and play compatibility.

So I came up with a small circuit that’s easy to build on stripboard. I created a few versions over the years. Since I was the only one using this contraption I didn’t think of creating a professionally made PCB but that will come in future..

Front of the stripboard
Back of the stripboard

How do I use this?

Basically I solder the SMD package ATtiny to a suitable breakout PCB then I plug the ATtiny breakout PCB into my programmers female headers making sure the orientation is correct and presto all I need to do is upload my firmware. Then I can just remove the PCB and Plug it into my project

Simple and to the point… plus it’s been working for years.

Electronics, Experimental

DIY LORA MODULE

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#115 Making A DIY LoRa Module

2x DIY LoRa RFM95W modules with adapter boards.

When taking a closer look at the DIY aspect of lora I wanted to test LoRa peer to peer.. E.G multiple peers to one peer (NOT LoRa WAN) I noticed that the actual radio PCB is difficult to use when going the traditional through hole way… adapter boards do exist but are few and far between at least in SA. you can make your own for manufacture but then rather create your entire product PCB for manufacture.

Even with this drawback I was able to source old adapters for one of the very firs modules the: RFM95W. In South Africa we are mostly using 868Mhz although 433Mhz modules are around I don’t see them being super common in terms of LoRa modules.

The modules I used have a footprint for adding a female SMA connecter for easy antenna connecting.

Parts used:

  • 2x RFM95W 868Mhz LoRa module transceiver
  • 2x 3.3v active buzzer
  • 2x 1 pole dip switch
  • 2x TP4056 module with protection ICs
  • 2x ATtiny404 MCU
  • 2x NCV8163 3.3V LDO
  • 2x SSD1306 128×32 OLED
  • 2x 2pin 2.5mm JST battery connector
  • 2x Headers and jumpers
  • 2x 13400 3.7V 550mAh
  • 2x 10k resistors
  • 2x 220R resistors
  • 2x SOIC to DIP adapter PCB
  • 2x BC547 transistors
  • Some 0.9mm tin plated copper wire
  • Some 0.255mm PVC insulated wire
Soldering made slightly easier…

After checking the PCB I commenced with testing the devices. Unfortunately the test area has largely mountains terrain
the signal works really well and penetrates better through foliage on the mountains terrain but once there is a full on mountain in the way the signal stops. so in this retrospect the devices are better then a radio which was quite interesting but makes sense because data is being sent and uses less bandwidth then interpreting voice audio. Also the error checking for LoRa helps a lot.

Some more pros for the LoRa is that its a transceiver out of the box with RSSI functions included. Also for increased range and/or quality the spreading factor and signal bandwidth can be adjusted.

Although there’s many pros regarding LoRa I still tend to use simple 433.92 RF modules without issue at least in my situation with rural areas under about 3KM at and given point.

So it really becomes more of a cost factor than anything else. Although I’m happy selling a custom LoRa product for compatibility with LoRa WAN or some other requirement with a similar principal. Plain old generic RF is still cool in my book.

Back of one of the PCBs

Electronics

WACO GP16 REPAIR

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#114 Repairing a 2 year old Waco day night switch

Inside the module I noticed the relay has no cover on it and a resistor and MOV were kind of in the way of the relay terminals…

Recently I had a Waco day night switch start to show faulty signs. Namely once dusk came the relay in the device would oscillate very fast for a few seconds effectively switching the light on/off very fast making a racket while stressing the LEDs out.

The relay would finally settle… mostly on the ON setting but sometimes it would settle on the OFF position. Then if you slightly bang the relay it would oscillate and settle on the ON position.

So I removed the switch and notices there was a lot of spider webs and critters close to the external AC connections. I cleaned the outer case and also notices a brown burn mark where the relay was located. This was due to sparks from the constant ON/OFF switching since the relay in this module had no cover.

The PCB was covered in a white powdery substance.

Now technically I did not have to open the module but I wanted to see if anything else was damaged. I opened the module and everything looked good except for the relay contacts which looked a bit beat up but were working ok..

I noticed that a resistor and a varistor were very close to the relay and could technically jam it’s opening/closing capability so I moved then away from the contacts and put everything back together again.

I now tested the module again and voila there is no more oscillations. So the grimy critters on top of the AC leads and the resister MOV combo close to the relay contacts were the likely culprits however my money is on the latter. So on re-installing I added extra tape and some silicon to seal the AC terminal blocks completely. A thin layer of silicone can still easily be removed for further maintenance and/or repair.

Testing the module to make sure the relay is getting the correct voltage etc.
Electronics

MULTIMETER VOLTAGE ADJUSTMENT

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#113 2011 Major Tech MTD84 Voltage Adjustment

The old meter has been through various toolbox banging battles..
Guts of the old multimeter. Very crusty with lots of through hole components and electrolytic capacitors. I replaced a damaged button as well as adjusting the voltage.

I have had the Major Tech MTD84 multimeter for 11 years now. Before I went off to another city far away for my first job my father purchased it for me as a parting gift. It was a low to mid range meter at that time and seems to be currently discontinued.

Now my meter is beat up but it reads just fine for the may DC projects I make however the voltage started to drift and has slowly become less accurate.

Luckily there is a few variable potentiometers on the PCB which can be adjusted to bring the accuracy back up to spec again. They allow for the DC, AC and Temp values to be adjusted no current option from what I could see. Even though I have a few multimeters I still can’t seem to throw this old one away…

Adjustable pots found on the back for easy access. Though they are very crusty…

So in order to set the correct voltage I had to connect a known working accurate multimeter to a battery along with the faulty one. For this I used the aneng8009 which has very good current and voltage accuracy for a cheapie.. Know I slowly adjusted the voltage variable potentiometer until the volts were mostly the same on each meter. (even though the MTD84 only has 2 decimal places it’s still close enough)

Very cool now the old multimeter is not so bad anymore with all it’s through hole resistors and electrolytic capacitors… perhaps next time I’ll have to replace a dry capacitor.

Button replacement success.