All posts by Per Magnusson

Fixing the third brake light on a Toyota Avensis

This article describes how I fixed a non-functional third brake light of a Toyota Avensis Wagon. This light is centrally located in the spoiler of the rear door and it is not obvious how to remove it.

To get to the light, open the rear door and unsnap the trim in the red box in the photo below by carefully prying at the left and right edges.

Unsnap the middle trim and remove the rubber covers on the holes at the sides.

Remove the two rubber covers in the corners of the door, indicated by circles. They are already removed in the photo above.

The removed trim showing its snap points. (The part number is 64790-05040.)

Unscrew the four nuts in the circled holes. Be careful not to drop the nuts inside the door. Unplug the connector in the red box by pressing down on the locking mechanism and pulling the halves apart.

Four nuts to unscrew and a connector to disconnect.
Press down on the locking mechanism indicated by the arrow before pulling out the right connector.
Then press together the two harpoon pins of the bushing and push it through the hole.

The spoiler is held in place by the four nuts that were just removed as well as with a few snap pins. Close the rear door and carefully pull the spoiler up so that the snap pins let go. Also be careful that the cable for the brake light does not get stuck in the hole when lifting off the spoiler.

The hole pattern for the spoiler and brake light cable.
The removed spoiler with the brake light cable hanging out. The arrows show the slots where the screws holding the brake light are located.

Remove the two screws holding the brake light.

The spoiler without the brake light showing screws and snap points. (The part number is 76085-05060.)

If you want to just buy a new lamp, this is as far as you need to go with the disassembly. The part number for the lamp is 81570-05110 and it seems to be available from (no affiliation) or probably from your local Toyota dealer (at three times the price in my case). I managed to repair the lamp, so I did not have to buy a new one.

The cable can be removed from the light. It is secured in place by a locking mechanism, so the lever pointed to by the arrow needs to be pressed in to detach it.

Removing the cable from the light requires pressing the lever at the arrow.

Now the hard part begins. The light is not made to be taken apart. It seems to be glued or welded together. I managed to separate the outer lens from the base by first heating it all up to 90 degrees (do not go higher, or it will deform) and then using a knife to pry the pieces apart. I do not know if this generally works or if I was lucky. There is a significant risk that the outer lens cracks.

Another, perhaps safer, but less elegant way is to use a Dremel or similar with a cutting disk to cut the pieces apart. This is less likely to crack the brittle transparent plastics, but does of course leave a larger gap to fill with glue when the unit it to be reassembled.

(I had to resort to the Dremel method the second time I took it apart since I had then glued it together with super glue (CA) which did not otherwise give up its grip. See further below.)

The outer lens has been separated from the base. Tricky operation.

The difficulties are not quite over yet. Inside the base part, there is an inner lens that spreads out the light and holds the PCB with the LEDs. This lens is held in place by a hidden claw on each side and it needs to be removed so that we can get to the PCB. The photo below points to the claws.

Claws holding the inner lens and PCB to the base.

The way I managed to remove the lens was to put a screwdriver in the middle and bend the central part of the lens forward. It would probably have helped to simultaneously push inwards on the lens from the left and right, but I did not know retention mechanism at this point. For me, the front piece of the lens cracked in one place and then it was easy to remove. The crack did not matter since the lens was held together by the rear part, so it was still in one piece.

The PCB with the LEDs slides into the lens, see the rectangle below. It can easily be removed.

The PCB is held by the lens. The part number for the whole light assembly is 81570-05110.

The PCB is covered with dense white solder mask, so the trace pattern is hard to see. However, the circuit seems to be essentially a series connection of four LEDs and some current limiting resistors.

I tried to power the circuit with 12 V from a current limited lab supply, but nothing happened, as expected. After some inspection, I noticed that one of the LEDs had a cracked solder joint.

Cracked solder joint on one of the LEDs.

After fixing this, the light started working! Be careful not to use the wrong polarity when powering the light. The polarity is clearly marked on the board.

Working light!

I put the PCB back, glued the outer lens to the base using CA glue (turned out to be a mistake later) and reassembled the parts to the car.

Gluing in progress.

A few days later I discovered that the brake light did no longer work. :-(

So I had to disassemble the whole thing again and this time it was even harder to remove the outer lens from the base of the light since my CA glue did not want to let go. I tried to heat it up to 110 degrees C, but this slightly deformed the assembly, so that was a mistake. It also did not soften the CA glue enough to allow removal of the outer lens.

I had to resort to the Dremel method to separate the lens from the base.

I discovered that two of the LEDs were broken. I do not really understand what caused this failure, but I noticed the lenses of the LEDs were very soft. A wild speculation is that the fumes from the curing CA glue did mess with the LED lenses and caused the parts to fail.

I decided to replace all the LEDs. They come in a package called PLCC-4 and has the anode connected to three pins and the cathode to one (marked by a bevel). I found that LSE6SF-V2BA-1-1 from Osram seemed to be a good replacement, so I bought a few of these (from TME, but they are also available at Farnell and other distributors). It is of course important to get the rotation right when installing the new LEDs. The little bevel exists on both the old parts and the new, so carefully note where the bevel is and place the new LEDs with the same rotation.

One thing I noticed is that the inner lens that more or less grabs around the LEDs is rather tight and tries to push the LEDs towards the center of the board. Maybe this is what caused the original cracked solder joint. To make this less of a problem, I installed the two outer new LEDs a fraction of a mm closer to the center of the board, rather than centered on their footprints. This seems to cause less of an interference between the inner lens and the LEDs.

PCB with new LEDs.

A quick test shows that the light is again in working condition.

It works again.

Now there was a bigger gap to fill when gluing the parts together, so I used hot glue. First I pre-heated the parts to 90 degrees to give the glue a better chance to get a good grip and then I applied the glue and quickly put the pieces back together.

This time the repair seems to be more durable, even though it is a bit ugly if you look very closely due to the deformed plastics and hot glue. But it works and it should pass the yearly inspection.


Den 27:e mars till och med 24:e april pågår min utställning av träslöjdsföremål på Slöjdens hus i Skövde. Temat är: “Traditionellt hantverk möter ny teknik” och jag visar bland annat upp föremål som vakuumstabiliserats, datorfrästs eller fått Lichtenbergfigurer med hjälp av högspänning.

Här är en film som demonstrerar dessa tekniker. Filmen visas även i utställningslokalen och är med flit ljudlös.

En digital vernissage hålls på Facebook den 27:e mars kl 11:


Head lamp charging timer

This article describes a simple timer that disconnects a number of lithium ion batteries from their chargers after a predetermined time. The timer consists of a Teensy LC (Arduino compatible) processor board, a 2×16 alphanumeric LCD, MOSFETs to connect/disconnect the chargers and batteries and a few 3D-printed parts.

The timer with connections for four chargers and batteries.

Why it is needed

The youth section of my local orienteering club has a few head lamps to lend out during trainings to kids who do not have their own. The batteries need to be charged after each use, but it might be several days or even weeks before the leaders are back at the club house to disconnect the batteries from the chargers. There are reports of accidents where the chargers or batteries have caught fire in situations like this, so it would be good if the charging time could be limited.

The first idea was to put a timer on the mains supply to the chargers. After a quick investigation, I noticed that the chargers actually consume current from the batteries when they are not plugged into mains (an LED on the chargers is even lit in this case), so this was not a good solution as the batteries would be empty after a week or two in this state.

Instead I decided to build a timer that interrupts the DC connection between the chargers and batteries rather than the mains supply to the chargers.


As the processor board I decided to use a Teensy LC board, which is a pretty small and inexpensive “Arduino compatible” board (i.e. it can be programmed in the Arduino environment) with an ARM Cortex-M0+ processor. It has 27 I/O pins, which is more than enough for this simple application. The Arduino/Teensy environment provides useful and time-saving libraries for controlling the alphanumeric LCD, doing switch debouncing and keeping track of the time.

As the user interface, I decided to use a 2×16 LCD together with four push buttons. The LCD can be used in either 8-bit or 4-bit mode and I opted for the 4-bit mode since it requires fewer wires to be soldered between the Teensy and the LCD. The LCD also needs a potentiometer to control the contrast. Without that, or with the wrong setting of the pot, it will probably not show any characters at all.

I connected four momentary closing push buttons between pins on the Teensy and GND. By enabling internal pull-ups on these pins, no resistors are needed – reducing the amount of soldering required.

All of the pieces described so far are mounted to the back of a 3D-printed front panel as shown in the photo below.

Back side of the front panel with push button board (top), Teensy floating above the LCD and a USB connector (bottom left).

The USB signals are brought out to a separate mini-B connector mounted so that it is close to the side of the enclosure. The LCD is powered directly from the USB 5-V line. The 10-kohm potentiometer that provides the contrast signal to the LCD is connected between the LCD VCC pin (5 V) and GND. The push buttons are soldered to a scrap piece of perf board which is screwed to the front panel. Since the Teensy LC board is so small and lightweight, it works fine to just have it hanging in its short wires behind the LCD. An alternative would be to solder a few unused pins of the Teensy to the perf board.

The connection between the pieces are so few that they can rather easily be determined from the photo above. The code shown at the end of this post also defines which pins are used for what on the Teensy.

One pin of the Teensy controls the MOSFETs via the orange wire in the photo above. The MOSFETs are located on a separate piece of perf board, where most of the soldering in this project takes place:

The board with the six MOSFETs and associated circuitry.

I used MOSFETs I had on hand, but unfortunately, I did not have six identical ones, so one of six channels is equipped with a different kind of transistor. The schematic for each of the channels is shown below:

Schematic of one channel.

I did not want to control the MOSFET (M1) with the 3.3 V signal coming directly from the Teensy, since it might not turn on well enough with just 3.3 V. Instead I used a pull-up (R3) to the roughly 8-V voltage coming from the charger. When the NPN transistor Q1 is on, it pulls the gate of M1 low and thus turns it off and disconnects the battery from the charger. When the Teensy pulls the DISCONNECT signal low, the base current of Q1 (coming via R1) is diverted so that Q1 turns off and R3 can pull the gate of M1 high. Thus M1 turns on and connects the battery to the charger.

There is just a single DISCONNECT signal from the Teensy, connected to all the channels. The channels also share the same GND.

The Teensy is powered via a separate USB cable, so there could be a situation where the Teensy is unpowered, while there are chargers and batteries attached to the timer. I wanted the batteries to be disconnected from the chargers in this case and that is the reason for the diode D1. When the Teensy is unpowered, any of its pins will probably be about a diode drop (ESD diode) above GND if a small current is flowing into the pin. This might be a low enough voltage to prevent Q1 from turning on and M1 would be on, which I do not want. By adding the diode D1 in series with the DISCONNECT signal, we can be pretty sure Q1 will have enough base current to be on even when the Teensy is unpowered, and thus the batteries will be safely disconnected from the chargers in this case.

The MOSFETs I used (mostly STD35NF06T4) as M1 are vastly overkill in that they can handle much larger currents and much higher voltages than what will actually be needed here, so cheaper and smaller devices would work just as well. But I used what I had on hand that would fit the bill and I found no smaller suitable devices in the junk bin.

The processor connects to the MOSFET board with just a GND wire (black) and a DISCONNECT wire (orange).

To connect the chargers and batteries to the timer, I used extension cords that were supplied with the headlamps, but which are not really needed when the lamps are used for running at night. I cut these cables in half and soldered them to the MOSFET board. Unfortunately only four such cables were available, so I will have to add two more in the future to enable channels five and six.


As the main part of the enclosure, I used a CU-1874-B box from Bud Industries, but as mentioned above, I replaced the lid with a custom 3D-printed part I designed in Fusion 360. It has screw posts for the display and for the board with the switches, as well as rectangular walled holes for 3D printed buttons that push on the switches. The front also has some reinforcements to make it more sturdy, although it gets pretty sturdy anyway when the LCD and the switch board have been screwed into it.

Back side of front panel.

I designed the screw posts so that M2.5 (for the LCD) and M3 (for the switch board) screws could be self-threaded into them. The holes are square with sides of 2.1 mm for M2.5 and 2.6 mm for M3. The entrances of the holes are chamfered to make it easier to start the threads.

To mount the MOSFET board to the bottom of the box, I 3D-printed a frame (also with screw posts) that I then glued to the bottom of the box using CA glue. This way I did not have to drill any screw holes in either the front or the bottom of the box.

The frame for holding the MOSFET board.

I wanted to have proper strain reliefs on the cables and I 3D-printed those to fit all six cables at once. Again with square holes to allow M3 screws to self-tap into the material.

Strain relief for six cables.

Even though no screw holes were needed in the box, there still had to be holes for the cables and for the USB connector to power (and if necessary reprogram) the Teensy. Since I have a CNC machine, I used that to mill these holes. The cable holes could easily have been made with simpler tools, but the wall around the USB hole had to be thinned for a proper fit of the connector and this was easier done with the CNC than with alternative methods.

The box with holes.


The program running in the Teensy is a simple Arduino “sketch”. The LiquidCrystal library is used for communication with the LCD and the Bounce2 library is used for button debouncing. Time is kept by an elapsedMillis timer, a variable that automatically increments every millisecond.

The setup() routine – which is automatically called once at the beginning of an Arduino sketch – defines a custom LCD character (a right-arrow, play-symbol) used on the start screen to refer to the button to press to start the charging. It then sets up the I/O lines used for the four buttons; start, stop, increment and decrement. The line for the DISCONNECT pin and the on-board LED are set up as outputs.

The loop() routine is automatically called over and over again, indefinitely, in an Arduino sketch. In this case, it contains a simple state machine that keeps track of whether the timer is running or if it is stopped. If it is stopped, it only reacts to the start (or “play” if you will) button. By default, it starts a 15 hour countdown when play is pressed.

If instead the timer is already running, it will react to either increment, decrement or stop. Stop is self explanatory, while increment and decrement increase or decrease the remaining time. Initially the steps are 1 hour, but when the remaining time is lower, the steps are reduced accordingly. A maximum time of 48 hours have been defined earlier in the program.

When the timer is running, the LCD shows the remaining time in the format HH:MM:SS and this is updated every second. The LED is also toggled every second, although this will not be visible to the user as it is embedded deep in the opaque box.

Finally the program contains a few functions to help with showing information on the LCD.

Here is the complete code:

/* Head lamp charge timer.

   Disconnects a charger from a (head lamp) (LiIon) battery after a given time
   to reduce the risks of having a charger connected for a long time to 
   a LiIon battery.

   The user interface consists of a 2x16 LCD panel and some buttons.

   Target: Teensy LC
   Written by Per Magnusson,
   v 1.0 2021-01-08
   This program is public domain.

#include <Arduino.h>
#include <LiquidCrystal.h>
#include <Bounce2.h>

static const int32_t DEFAULT_TIME = 15*60*60*1000; // In milliseconds
static const int32_t MAX_TIME     = 48*60*60*1000; // In milliseconds
static const int32_t TIME_STEP    =  1*60*60*1000; // In milliseconds
static const int32_t TIME_STEP2   =    10*60*1000; // In milliseconds
static const int32_t TIME_STEP3   =     1*60*1000; // In milliseconds
static const int32_t TIME_STEP4   =       10*1000; // In milliseconds

// Stated
static const int32_t STATE_OFF = 0; // Not charging
static const int32_t STATE_ON  = 1; // Charging

// Pins
static const int START_PIN = 2;       // Start timer (and turn charging on)
static const int STOP_PIN = 3;        // Stop timer (and turn charging off)
static const int INC_PIN = 4;         // Increment timer by 1 hour
static const int DEC_PIN = 5;         // Decrement timer by 1 hour
static const int DISCONNECT_PIN = 12; // High disconnects charger from battery

// LCD           RS  E D4 D5  D6  D7
LiquidCrystal lcd(6, 7, 8, 9, 10, 11);

static const int LED_PIN = 13;

elapsedMillis timer;
uint32_t end_time;
int32_t state;

Bounce b_start = Bounce();
Bounce b_stop = Bounce();
Bounce b_inc = Bounce();
Bounce b_dec = Bounce();

// Custom character
byte play_glyph[] = {
const byte play_char = 0;

void setup() 
  lcd.begin(16, 2);
  lcd.createChar(play_char, play_glyph);
  b_start.attach(START_PIN, INPUT_PULLUP);
  b_stop.attach(STOP_PIN, INPUT_PULLUP);
  b_inc.attach(INC_PIN, INPUT_PULLUP);
  b_dec.attach(DEC_PIN, INPUT_PULLUP);

  timer = 0;
  end_time = 0;
  state = STATE_OFF;

  digitalWrite(DISCONNECT_PIN, HIGH);

  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, HIGH);
  digitalWrite(LED_PIN, LOW);
  Serial.println("Charge timer");

void loop() 
  static uint32_t last_update = 0; // The last time the display was updated

  if(state == STATE_OFF) {
    // Timer is off
    if(b_start.fell()) {
      // Start timer
      timer = 0;
      end_time = DEFAULT_TIME;
      state = STATE_ON;
      digitalWrite(DISCONNECT_PIN, LOW);
      digitalWrite(LED_PIN, LOW);
      last_update = 0;
  } else {
    // Timer is on
    if(timer > end_time) {
      // Time has run out
      state = STATE_OFF;
      digitalWrite(DISCONNECT_PIN, HIGH);
    } else if(b_stop.fell()) {
      // The stop button was pressed
      state = STATE_OFF;
      digitalWrite(DISCONNECT_PIN, HIGH);
    } else if(b_inc.fell()) {
      // Increment time
      if(end_time - timer < TIME_STEP3) {
        end_time += TIME_STEP4;
      } else if(end_time - timer < TIME_STEP2) {
        end_time += TIME_STEP3;
      } else if(end_time - timer < TIME_STEP) {
        end_time += TIME_STEP2;
      } else {
        end_time += TIME_STEP;
      if(end_time > MAX_TIME) {
	      end_time = MAX_TIME;
        timer = 0;
        last_update = 0;
    } else if(b_dec.fell()) {
      // Decrement time
      if(end_time - timer < TIME_STEP3 + 3 * TIME_STEP4) {
        end_time -= TIME_STEP4;
      } else if(end_time - timer < TIME_STEP2 + 5 * TIME_STEP3) {
        end_time -= TIME_STEP3;
      } else if(end_time - timer < TIME_STEP + 3 * TIME_STEP2) {
        end_time -= TIME_STEP2;
      } else {
        end_time -= TIME_STEP;
    if((state == STATE_ON) && (timer > last_update + 1000)) {
      last_update = (timer / 1000) * 1000;
      if(digitalRead(LED_PIN)) {
        digitalWrite(LED_PIN, LOW);
      } else {
        digitalWrite(LED_PIN, HIGH);

// Draw the splash screen
void lcd_splash()
  lcd.setCursor(0, 0);
  //         0123456789012345
  lcd.print(" Laddningstimer "); // Charging timer
  lcd.setCursor(0, 3);
  //         0123456789012345
  lcd.print("    Tryck "); // Press
  lcd.write(play_char);    // >

// Draw the screen showing that charging has finished
void lcd_done()
  lcd.setCursor(0, 0);
  //         0123456789012345
  lcd.print("    Laddning    "); // Charging
  lcd.setCursor(0, 3);
  //         0123456789012345
  lcd.print("      klar      "); // done

// Draw the screen showing that charging has finished
void lcd_stop()
  lcd.setCursor(0, 0);
  //         0123456789012345
  lcd.print("    Laddning    "); // Charging
  lcd.setCursor(0, 3);
  //         0123456789012345
  lcd.print("    avbruten    "); // interrupted

// Convert a positive number between 0 and 99 to a nul-terminated
// string with two digits. The first character is 0 for numbers below 10.
void int_to_00str(uint32_t num, char *str) {
  str[2] = '\0';
  str[1] = (num % 10) + '0';
  str[0] = (num - (num % 10))/10 + '0';

// Convert a positive number between 0 and 999 to a nul-terminated
// string with three digits. Leading zeros are replaced by spaces.
void int_to_3str(uint32_t num, char *str) {
  str[3] = '\0';
  str[2] = (num % 10) + '0';
  num -= (num%10);
  num /= 10;

  str[1] = ' ';
  if(num > 0) {
    str[1] = (num % 10) + '0';
    num -= (num%10);
    num /= 10;

  str[0] = ' ';
  if(num > 0) {
    str[0] = (num % 10) + '0';

// Update the countdown timer on the LCD
void lcd_update()
  uint32_t time_left;
  uint32_t seconds;
  uint32_t minutes;
  uint32_t hours;
  char sec_str[3];
  char min_str[3];
  char hour_str[4];

  time_left = end_time - timer; // ms
  if(time_left < 0) {
    time_left = 0;
  time_left /= 1000; // s
  seconds = time_left % 60;
  time_left -= seconds;
  time_left /= 60; // minutes
  minutes = time_left % 60;
  time_left -= minutes;
  time_left /= 60; // hours
  hours = time_left;
  int_to_00str(seconds, sec_str);
  int_to_00str(minutes, min_str);
  int_to_3str(hours, hour_str);

  lcd.setCursor(0, 0);
  //         0123456789012345
  lcd.print("    Tid kvar    ");
  lcd.setCursor(0, 1);
  //         01234567890123456789
  lcd.print("   ");
  lcd.print("    ");