LED-PWM

A program for ATtiny2313(A) to control LED lighting brightness using a rotary encoder.

Profiles

The program can be build in one for two profiles:

lena profile uses an ATtiny2313 chip
saxa profile uses an ATtiny2313A chip

The brightness levels and bounce periods are also different in the two profiles.

Pins

                        ATtiny 2313  (Lena)
                        ATtiny 2313A (Saxa)
                           ┌───┐ ┌───┐
            (RESET/dW) PA2─┤1  ╰─╯ 20├─VCC
                 (RXD) PD0─┤2      19├─PB7 (UCSK/SCL/PCINT7)
                 (TXD) PD1─┤3      18├─PB6 (MISO/DO/PCINT6)
               (XTAL2) PA1─┤4      17├─PB5 (MOSI/DI/SDA/PCINT5)
               (XTAL1) PA0─┤5      16├─PB4 (OC1B/PCINT4)
Encoder CLK  →  (INT0) PD2─┤6      15├─PB3 (OC1A/PCINT3)  →  LED
Encoder DT   →  (INT1) PD3─┤7      14├─PB2 (OC0A/PCINT2)
                  (T0) PD4─┤8      13├─PB1 (AIN1/PCINT1)
             (OC0B/T1) PD5─┤9      12├─PB0 (AIN0/PCINT0)
Encoder GND  →         GND─┤10     11├─PD6 (ICP)
                           └─────────┘

Fuses

Low: E4 (modified)

fuse	bits	value	state	description
CKDIV8	7	1	modified	8× prescaling disabled
CKOUT	6	1	default	clock output disabled
SUT	5..4	10	default	slowly rising power
CKSEL	3..0	0100	default	internal RC oscillator 8 MHz

High: DF (default)

fuse	bits	value	state	description
DWEN	7	1	default	debugWire disabled
EESAVE	6	1	default	do not preserve EEPROM when flashing
SPIEN	5	0	default	serial programming enabled
WDTON	4	1	default	watchdog safety level 1
BODLEVEL	3..1	111	default	BOD disabled
RSTDISBL	0	1	default	reset enabled

Extended: FF (default)

fuse bits value state description

(unused) 7..1 1111111 default

SELFPRGEN 0 1 default self-programming disabled

fuse	bits	value	state	description
(unused)	7..1	1111111	default
SELFPRGEN	0	1	default	self-programming disabled

To program the fuses, use fuse.sh:

avrdude -c usbasp-clone -p t2313 -B 250kHz -U lfuse:w:0xE4:m

Flashing

To flash the controller, use flash-saxa.sh or flash-lena.sh depending on the profile.

Operation

PWM

16-bit PWM channel A (pin PB3) is used in Fast PWM 8-bit mode to control the LEDs' brightness. The PWM frequency is 8 Mhz / 2⁸ = 31.25 kHz.

While, an 8-bit PWM could be used instead, 16-bit PWM allows more flexibility if needed.

The PWM levels are defined by the levels table locating in levels.asm file where each level value takes 2 bytes. levels.asm is generated by levels.py.

The true pulse width is by 1 cycle greater than the PWM level value.

The level value 0 does not switch off the LEDs completely. It corresponds to the pulse width of 1 / 256. In order to switch off the LEDs, the program turns off the PWM mode when the level index is 0.

To make the transistor open properly, the minimum pulse width should be about 3 cycles (375 ns), so, the minimal non-zero level value is 2.

Gamma correction is used for the level values. The gamma value, andlevel_count can be set in levels.py.

level_count = 23, gamma = 2.5:

Rotary encoder

A rotary encoder is used to change the PWM levels. It is connected to PD2 and PD3 pins of the controller.

When inactive, both encoder pins (clk and dt) have high level (logical one). The program waits until there's low level (logical zero) on both pins, then determines the rotation direction by noticing which of the pins turns to logical one first.

In order to mitigate contact bouncing, each signal level on the encoder pins should be kept at least for debouncing_period (100 µs).

Sleep mode

When the encoder is inactive for sleep_time (about 1 s), the controller enters the sleep mode.

If the PWM level is 0 (the LEDs are switched off), the deepest Power Down sleep mode is used. Otherwise, the Idle sleep mode is used allowing the PWM to work.

The pins the rotary encoder is connected to (PD2 and PD3) are also used as external interrupt sources (INT0 and INT1) which can wake up the controller from sleep when the decoder is turned.

The interrupts are disabled during normal operation and enabled during sleep.

formicant/LED-PWM