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SoftStart / TRIACRamp library

License: GPL v3 Build Status Hit Counter

Generates TRIAC control pulse for soft start of motors used in circular saw, angle grinder and other DIY tools.

Implemented and tested for AVR-ATtiny85 @ 1MHz

Schematics of an embedded motor soft-start

Eagle schematics

Schematics of a plug in module for motor soft-start

Eagle schematics
The eagle files are here.

  • Instead of 330 Ω at PB0 you can use a series of 120 Ω with a 220 Ω with 10 nF parallel.
  • The current sense circuit is only required for the plug in soft start adapter mode (LOAD_ON_OFF_DETECTION is enabled) to detect power disconnect. In this case the current is limited to 2 A (~ 450 W) if you using 1N4004 diodes. For more power you may use 1N5004 instead and/or use 2 diodes in parallel.

How it works (after calling startRamp())

  • Wait for 8 zero crossings of zero crossing interrupt to synchronize timing and check for right frequency (50 or 60 Hz).
  • Output TRIAC pulse and decrease pulse delay from START_PHASE_SHIFT_DEGREES to 0 degree at every voltage zero crossing. The decrease amount is specified by the ramp speed trimmer, i.e. a voltage at pin 2.
  • After delay gets zero, output TRIAC pulse pulse at zero crossing of AC line. The multi pulse (3 * 250 microseconds) will cover small delays of current zero crossing.

Calibration mode

Calibration mode is entered, when the ADC value from the ramp speed trimmer is less than 4.
This mode outputs the timer counter value forever (at 115200 Baud (@1MHZ) at pin 6 / PB1) in order to adjust the 50% duty cycle trimmer. Both values must be the same. The output format is: <counterForPositiveHalfWave>|<counterForNegativeHalfWave>\n
You have to use an isolation transformer to safely read this value.
I have not yet tested it, but using two 1 MΩ resistors instead of the ramp speed trimmer should work too.

Fuse values

FUSE VALUES for embedded version, which requires fast start, since soft start must begin as soon as power is on.

  • Low=0X52 Int RC Osc. 8 MHz divided by 8 (default). 14 Clk + 4 ms startup (for fast startup).
  • High=0XDC BrowOut at VCC=4.3 volt
  • Extended=0XFF (default)

FUSE VALUES for plug in soft start adapter, i.e. LOAD_ON_OFF_DETECTION is defined, which means that CPU power is always on. You may use the default values or enable additional Brown-out detection eg. at 4.3 volt.

  • Low=0X62 (default) Int RC Osc. 8 MHz divided by 8. 14 Clk + 64 ms startup.
  • High=0XDC BrowOut at VCC=4.3 volt
  • Extended=0XFF (default)

Compile options / macros for this software

To customize the software to different requirements, there are some compile options / macros available.
Modify it by commenting them out or in, or change the values if applicable. Or define the macro with the -D compiler option for global compile (the latter is not possible with the Arduino IDE, so consider using Sloeber.

Name Default value File Description
LOAD_ON_OFF_DETECTION enabled SoftStart.cpp If enabled, the program does not start with ramp at boot up time, but waits for interrupt at LoadDetectionInput (pin 6). This is useful, if you want to build an plug in soft start adapter. It only starts working when the attached device is switched on, e.g. a load is detected.
START_PHASE_SHIFT_DEGREES 160 TRIACRamp.h Initial delay of TRIAC trigger impulse. Values from 0 - 180 degrees, but the extremes make no sense.
TRIAC_PULSE_WIDTH_MICROS 250 TRIACRamp.h Length of trigger pulse - 100 us is too small for my circuit.
TRIAC_PULSE_NUMBERS 250 TRIACRamp.h Amount of multiple trigger pulses if delay is less than total time of multiple pulses. This avoids flickering at small loads.
TRIAC_PULSE_BREAK_MICROS 400 TRIACRamp.h Length of break between (multiple) trigger pulses.

Modifying compile options

Changing include (*.h) files with Arduino IDE

First, use Sketch > Show Sketch Folder (Ctrl+K).
If you have not yet saved the example as your own sketch, then you are instantly in the right library folder.
Otherwise you have to navigate to the parallel libraries folder and select the library you want to access.
In both cases the library source and include files are located in the libraries src directory.
The modification must be renewed for each new library version!

Modifying compile options with Sloeber IDE

If you are using Sloeber as your IDE, you can easily define global symbols with Properties > Arduino > CompileOptions.
Sloeber settings

Pictures
ATtiny85 board Triac and heat sink
ATtiny85 board Triac and heat sink
Placement Placement
Placement with 100 nF and selfmade coil Placement with 200 nF
Before After
Before After with 100 nF (It runs for 6 years now)