Introduction: Table Saw Soft Starter With Option Output

About: Hi, i'm electronic technician but it's my hobby too. I like to do and try many projects just for fun :)

Hi, this is my new project. A Table saw soft starter with option output. This means, when you have something to cut with a table saw or miter saw or any power tools. This module detect when the load is turned on and send voltage from low to high in 3 seconds. It remove the huge spike at the beginning, lower startup current and very more quiet. No more breaker problem at startup. Very handy with generator. Some generator have limited startup current.

I have also added a second output to plug a vacuum, light or anything else. This output have different options. It can start at the same time of the saw or after. It can be soft start or hard (direct) and can also stop 6 seconde after saw has be turned off. These options can be chosen by connecting some pin to gnd.

So if i resume, you plug the saw (turned off) in saw outlet. You plug the vacuum (turned on) in vacuum outlet. When you turn on the saw, the saw will start slowly. As your option switch setting, the vacuum will start by itself. No need to turn this on. The module will send the voltage for you. When you will turn off the saw, the saw will turn off (of course) and the vacuum too. No need to touch at the vacuum anymore.

I was searching for this on internet. I found different soft start but some modifications was needed on the table saw. Like cut the power button to bypass the switch. I wanted something transparent. I finally found a module but without option output. You can see this module here. By the way as you can see the girl is very pretty :P On my side i dont have some pretty girls and Ferrari (see behind) to do my demonstration but at the end, it's doing exactly the same :)


0v ac to 115V/230V in ~ 3.2 sec

2 Outputs: Saw and Vacuum

Output 2 can be soft, hard, start and stop delayed

115V/230V same pcb, Only 1 layer pcb.

1 universal software for both version (115v,230v)

Device can Hold up to 25 Amp. (Triacs)

No external modification needed on saw

Board fit in a conventional electric box


Lost of approx 2v rms at the output. The triac are not like relay. it's not a mechanical contact.

Step 1: So Let's Begin. the Schematic.

I give you the image and pdf version.

There are 5 areas.

- The uC atmega328 is the controler for this projet. i'm using 3% of memory only. Why i choose a 328 instead a simple tiny ? Because those one are very very popular and cheap. Buy a arduino and you will get an atmega328. But i'm not coding with arduino ide. I'm using atmel studio.

- The Power supply. Nothing more that a regular linear psu. Bridge regulator et lowpass filter.

- The 0 crossing detector. When we work with ac and triac. We must know when trig or remove the trigger on the triac.

this is the job of H11AA1. This one send a pulse to uC when 0v is achieved.

- The current sensing module. We must know when we power on the saw. This is the job of the CSE187L

when a current pass throw the transformer, a voltage is coming at the output. Diode, lowpass and the zener 5.1v ensures that voltage will not cross higher than 5v.

- Output modules. optocoupler and triacs are limiting the current to the load.

Step 2: The Parts.

As you can see on picture, there are no very much parts. All those parts aren't obsolete and can be easily buy on digikey, mouser or even ebay.

This is the list: At the end is the digikey PN of the main component

B1 Bridge rectigier DF02MDI-ND

C1 0,02uf

C2 100uf 25v

C3 33uf 10v

C4 .1uf

C5 0,02uf

C6 .1uf

C7 1uf

D1 Zener 5.1v 1N5231B-TPCT-ND

D2 1N4148 1N4148FS-ND


IC2 7805TV 497-1443-5-ND




OK2 MOC3021M 160-1374-5-ND

OK3 MOC3021M 160-1374-5-ND

R1 1k

R2 33k

R3 220

R4 150

R5 1,2k

R6 2.2k

R7 220

R8 150

R9 1,2k

R10 33k (removed in version 1_1)

R11 1M

T1 BTA24 497-3124-5-ND

T2 BTA24 497-3124-5-ND

T3 FS12-090-C2 237-1577-ND

T4 CSE187L 237-1103-ND

You will need electrical boxes. So buy 2 and attach both boxes together. But at the beginning it's easier to have them split up. More easier to fix the board in place.

Also some wire. I recommend 18 awg for psu and 14 awg for triacs

Step 3: PCB, Gerber File or DYI Method

I'm giving you 2 choices. A diy PCB like i did. It's only 1 layer, no big deal. Or you can use gerber file to have a professional pcb. The .zip is gerber file. This file you need to upload to pcb manufacture. You can see the final result by uploading the file here

The gerber file isn't the same than diy pcb. There 2 layers for triac. Also trace space are a bit higher between each other.

For the DIY method i prefer the toner transfer method.

Impossible to upload gerber file. Internal server error so...

Gerber File

Step 4: Solder Component

As you can see, i added solder on pcb large wire. The current will be higher on those wire. It's also time to solder the larges wires. 18 awg for psu and 14 for triacs.

Step 5: Program the Atmega328

Plug in your USBasp or USBtiny device in your computer and let Windows detect the device (it will report driver not found). If a window pops up asking to search for driver, just close it or click on Cancel.

At this point, download and run Zadig, it should detect the USBasp or USBtiny, or any libusb device that you have. Then in the selection box (see picture), choose libusb-win32 (v1.2.6.0), click on Install Driver, and wait for the installation to complete. Check in device manager for atmel usb device = ok. No excalmation mark anymore Download SoftStart_code below on this page and unzip files in a folder. I create a batch file to program the chip with .hex and fuses bits at same time. Connect USBasp or USBtiny cable in your board, no need to plug the softstart in wall. Double click on program usbxxx.bat At the end, code and fuse bit are programmed.

You can use atmega328 or atmega328p.

Step 6: Preparing the Box

Remove the 4 screws. We will reuse those screws later. Put some nuts as spacer and add some plastic sheet (like picture) or if not, probably some electrical tape should be ok but try to find some plastic isolator first. Maybe on an old power supply. That's what i did.

Gangable electrical box.

Step 7: Bent Triacs, Thermal Paste

You need to bent a bit both triacs and add some thermal paste. With only a half of electrical box, fix the board and triacs. You will need to do 2 holes for this.

The triacs doesn't need to be insulate. BTA24 are stock insulate.

Step 8: Option Wires

4 little wire to connect the option switches. The option switches are optional.

If you add no jumper at all default of out 2 is: Soft start, delayed start and stop at same time of out1.

See next step for more details

Step 9: Install Outlet and Option Switches

With schematic help, install outlet. Be careful to put the Hot at the right spot. Connect also the ground earth to the outlet.

Important. You must disconnect outlet from each other by removing the tab between the outlet. See picture. Only hot side need to cut.

Like i said, The option switches are optional.


Pin1(pb4) to gnd = Out2 will start after Out1

If not = Out 2 will Start at same time of Out1

Pin 3(pb5) to gnd = Out 2 will Hard Start

if not = Out 2 will Soft Start

Pin 4(pb3) to gnd = Out 2 will continue 6 seconde after.

if not = Out 2 will stop at same time of Out1

If you add no jumper at all, default of out 2 is: Soft start, delayed start and stop at same time of out1.

Step 10: Is a 15 Amp Breaker Is Enough ?

A saw consume a lot of current. You can see here a full table saw review including amp current.

as you can see, it can varie from 7.8 to 24.1 amps

On my side, i'm only using a 15 Amp breaker and so far, working for me. The vacuum have almost 0 load and i doesn't cut hard wood.

But, best thing to do should be 2, 15 amp breakers. I'm not saying to use 240v here. I means one Hot and one neutral by output. It's 120v by output with 2 different breaker.

It's like a kitchen outlet. We can plug a toaster and a kettle in same time because each outlet have different breaker.

Now, if you have 230V/50Hz the current is a half. I dont thing that will be a problem for you.

Step 11: The End

I hope you have enjoys this project. At first i tough that this project should be easy to do. But i under rated some parts. The 0 crossing wasn't easy to deal with. It's not a sqare 0-5v output but sort of pulses so i spend some time with my oscilloscope to match the timing.

Also the current sensing part was time consuming too. I tried with some op-amp, with some wire pass throw a coil etc. At the end i found this transformer cse187l. And surprise the output was very strong. No need to add an op amp anymore.

230v is supported but... in north america we dont have 230/50 HZ. So program detect frequency. I tested with a frequency generator. But i dont have tested the whole thing in real life. If some of you did the project just confirm me if all is ok under 230v 50HZ.

Step 12: Demonstration With Saw and Light

As you can see the saw is starting slowly. I'm using a light bulb instead real vacuum for the demo.

Step 13: How It's Work

-As soon you plug the softstart in an outlet, the uC check the time between 2 zero crossing points.

-It's the way the uC know the frequency of the line, 50 Hz or 60 Hz and in the meantime the voltage it is dealing with. 50 Hz = 230V and 60 Hz = 120V

-Knowing that, uC send the good starting voltage on softstart power outlet. This starting voltage is different for 120 or 220v.

-It's why you see the opto led very dim when the saw is off. This is normal.

-When you turn on the saw power switch a current is appearing in T4. Doing a voltage spike through D2 and stay at high level until the saw is turned off. Zener diode protect the uC if voltage is too high. C7 is a low pass filter and transform the ac spike in DC. uC detect the high level and trig an interrupt.

In other word, when you turn on the saw power switch, 5v is on C7 and detected by the uC.

-Triac is trigged from 2% to 100% (duty cycle) in around 3 seconds and stay at 100% until the DC from T4 goes from hi to low.