Table Saw Soft Starter With Option Output




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 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 Files here

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.

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    88 Discussions


    15 days ago on Step 1

    Have to tried replacing the CSE187L for a ACS712 which is a far better product


    Reply 15 days ago

    Let me know


    Question 2 months ago

    Hi Yannick99
    Your design is best, I use 230v AC, it's relay difficult to find T3 FS12-090-C2 & T4 CSE187L in the UK , specially t3 , is it possible to use another components instead to do same things please.
    Thank you


    Answer 20 days ago

    Any simple basic transformer can be used T3 It can be quite a lot smaller as its only used for 5v supply to controller


    Answer 5 weeks ago

    Hi, sorry for the delay. For t3 you can use any 230v/12v. Just maybe check for the pad layout if hole are in same place.
    T4 is different. It's a current sense. Probably some other will do the job. But i can't recommend any. The spike on uC side must be high enough to fire the start.
    Check on ebay i saw some shipped worldwide.


    20 days ago

    Nice circuit can you not use a smaller simpler cheaper controller ?


    10 months ago

    I'm using 230VAC and the circuit behaves this way:

    When there's no load on the outputs (and pins 1,3,4 not connected anywhere):
    - Zero crossing detector give correct pulses to pin4;
    - Led 1 blink with barely visible light, LED 2 is dark;

    When switch on the table saw is put to ON:
    - after 3-5 sec the motor try to start like geting short pulses (LED 1 blink the same way as mentioned above).
    - sometimes after pulsating the motor start to run softly (like expected), both LED became normal bright) and then with full power. The voltage on the C7 rises from 0 to about 4V. Pulses on pin 12 correctly get wider and wider as motor goes to full power.
    - on other cases motor just pulsates erraticaly and finally stops. Voltage on C7 rises up to about 3V and then drops.
    SInce I cannot see the code I do not know how uC detect when the table saw is powered on. I assume that there should be some short trigering pulses on pin 12 to enable motor to start (means the T1 is totally opened). After switching the motor ON pulses from T4 should start the proces of soft start. Am I right? On osciloscope I can only see some very small spikes on pin12 which cannot triger the triac. Can you please let me know how the circuit should start?



    Reply 10 months ago

    hard to find just like that. I can give you the code:!AnKLPDy3pII_ul12b4-Mcu-K8IIG?e...
    The device trig on int1. You could try to rise the starting voltage. Now it's 900 (384). more the value is high less the voltage is. So try 850. On my side with 120V the current is higer than you so i dont need a huge number. You can open the file with atmel studio 7


    Reply 10 months ago

    Thank you for prompt response. I will try doing so.


    Question 1 year ago

    Hi Yannick
    I have problem, circuit working, no shorts no smoke, I'm trying the circuit with 2 light bulbs, line pad2 (saw) ramps up to it's 110v stays on for about 2 sec. then shuts down & restarts, line pad3 (vacuum) does not get to more than 25-30 volts, i have no jumpers on JP! at all. Any suggestions would be well appreciated.
    (maybe pad3 does not get to it's voltage because of pad2 does not stay on long


    Answer 1 year ago

    Hi Roger, this is normal with 2 a light bulb instead a real saw. When the saw is started, there are a sensing on pd3 to check if the saw is running. If not the uC reset. So, you are using a bulb and the current is too low. So pd3 is low and controller reset.


    Reply 1 year ago

    Didn't take long to test, Primary "PD2" works fine amazing soft start, secondary "PD4" does not respond at all with load on primary & without, did not check voltages.
    Your thoughts pls.


    Reply 1 year ago

    The 2 output are on PD6 and PD7 There are no PD4 and PD2 is an input not an input. So Primary (SAW) is PD6 and Vacuum is on PD7. Now if secondary isn't working (PD7) check the Led LD2. Is it turn on ? If yes problem is after the opto, if not problem is before like uC, solder, R7 or maybe the opto itself if the opto is in open state.


    Reply 1 year ago

    Thanks Yannick
    I'm lost here, my connections are as per schematics, lets forget primary & secondary (my error),
    I have Pad 6,3,1 to mains 115v, Pad 7 to neutral, Pad2 out1 to saw, Pad4 out2 to vacuum, Led1 comes on when saw is
    started, Led2 comes on when vacuum is connected but no juice. I switched between the 2 Moc21 & I'll check a bit later during the day. In the pictures i have black wires as line 115v Purple as PAD2,4, white as Neutral,
    ps. can i add that fan for the heat sink it's 25 ma @ 5volts or the transformer will be loaded?

    image1.jpgimage2.jpgUntitled (2).jpg

    Reply 1 year ago

    Ok you means PAD sorry. Because PD6 PD7 are uC pin. Sorry my error.
    Now for your problem. If both LED are responding it's good. The program is ok, the current sensing is ok. By default, LED 2 should be turning on delayed after LED 1. No need to connect vacuum. it should be working with no load.

    For connections, to be sure, Pad 6 3 1 to main, it's ok. Pad 2 and 4 to the outlet. Dont forget to cut the connection between both outlet on the hot side. And the 2 others side of the outlet go to neutral. I saw 2 white wire on your outlet, those cable need to be together. Dont need to cut the connection between outlet here. Only hot side need to be cut. Probably your purple cable are hot. So on this side cut the connection and not on the other side. If you cut the connection on both side just jump a cable on the neutral side (2 white cable together).

    For your fan. probably ok, try it. But you realy dont need a fan. You will add noise and dust for nothing. The thing doesn't get hot. And i saw your heat sink :) You will ok.


    Reply 1 year ago

    Thanks for commenting on the heat sink, Ok no fan, it does not warm at all after 10 min on out1 full load.
    Ok, swapped the moc21 to be sure that they are correct, and got the same results as before,
    Re soldered all the parts on board. nothing new here.
    Verified low voltage on OK3 nothing at all with or w/o load, OK2 voltage Ok
    The only way i could get it run is putting a jumper on JP1 position1 On (start same time as out1) & since JP1 pos.2 is off
    i get also soft start on too.
    For the outlet, yes i cut the hot side & the purple lines are independent, the neutral side is intact one white from the main & the second white is from T3 neutral Pad7.
    Is led1 supposed to be off when their is no load is off (Saw off)? Mine is dim but not off while led2 is totally off
    Have a great evening.


    Reply 1 year ago

    OK2 and OK3 are optocoupler. So the load and the LEDs are completely isolated. Trust the led. At start, led1 is dimmed. led2 is off, this is normal.
    Note that LED are reflecting the output. Led1 dim = output dimed. Led1 full on = output 120vac. Same thing for led2. If led1 is dimmed at start it's because we need a bit of voltage on the saw but not 120vac. Just a bit for starting.

    If you are able to see led2 turning on, (slow or not) and you dont have any current on output 2 you have a problem. Maybe triac ?

    Is led2 turn on sometime ? When ?


    Reply 1 year ago

    Hi Yannick
    I have no clue why but got it running without any jumpers, I get OUT1 softstart (saw) Out2 delay start which very good for me. Every once and then i get a hard start on OUT1 but if i restart the saw it's back to normal (soft start), I can manage with that.
    Thanks for all your support.
    best regards
    Apropo; that's the best softstart I tried to build, the other ones their was no current sensing & had to cut the line between the switch & motor to get them running.


    Reply 1 year ago

    Oh Nice. well done. Thank you for the gentle comment.
    If you find what was the problem tell me. Maybe helpful for other one.


    Reply 1 year ago

    With pleasure i would inform you, again thank you for the project, all the time & help you gave me.