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

For the DIY method i prefer the toner transfer method.

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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    59 Discussions


    5 weeks ago

    Very good idea to associate soft start and simultaneous switching for vacuum!
    I'd like to experiment this circuit and to slightly modify it with an ACS712 and an opamp instead of the CSE187 which is difficult to find here in France. The board will then also be smaller to fit into the boxes, and I'll try to apply the separation rules between HV and LV. I have two questions:
    - does the saw current pass through R5 and C1 before the triac is opened by the Atmega? So should'nt those components be able to sustain some amps?
    - is it possible to share your software source so that it can be modified and adapted to my configuration? Thanks in advance,
    Denis (from France)

    3 replies

    Reply 5 weeks ago

    Salut Denis, merci pour les commentaires. Non le courant ne passe pas par R5,C1 avant que le triac ne soit ouvert. Je comprend qu'en France vous avez du 220/50hz et que les pieces ne sont pas toujours facile à trouver. Pour le code, il détecte le 50hz et se synchronise en conséquence, ca devrait fonctionner sans rien modifier. Par contre, ici je n'ai pas pu tester a 100% car je n'avais pas de source 220v/50hz et pas plus de scie 220v. Si ça ne fonctionne pas, mon code est en assembleur, je pourrais vous l'envoyer pour modification. Laissez moi savoir si vous avez d'autres qiestions. Peut etre en pv je ne sais pas si c'est plus rapide mais ici sur instructable les notifications de commentaires sont assez lent.


    Reply 5 weeks ago

    Hello Yannick,
    Merci pour votre réponse. Je comprends donc que le micro commence par ouvrir un peu le triac pour pouvoir détecter la mise en route de la scie dès qu'un courant commence à circuler?
    J'ai fait beaucoup d'assembleur dans ma longue carrière, pas de problème de ce côté pour moi :-), c'est très sympa d'accepter de me communiquer le fichier source. Mon mail dans ce cas : citizen.kane1(at)
    J'envisage d'autres réalisations basées sur ce principe de prises maître/esclave, en version connectée avec un ESP32 (mais en C/C++).


    Reply 5 weeks ago

    Oui au départ le triac est ouvert un peu. J'ouvre la meme chose pour 50hz. Par contre sur 230v le courant est moindre. Je sais pas si l'interruption va se déclencher. Sinon il faudra ouvrir un peu plus le triac en version 50hz. C'est la seule chose que je vois qui pourrait ne pas fonctionner vu que je ne l'ai pas essayé. Pour le reste, les triacs sur 230v il n'y a pas de problème.


    5 weeks ago

    Not to split hairs here, but the BTA-24 is rated to 25 A. To get a 30 A rating one could use the T3035H-6I by STM as well for only a $1 buck more.

    1 reply

    Reply 5 weeks ago

    I just read the datasheet. I dont know why i wrote 30 Amp. It's realy 25A. Thank for your comment.


    2 months ago

    Very clear well done, could you pls. tell me which program you used for the schematics,
    can you share that file?
    Much appreciated

    7 replies

    Reply 2 months ago

    Thanks for the fast response, do you mind sharing the Eagle files
    this way i can order the PCB, I have no clue whatsoever how to use Eagle.
    Much appreciated.
    Thanks again


    Reply 2 months ago

    You have all you need here. Download the gerber file. It's all you need to order pcb. Just upload the gerber file to a pcb manufacture. You can also see the final pcb by uploading gerber file here:

    Let me know if you have problem


    Reply 2 months ago

    Thanks Yanick, sorry to bother you i downloaded all the files except the .ZIp
    file, sorry missed it. If I get into trouble for sure I'll drop you a few questions.
    Thanks for the offer.


    Reply 2 months ago

    Hi Yannick
    Could you pls. verify the dwg. (Gerber), I ordered the pcb everything went well till I I got to the Triacs, the dim. are totally out of specs. According to the datasheet
    I should have a spacing of 5.4mm min. between each leg, while on the PCB its only 2.69mm & the drilling ~~0.87mm while each leg is phys.1.24mm.
    Any help would be appreciated
    Apropo: B1 is missing in the parts list. bridge diode


    Tip 2 months ago

    Just my 2 cents.

    1) I think it is better to draw the schematic in a better way, so that it can be understood easily at a glance. This means, for instance, that the "logic" flow goes from left to right. I'm speaking specifically about the power supply circuit (T3, IC2, ...) which at first I thought was an output; it took me some time to analyse it and understand it was the power. If you put it on the left side of the uC then it is obvious. NOTE: I'm not one that follows this 100% of times, but anyway this is an advice I think is worth remembering when drawing

    2) I did not measure the clearances, but it seems to me that your high voltage traces are way too close one another. For 230V, the minimum distance two traces should have is in the range of several millimeters (3mm, if I'm not wrong, and at least 6mm from the low voltage part). In your case some traces are way too close, which means it will fail sooner or later. And moreover the low voltage part is embedded into the high voltage one, so please consider it risky too. Luckily you will always use it when you are supervising it, so any flame can be detected instantly (you will, won't you?)

    As for the rest of the circuit, I was not sure about how you detect the current flowing in the saw. The only explanation I gave to it (but I cannot confirm, since no source code is provided) is that the atmel gives pulses and detect the current; when it senses current it increases the pulse duration. Does it work this way?

    Best regards

    1 reply

    Reply 2 months ago

    Thank you for your input. Yes my hot side was to the right. I mirrored that :) Very quick to do and if it can help some people why not.

    For my clearance may appears to be too close but honestly, i dont thing this will be a problem. Future will tell us.

    The current detection works like this. The atmel does't give a pulse. Atmel is waiting for a low to high coming from T4. low to high does an interrupt and start firing the triacs. When it pass from hi to low it stop the saw. check option and stop vacuum now or later.

    Thank you for the advice, nice day!


    Question 2 months ago

    Very good instructable and a great idea! Could this be modified to run the dust collector for 5-10 seconds after the main tool is shut off? Thanks!

    3 answers

    Answer 2 months ago

    I'm doing a 1.1 version and i'm thinking to add a delay of course. Was thinking to add 3 secondes ? is it enough ?


    Reply 2 months ago

    Thanks for your reply. Personally, I believe a little longer would be better. (6 - 8 seconds) This gives the dust collector enough time to clear out any remaining debris in the lines.


    Reply 2 months ago

    Done, i added 6 seconds optional at the end on v1.1