Last chance to enter The Hackaday Prize.

Controlling an AC drill using one PWM connection

This peculiar setup allows [Ben Krasnow] to control an alternating current device using one pin on a microcontroller. He’s experimenting with a power drill and has relocated the trigger circuitry that makes it spin. On that board he found a variable resistor combined with a capacitor which control a triac, actuating the speed of a drill. [Ben's] solution works great and isolates the drill from the control circuitry. He replace the variable resistor with a cadmium sulfide¬†photoresistor¬†(basically a variable resistor whose resistance depends on the intensity of light). Pulse-width modulation is used to adjust the brightness of an LED shining on that photoresistor and thereby affect the speed of the drill. This is such as simple alteration to the drill we’d call it MacGyver-esque.

See a demonstration after the break.

Comments

  1. now that is just crazy.
    …but it works :)

  2. thatguy says:

    What’s the advantage vs. a MOSFET or power transistor?

  3. Iv says:

    @thatguy : the advantadge is that you don’t need a MOSFET or power transistor :-)

  4. osgeld says:

    cough 555 timer can pwm cough

    but nifty

  5. but a 555 does not have a serial connection to whatever you want ;)

  6. goldscott says:

    Neat “optoisolator” trick!

  7. minipimmer says:

    @thatguy, @lv the motor is still triggered by a Triac (I guess one as the machine may be powered by CC instead of AC) which already was in the original drill.

    This hack is nice clean and simple solution if you want to control the speed of the drill from a microcontroller.

  8. fjr says:

    This would be really great to hook up to a drill press or use to regulate the speed of a router motor for a cnc.

    Lathes would be another great application. Would a similar power system work for an induction motor? (probably not)

  9. chango says:

    Optoisolator and low pass filter with only two components. Sweet!

  10. Brad Hein says:

    SAW XXXII?

  11. Eric says:

    I really like this for what it is, but is there any relatively simple solution for speed control of motors like this? The triac circuit always seems to perform the worst when you most need it: for high torque at low rpm.

  12. Mike Szczys says:

    I suppose a dremel works the same way. I’ve got one with the slide-speed control so that must just be a wiper on a variable resistor. Would speed control be of any use in a CNC setup using a dremel?

  13. Whatnot says:

    He makes a tricky statement in the video, he says a cheap house lighting dimmer has the same circuit but that’s not true, the normal cheap lighting dimmers don’t have the zero crossing circuit and have a limited wattage capacity, so yeah you could control the light with the same hack but you should in such cases not connect a motor to it, those dimmers always have a warning that they are only for incandescent light too.
    On a related note, since everywhere people are switching to energy saving bulbs I wonder how long it will be before they stop selling those simple dimmers and we’ll get cheap dimmers of slightly higher complexity as standard.

    As for this nice hack, I would think it best to add this circuit and a switch to switch between the default resistor and an LDR/LED, and a small connector in the actual drill housing so you can simply plug and unplug the arduino and use the drill normally too.
    You’d have to make sure it’s the right switch (break before make), but most are, and it would be most convenient if ‘off’ is equal to the highest resistance though, which it most likely is I guess.

    Anyway it’s a moment of genius when he thought this up, so simple and yet you’d have to think of it eh.
    And so universal too, you can control most anything with a potentiometer with the LED/LDR trick, although you must be careful there are no glitches in the software when using it to control volume on a 600W amplifier for instance ;)
    And of course you’d need a LDR with the right range (my local shop has either 20K or 50K types only)
    And perhaps use a software profile for linear and logarithmic variants?

  14. Kaj says:

    Funny part – I haven’t watched the video, but the first thought I had was using it with a dimmer. It’d sure make that sunlight simulator circuit I wanted to build a lot safer/simpler to implement… I already have a dimmer.

  15. Hitek146 says:

    To dim a CF bulb, you wouldn’t necessarily need a different dimmer, just a different bulb. I haven’t looked myself, but the first stage to a CF bulb should be a rectifier, so the switching circuit should be being fed DC. Most switchers are designed to maintain a constant output voltage, even in the event of a varying input voltage, which, in my experience with dimmers and CFs, seems to be true. You would want the switching circuit in the CF bulb to slightly lower the output voltage at some ratio to the input voltage. Of course, at a certain dimming point, there will no longer be enough voltage to power the CF’s switching supply, so there would be fall off at the bottom end…

  16. Ben Ryves says:

    Nice work. :-)
    Speaking of light dimmers, Afroman used one to build a “cheapass professional soldering station” – http://www.afrotechmods.com/cheap/iron/iron.htm

  17. zeropointmodule says:

    nice use of old school tech..

    a little bit of history for you, the very early Heathkit sinewave oscillators used a circuit based on these to control amplitude of a Wien bridge..

    A modern equivalent would be a pair of back to back red LEDs and some sort of active feedback circuit based on a JFET and a phototransistor or a regular BFY51 can with its lid removed.
    relatively simple to implement as the transistor responds as if it is being biased in the conventional way.

    this particular hack was shared by a very helpful amateur radio enthusiast in the UK.

  18. Drone says:

    Ahhhh, now this is why we come to HaD…

  19. pRoFiT says:

    The savemart by my house has dimable cf bulbs 2 for a $1.00.

    Wouldn’t an optocoupler work better in this situation. That way outside light would not effect the speed.

  20. ocs says:

    finally a cool hack

  21. Jessika says:

    This is exactly what I am trying to do. All the companies have told me that an Arduino is not the best fit for controllling an AC motor, so im wondering how did you go about controlling the motor. Also what exactly are you doing to control the brightness of the light, do you have a manual control or automatic?

    Lastly I know you weren’t worried about the direction of the motor, but if you have any ideas about how to control the direction as well.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 91,175 other followers