Piezoelectric Crystal Speaker for Clock Radio Is Alarmingly Easy to Make

cockadoodledooLet’s face it: most of us have trouble getting out of bed. Many times it’s because the alarm isn’t loud enough to rouse us from our viking dreams. [RimstarOrg]’s homeowner’s association won’t let him keep a rooster in the backyard, so he fashioned a piezoelectric crystal speaker to pump up the volume.

[RimstarOrg]’s speaker uses a Rochelle salt crystal strapped to a bean can diaphragm. In his demonstration, he begins by connecting an old clock radio directly to the crystal. This isn’t very loud at all, so he adds a doorbell transformer in reverse. This is louder, but it still won’t get [RimstarOrg] out of bed.

Enter the microwave oven transformer. Now it’s sufficiently loud, though it’s no fire bell alarm. He also demonstrates the speaker using a piezo igniter from one of those long barbecue lighters and a crystal radio earpiece. As always, the video is after the jump. [RimstarOrg] has a lot of relevant linkage in the summary so you can learn how to grow your own Rochelle crystals.

[via Dangerous Prototypes and Hacked Gadgets]

33 thoughts on “Piezoelectric Crystal Speaker for Clock Radio Is Alarmingly Easy to Make

    1. Yeah. Forget the piezo crystal. Just hook up the microwave transformer transformer to the bedsheets through some metallic thread. Will work lots better than just a little beeping.

  1. I know some people have a hard time getting out of bed, but think of your neighbours :D Every morning i have to live with my neighbour turning on his radio in his bedroom (which is adjacent to mine). It’s really annoying :)

    1. You find yourself sitting in the corner thinking if your neighbor ever did have a snooze button on his forehead.

  2. I, too, have this clock radio. When I sleep, I sleep like the proverbial dead. This model has been the only alarm to consistently wake me over the last 10 years. Great mod.
    I’d miss the characteristic “Woo” of the normal speaker, though.

  3. The sad part of this is that the original speaker was probably many times louder than any of the piezo speakers. Also, a simple LM386 would have done a much better job amplifying the audio signal than those lossy transformers did.

    +1 for creativity, -1000 for efficiency.

    1. Not so. The LM386 could only amplify as much as the input voltage. The transformers in reverse would have bumped the voltage to hundreds.

      1. Tell you what. Take a proper 8 ohm speaker, and hook it up to a properly constructed LM386 circuit. Now hook the same speaker up to a MOT and compare the two.

        Get back to me once you realize what I already know from having done exactly that.

        1. The point in this case, is that piezo speakers are very high impedance. They function better with high voltages, and don’t draw a lot of current. IE the opposite of the 8 ohm speaker the alarm clock originally drove. So the transformer is matching the impedance, to put it one way. Driving the piezo more efficiently. So just by itself it will help a lot.

          An LM386 in front of the transformer may help, or may not, depending on what was driving the 8 ohm speaker in the first place. Which is ultimately limited by the DC supply voltage. But the transformer would do a much better job in this case than an LM386 without an output transformer.

          In your original post on this subject, a couple of posts up, you say an LM386 would do a better job amplifying the signal than the transformer does. In a way, you’re right, since the transformer isn’t there to amplify. But amplification is not what’s needed to get more loudness in this case, it’s impedance matching. So unless you want to argue about the specific use of the phrase “amplifying the audio signal” being separate from “making it sound louder”, then you’re wrong.

        2. I don’t really remember reading that an 8 ohm speaker existed on your first post. For all I know it was the rochelle-salt driven speaker we’re talking about (as is that hack above.) The fact that the rochelle-salt speaker is a form of a piezoelectric speaker, a high voltage source would be the better option for this. I’m not saying you are wrong in what you’ve tried, but you replaced the subject of using the piezoelectric speaker here to suit what you suggested (of using an LM386.) If it were an 8 ohm speaker, I wouldn’t have thought twice of using an LM386 myself.

      1. I will admit to spending time deciding whether to make the screenshot at 6:59 or 7:00. And then “I Got You Babe” started up in my head.

        1. Let’s be honest… you knew this was already posted but couldn’t resist making the “Alarmingly Easy to Make” pun. :)
          What’s it say about Brian that he chose 6:59?

  4. Here in Indiana we are chronologically impaired as it only gets light at 8:00 AM right now. We are on DST (Daniels Stupid Time), named after our former gov who now leads Purdue. Solar noon is at 1:50 PM!
    Two days ago my venerable Yamaha tuner w/timer died after repairs. So I hauled out similar clock radio into which I added a 12 volt relay in place of the worthless radio. Yes the buttons had been fixed before and took a while to wake up themselves. Someone on the web resells 3M stick-on conductive dots. They are used to fix keyboards and organs.
    The point is I wake to a positive accent to begin the day. In this case our NPR station on the whole house system. Alarms are for tornadoes etc. and not to be sounded often or to be an everyday occurrence. They are testing tornado sirens today!
    The point of this hack is crystal transducers. I understand no one makes the venerable crystal mic that blues harp blowers celebrate. This would be a very worthy thing to hack back into real. Also just whats in those lighters, a possible mic hack?

    1. You can get little piezo speakers, little copper or bronze discs with some piezo crystal stuff stuck to one side. Not sure what the difference is between those, and an optimal crystal mic, but a bit of research might tell you. A bit of experimenting might have the blues harp blowers make you their king! I bet their national anthem’s a bit of a racket.

    2. Oh, and the lighters have a little metal hammer against a spring, that’s pushed down by the user pressing the trigger. When it hits the bottom, a catch slides to the side, and the spring drives the hammer into some piezo crystal quite hard, to produce enough voltage, sent down a wire and with another contact on the housing, to produce a spark.

      Dunno what a, say, 2mm spark in air implies, maybe a few hundred volts? Quite a painful shock anyway, once saw a trick pen where the same thing happens when you click the pen. The contacts are just where your fingers go.

      You can take one apart yourself, they’re cheap as dirt. I might guess that something designed to be hit by a hammer for hundreds of volts, is not ideal microphone material, but what do I know? Connect a coil-type voltmeter up and sing at it loud as you can, see what turns up.

      Round here you get 3 lighters for a pound, complete with 3v worth of tiny watch batteries and a blue LED built in one end, for what’s possibly the world’s most useless, blue, torch. I’ve seen white ones too, but if you’re not gonna use white, at least use a colour that’s useful to see with.

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