USB Memory Stick Reminder Cap

Almost was home, back from a client where I fixed some computer problems. Then I realized that I had left my usb memory stick in my client’s computer. Now I had a hard choice, drive back 100 km or let my client send back the usb stick with lots of information he does not need to know. Do you recognize this and do you have fine soldering skills? Then this instructable is something for you. This is an usb cap that sounds an alarm when it has been empty for 5 minutes. The alarm is repeated every minute. When you always keep the cap with you, you will never forget an usb stick again.

Step 1: Parts and Tools

Parts needed:

  • 3 batteries size AG5
  • PIC12F629-I/SN microcontroller (soic 8 package)
  • piezo beeper 20 mm diameter
  • 100nF capacitor (size 1206)
  • 4M7 resistor (size 0804)
  • Some abs plastic
  • Some stripped wire wrap wire (30AWG)
  • Some lacquered wire
  • Small piece of foam


  • 3d printer
  • Soldering iron
  • Tweezers
  • Wire cutter
  • Wire stripper
  • Glue gun
  • pic programmer (pickit 2)
  • 5 pin pin header
  • 1 mm drill

Step 2: Programming the Microcontroller

Connect the microcontroller to the programmer according to the schematic with lacquered wires

program the hex file into the pic chip.

I compiled the source file with the HI-TECH compiler (ver 9.60) in mplab IDE (ver 8.00) If you want to adapt the program and use other versions of the compiler beware that the timing can be different. I found that newer versions of HI-TECH actually are slower. This means that the frequency of the sound is lower.

Step 3: Build the Enclosure.

Print the model from the stl file usb_bleeper.stl You might have to scale the model so that the batteries and usb stick fit. You could also make the casing by other means. My initial prototype was made with instamorph moldable plastic

Step 4: Contacts for Detecting USB-plug

Drill 4 1mm holes in the corner of the rectangular area under the round area. Put some 30AWG wire through the holes. They must contact the metal of the usb plug when it is in.

Step 5: Connecting the Electronics.

Solder the electronics according to the schematic. This very simple schematic can be built without a pcb. Solder the piezo beeper with lacquered wire.

The sens contacts are the 2 wires that go through the holes. The smaller electrode of the batteries is the minus side. On the picture I use smaller type batteries than for what I designed the casing.

Step 6: Close Battery Cap

Put the batteries in together with a piece of foam. The foam must push the wires against the batteries. Glue the battery cap with some hot melt glue. For replacing the batteries the glue can easily be removed by applying some isopropyl alcohol.

Step 7: Glue the Piezo Beeper

Put some tape over the electronics and glue the piezo beeper on top with hot melt glue. For best sound quality the whole rim of the beeper must be covered with glue.

Step 8: Testing

Whenever you put in or take out a usb-plug the device produces a single beep. When you take the plug out and wait 5 minutes you must here 7 beeps. The timing of this chip is not very accurate.



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    8 Discussions


    Better yet, have a “Normally-Closed Momentary switch” somewhere inside the cap, so that when the thumb drive is in the cap it turns the device off completely. This would work with plastic USB plugs, and would save battery life too.

    2 replies

    I tried this. But I find it quite hard to make or find a reliable nc-switch that fits in a small space. any suggestions?


    Well, you do have a 3D printer. All you need are 2 pieces of flat metal leads. Make it so that on of the leads have a small bump in such a way that when the thumb drive is inserted, it is pushing the metal out, and disconnecting it from the other piece of metal lead.

    * I attached an image, I hope you understand it ;-)


    4 years ago

    One thing that could be done is do this as an inline device to the drive instead of a cap. So the USB port would provide the power. This would remove the batteries from the device. Since having batteries go bad would make someone a sad panda. However I think the pic uses 3.3 or 3 instead of 5v

    2 replies

    Reply 4 years ago

    The drive may be somewhere in a server room where nobody will hear it. So you need batteries. I think the pic works from 3 to 5V. In this schematic it is 4.5V. At 3V the sound is not so loud. The short beep when you take of the cap is also for checking the batteries.


    Reply 4 years ago

    Aww yes, did not think of it that way. Forgot how loud server rooms can be.


    4 years ago

    That's a terrific idea. It has a lot of potential as a commercial product.

    1 reply

    Reply 4 years ago

    I know many people who want one. I need someone who wants 10,000 pieces of this product.