Build A Better Mousetrap

They say, “necessity is the mother of all invention”. Well, if that’s true then this project is living proof! Mice beware of the Mouse Motel! This project is designed for mice, but could also be adapted to catch larger animals as well.

The “Better” Mousetrap


If you’re easily grossed-out you may not want to read this part (skip ahead to the build section), but this is what got me started on building this project. My family used to live out in the country in Western NY. It was a nice area and we lived in a small house. Of course, being rural we had mouse problems. Normally we would stick a piece of cheese in a snap-trap and call it good. We had mixed results. Either the mouse would take the cheese and not set off the trap or they’d get nailed and make a mess out of the area where the trap was set! Worse yet, if we didn’t remember to check the trap, our first indication we got something was the smell.

At the time we had a computer shop. When we first moved our shop downtown we were busy for the first two weeks with getting things set up. We were gone all day and so we would come home, eat dinner and go to bed. One day (it was a hot one too) we came home and there was this awful stench coming from in the house…the kind that makes you start gagging as soon as it hits you. Upon entering the house we noticed that there were literally hundreds of flies, something we normally kept under control (I hate flies). My wife suggested that I check the garbage and mouse traps. The last one we checked was one we put in the back of our food cabinet where the mice have a little path between rooms where the water lines come through. As soon as we opened the cabinet we knew we were in trouble. Crawling around our cans and boxes of food were hundreds of maggots! We took a flashlight and looked in the back and there was the remains of a mouse in the trap crawling with maggots. Suffice it to say, by the time we got done cleaning that mess up we vowed to never have to go through that again! Thus, I set out to do what I was good at…design a better solution. And the Better Mousetrap was born.

Building A Better Mousetrap

I thought about how a mousetrap works, its limitations and ultimately, what we wanted. First of all, we didn’t think to check the trap because we were busy and we simply didn’t notice it until it was too late. Also, we needed to keep the mouse alive so that it wouldn’t decompose and draw flies and / or ants.

Some answering machines have a feature that alerts you to new messages by beeping every 10 seconds or so. That way when you come home if you don’t think to check the machine you’re still alerted that there are new messages. I liked this idea. We needed to know when a mouse was caught so we could deal with it as soon as possible. We also needed to catch the critter alive, just in case we were gone away for a while. And of course, we didn’t want a mess! Obviously mangling the mouse was out of the question. My wife doesn’t like the idea of killing anything anyway and she’s right. All creatures have their place…just not in our home.

The Original Prototype

The idea was simple. A small enclosure that the mouse would enter and break an IR beam, similar to how some alarm systems work. When the beam is broken a door closes, trapping the mouse and alerting us to the capture. It sounded so easy. Here’s how it came to be…once I got the idea I threw together this quick prototype so I could see how involved it would end up being. For simplicity (overkill, really) I am using a 2×16 LCD and the sensors aren’t hooked up. Instead I am manually triggering the servo to move. The Better Mousetrap uses a BS2-OEM from Parallax, which may seem a bit overkill, especially with the IR beam break sensor, comparator, LCD, buzzer and servo, but I had the extra parts laying around the bench. Wouldn’t Rube Goldberg be proud?

Once I finalized the hardware design it was time to move everything to a more permanent form. The RadioShack solder-ring board shown is a perfect match for the breadboard I designed the prototype on, so I used it. The power supply is a 6VDC wall adapter I salvaged from an old answering machine. Probably the same one I got the alert idea from. The various components are shown in the second photo. I have labeled the important sections in that photo.

The solder side is shown for those who asked for it. Nothing much to see there, although you can see the standoffs I installed. Also shown is the LCD I used for the final project. Labeled LM575, this 1×15 character display appears to have come from an electric typewriter or word processor. It has icons for typewriter functions, although I did not use them in this project. I acquired this display from a surplus house, probably BG Micro.

On the back side of the LCD I soldered some wires with SIP sockets to the display to make it easy to connect to the SIP header I installed on the control board. These were mainly wire harness assemblies from old computers I had laying around the shop. The left one is a CD-ROM audio cable and the right one is the front panel connectors for an HP computer. These work well for this type of connection. Even better if both ends have the connectors intact. The enclosure, a $5.00 box from RadioShack, has been drilled and the IR LED and Phototransistor have been installed about 2/3 of the way into the box.

Next the servo and LCD mounting brackets have been installed on the cover. The control board and LCD were also installed. After connecting all the wires for the sensors, LCD and servo to the control board we’re ready for downloading the firmware and testing everything out.

Mousetrap Ready

Once the firmware was downloaded the LCD displayed the “AWAITING MOUSE” message. Once the mouse enters the box and breaks the beam, the trap door closes. The completed system is ready to start catching mice! As it turns out we caught three mice in a row over several days. Peanut butter was the preferred bait, although we did try cheese as well.

Other Live-Catch Mousetraps

As a side-note and for those who pointed it out to me, there is a company, Kness Pest Defense that makes a live catch trap that can even catch multiple mice unattended. It is a simple, yet clever device. However, the device doesn’t alert you to having caught any mice and best I can tell, the only way to know is to try and empty the trap or buy an optional see-through door. They also sell an attachment which drowns the mice, which kind of upset my wife. Remember that one of the design goals is to be alerted in case you forget to check the trap. Another person (who shall go unnamed) did email me and suggest that I install electrodes and electrocute the mouse. Let’s keep in mind that, while I have no love for rodents who invade my personal space, this idea deviates from my goal of keeping the mouse alive so it can be relocated. We also don’t want the mouse to die / decompose in case the trap is left unattended for an extended period of time.

Escaped Mouse Flees For Life! Film At Eleven!

Well, it happened. Mouse #4 ate his way out of the box by chewing around the edges of the entrance hole until he bored an opening off to one side of the door, which he squeezed through, pushing the trap door aside. Late at night we don’t usually hear the trap unless we get up during the night. By the time I got to it he was gone!

Chewed Cabinet

Partly my own fault since mouse #2 had started chewing I should have known this was going to be a problem with the plastic case. I had programmed the BS2 to loop toggling the buzzer and LED on/off, but I did not refresh the servo, so it was lax once it closed. I figured there’s no way a mouse could push that door aside, since they couldn’t get a grip on it. But once mouse #4 chewed through enough of the cabinet it was easy to get leverage and push the door aside.

Repair Plate

The solution was to cut out this metal enclosure cover with a slightly smaller hole than the case originally had and bolt it inside the cabinet. Now let’s see these little guys chew their way out of the cabinet! I also fixed the servo issue by updating the code so that the servo is refreshed while the LED and buzzer are pulsating so that it resists a change in position. It will take Mighty Mouse to break out now!

Repaired Box

Here is the repaired cabinet. This was completed Saturday, 06-07-2003. The trap was put back into service that night and Sunday we caught mouse #4 again (we’re sure it’s the same mouse) and this time he didn’t get away! He made an awful racket trying to chew through the metal though. Oh, the sound of teeth on metal is as bad to me as fingernails on a chalkboard is to some others!

Final Thoughts And Ideas

Since my move to CA, I haven’t had a need for a mousetrap until recently. I apologize, I never created a digital schematic for this version, but if I do update / revise it and re-create it I will post the schematic. The last source code I can find for this project is attached in the ZIP file below. Several people have emailed me suggesting that I expand on the idea and make a small network of traps all controlled by a host controller or that I have a remote alarm device. I thought about setting up several traps with an XBee interface so that I could tell which trap caught a mouse by looking at a control panel, either on my phone or PC. Not sure what, if any ideas I will use, but I am planning on making a more permanent version of the trap some day, possibly with a camera that takes a photo of the captured mouse and sends me a text message with it. Perhaps we’ll call it a “critter cam”.


Build A Better Mousetrap V2 – Project

Build A Better Mousetrap V3 – Project

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Build A Better Mousetrap by Chris Savage is licensed under CC BY 4.0


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